REVIEW Open Access

A physiologic approach to cord clamping:Clinical issuesSusan Niermeyer

Abstract

Background: Recent experimental physiology data and a large, population-based observational study havechanged umbilical cord clamping from a strictly time-based construct to a more complex equilibrium involvingcirculatory changes and the onset of respirations in the newly born infant. However, available evidence is not yetsufficient to optimize the management of umbilical cord clamping.

Findings: Current guidelines vary in their recommendations and lack advice for clinicians who face practicaldilemmas in the delivery room. This review examines the evidence around physiological outcomes of delayedcord clamping and cord milking vs. immediate cord clamping. Gaps in the existing evidence are highlighted,including the optimal time to clamp the cord and the interventions that should be performed beforeclamping in infants who fail to establish spontaneous respirations or are severely asphyxiated, as well as thosewho breathe spontaneously.

Conclusion: Behavioral and technological changes informed by further research are needed to promoteadoption and safe practice of physiologic cord clamping.

Keywords: Umbilical cord, Placental transfusion, Resuscitation, Respiration, Infant, Newborn, Infant, Premature

Background

“In the time of Hippocrates the cord was not cut untilthe placenta was delivered….Since the time of Levret ithas been established as a general rule, amongaccoucheurs, to separate the child from the mother assoon as it has passed through the vulva, and that it isnever necessary to wait for the expulsion of the foetalappendages. At first view the conduct of the ancientsappears to be more rational and more physiologicalthan that of the moderns; it seems that the placentaought immediately to follow the foetus, or at least beseparated from the uterus before the cord can beprudently cut; that before it is divided, the circulationought to be permitted gradually to take on its newtype, which soon becomes similar to that of the adult;but in reality it is not perceived that the present modeof practice produces the least inconvenience to thefoetus, and is certainly better for the mother.” 1

– Prof. A.A. Velpeau, 1829 [1]

For centuries, lively debate has surrounded thequestion of when to clamp and cut the umbilical cord ofthe newly born infant, and practices have ranged fromone extreme to the other. From the time of the AncientGreeks, midwives have described the value of waiting toclamp the cord until pulsations stop or until the pla-centa is delivered [1]. This approach is taken to its fur-thest modern extent in Lotus birth, when the umbilicalcord and placenta remain attached to the infant untilnatural separation at the umbilicus occurs after severaldays. As Prof. Velpeau pointed out in his Treatise onMidwifery in 1829, a different practice arose amongaccoucheurs, male midwives or obstetricians, whoperceived that immediate cord clamping and cuttingoffered benefit to the mother and posed no “incon-venience” to the newborn [1]. Recently, the obstetricalpractice of immediate cord clamping has been modi-fied by policy statements from the American Collegeof Obstetricians and Gynecologists (ACOG), the RoyalCollege of Obstetricians and Gynaecologists, and theThe Royal College of Midwives [2–4]. The ACOGstatement received endorsement from the AmericanAcademy of Pediatrics [5]; the International Liaison

Correspondence: susan.niermeyer@ucdenver.eduSection of Neonatology, University of Colorado School of Medicine, 13121 E.17th Avenue, Mail Stop 8402, Aurora, CO 80045, USA

© 2015 Niermeyer. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Niermeyer Maternal Health, Neonatology, and Perinatology (2015) 1:21 DOI 10.1186/s40748-015-0022-5

Committee on Resuscitation recommended delayedcord clamping for infants who do not require imme-diate resuscitation [6]; and the World HealthOrganization (WHO) reiterated their recommendationto delay cord clamping for 1–3 min while initiatingsimultaneous essential newborn care [7]. Still, allcurrent practice guidelines vary slightly in their em-phasis and details, and all suggest that delayed cordclamping may not be feasible or desirable in everysituation, especially when immediate resuscitation isrequired. This review will relate recent experimentalphysiology data to clinical studies, examine thepractical dilemmas faced by clinicians, and identifygaps in knowledge as well as directions for further re-search to more fully define a physiologic approach tocord clamping.

FindingsPhysiology of umbilical cord clampingPhysiologic data from experimental animals have changedthe frame of reference for umbilical cord clamping from astrictly time-based construct to a more complex equilib-rium between the circulatory changes accompanying theonset of respirations and completion of the circulatoryand respiratory functions of the placenta. In an accom-panying article, Hooper et al. describe in detail the differ-ences in heart rate, right ventricular output, carotid arterypressure and flow, and pulmonary and ductus arteriosusblood flow encountered with immediate cord clampingbefore onset of respirations vs. delay in cord clampinguntil after ventilation in anesthetized preterm lambs [8, 9].

Table 1 Targets for further research on physiologic umbilicalcord clamping

Population

Extremely low birth weight/extremely preterm infants

Infants with evidence of asphyxia – antepartum/intrapartum

Infants born in low-resource settings

Intervention (delayed cord clamping with multiple covariates)

Antenatal corticosteroid administration before preterm birth

Type of maternal anesthesia

Uterine activity (contractions or operative delivery without labor)

Administration of uterotonic relative to cord clamping

Onset of respirations relative to cord clamping

Spontaneous

Assisted ventilation

Position of infant relative to placenta

Duration of delay before clamping

Comparison

Delay in cord clamping with and without resuscitation

Initial steps (drying, clearing airway, specific stimulation to breathe)

Positive-pressure ventilation

Sustained inflation

CPAP

Intermittent positive-pressure ventilation

Umbilical cord milking vs. delayed cord clamping

Active milking (length of cord segment, rate, number of passes)

Draining of cord segment

Outcome

Need for resuscitation

Physiologic characteristics during postnatal stabilization

Temperature

Blood pressure

Blood glucose

Need for volume expanders/pressors (per defined criteria)

Regional blood flow – e.g. cerebral

Hemoglobin/hematocrit/iron status

Blood volume

Need for transfusion (per defined criteria)

Complications of prematurity

Intracranial hemorrhage/periventricular leukomalacia

Necrotizing enterocolitis

Bronchopulmonary dysplasia/duration of supplemental oxygen

Patent ductus arteriosus

Hyperbilirubinemia

Premature and term infants

Populations at high risk (genetic variations)

Settings with limited access to phototherapy

Table 1 Targets for further research on physiologic umbilicalcord clamping (Continued)

Polycythemia

Term infants and growth-restricted infants

Technique-specific differences (delayed clamping vs. umbilicalcord milking)

Neurodevelopment

Toddler, preschool, elementary school outcomes

Sex-specific differences

Correlation with iron status

Brain microstructure/development (advanced imaging i.e. MRI)

Behavior

Prevalence/duration of exclusive breastfeeding

Mortality

Maternal obstetrical outcomes

Physiologic characteristics postpartum

Postpartum hemorrhage

Intraoperative complications

Niermeyer Maternal Health, Neonatology, and Perinatology (2015) 1:21 Page 2 of 13

At birth, the function of respiration shifts from theplacenta to the infant’s lungs, as they expand first withair and then with a large increase in pulmonary bloodflow. During fetal life, placental blood passes throughthe umbilical vein and ductus venosus to the rightatrium, where it primarily streams across the foramenovale to provide preload for the left ventricle (Fig. 1).Systemic fetal venous return also enters the right atriumand passes into the right ventricle; however, only a smallpercentage of total right ventricular output passesthrough the lungs. Most right ventricular output divertsvia the ductus arteriosus to the descending aorta whereit perfuses fetal organs or returns to the placenta via theumbilical arteries. When breathing begins, much moreof the right ventricular output flows to the lungs and

placental blood maintains ventricular preload. As thepulmonary circuit fills, pulmonary blood return to theleft atrium gradually increases to serve as preload for thesystemic circulation. In the process, pulmonary vascularresistance falls, right heart pressure falls, and theforamen ovale functionally closes [10, 11]. When theumbilical cord remains intact as a healthy infant beginsbreathing, the shift in respiratory function from placentato lungs is accompanied by a physical shift in bloodvolume from the placenta to the newly born infant tomaintain circulatory equilibrium as the pulmonary vascularbed opens.If the umbilical cord is clamped before breathing begins,

systemic blood pressure rises with loss of the low-resistanceplacental circuit and still-high pulmonary vascular

Fig. 1 Schematic of the fetalcirculation (http://www.heart.org/HEARTORG/Conditions/CongenitalHeartDefects/SymptomsDiagnosisofCongenitalHeartDefects/Fetal-Circulation_UCM_315674_Article.jsp)

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resistance preventing left-to-right flow through the ductusarteriosus. There follows a loss of preload to the leftventricle which results in a steep fall in cardiac output [12].If there is delay in establishing respirations, hypoxemia alsoensues, potentially resulting in postnatal hypoxic-ischemicconditions. Compensatory mechanisms move circulatingvolume from the peripheral to central circulation. Onlywhen pulmonary vascular resistance falls does pulmonaryblood flow increase through right ventricular outflow andleft-to-right shunting through the ductus arteriosus.Pulmonary venous return to the left atrium then restoresleft ventricular preload, cardiac output, and systemicpressure [9, 13].Reaching the point of circulatory equilibrium in the

transition from placental to pulmonary respiration re-quires a variable amount of time, depending on the indi-vidual circumstances at birth. Various lines of data fromearly physiological studies suggest that the transitionusually lasts several minutes [14]. In ventilated lambs,pulmonary blood flow reaches a maximum only after5–10 min [15]. Measurement of residual placentalblood volume in human infants describes rapid trans-fer of blood initially, followed by slower rate of trans-fer documented through 3 min or more [16] (Fig. 2).Measurements of actual umbilical vein flow by dye di-lution follow a similar pattern in healthy term infants,with high flow in the first 2 min, followed by a vari-able decrease [17]. More recent studies show a similarpattern of increase in infant weight after birth whenthe umbilical circulation remains intact [18]. UmbilicalDoppler blood flow patterns immediately after birth arehighly variable, but flow may continue up to 10 min [19].Electrical impedance measurements show an increase incardiac output through 3–5 min in the majority of infants[20]. Experimental and clinical physiological data are gen-erally consistent in suggesting that reaching circulatoryequilibrium requires several minutes, even under idealcircumstances.A single large, population-based observational study of

infants in a resource-limited setting in Tanzania reportedan association between the timing of umbilical cordclamping relative to the onset of spontaneous respirationsand the outcomes of death or admission to a special carearea [21]. The cohort of 12,730 term and preterm infantswas selected on the criterion that all established spontan-eous respirations and received only routine care. Theywere judged to be healthy and strong by the deliveringmidwives. Independent observers documented the timingof key interventions and infant responses at all deliveries.Variation in the time of umbilical cord clamping occurredas the facility transitioned from the previous practice ofimmediate cord clamping to a new routine of cord clamp-ing delayed for 1–3 min. Special care in the neonatal areawas limited to administration of antibiotics and

intravenous fluids. Logistic modelling showed the risk ofdeath/admission to the special care area by 24 h was con-sistently higher if cord clamping occurred before spontan-eous respirations. Risk of death or admission decreased by20 % for every 10-s delay in cord clamping after spontan-eous respiration up to 2 min. Death/admission occurredmore frequently in infants of low birth weight (<2500 g)and preterm gestational age; however the described rela-tionship held in both normal weight and low birth weightinfants. In a setting where cardiorespiratory or even

Fig. 2 Various lines of evidence (a residual placental blood volume,b umbilical blood flow by dye dilution, c infant weight) demonstratingcontinuation of umbilical blood flow for several minutes after birth(permission requested) [57, 18, 17]

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general supportive care was not available to buffer physio-logic derangements, the impact of cord clamping beforeonset of respirations manifested as increased risk of deathand instability, and delay in cord clamping through 2 minhad a dose-dependent effect of decreasing that risk.Although the physiological data and clinical data from

resource-limited settings indicate a clear and importantrelationship between onset of respirations and the timingof cord clamping, the situations faced by clinicians arecomplex and variable. Available literature does not yetprovide sufficient high-quality evidence to address man-agement with complications such as intrapartum asphyxia,fetal growth restriction, or extreme prematurity. Whilesome data on physiologic outcomes exist, primary out-comes have more commonly related to hemoglobin/hematocrit and volume of placental transfusion. Thus,there are gaps in the existing evidence to guide manage-ment, and clinicians face a number of dilemmas,including:

� Timing – What is the optimal time to clamp thecord in term and preterm infants who breathespontaneously, fail to establish spontaneousrespirations, or are severely asphyxiated? Shouldresuscitative interventions be performed during theinterval before clamping to stimulate breathing orbegin assisted ventilation?

� Technique – does umbilical cord milking offerequivalent or superior outcomes to delayed cordclamping? What is the interplay of umbilical cordmilking and onset of respirations?

� To be determined – what gaps in knowledge, skills,and technological support impede the adoption andsafe practice of physiologic cord clamping in theclinical setting?

Timing: optimizing the relationship between cord clampingand onset of respirations

“If a careful attention be paid to what happens afteran ordinary birth, it will be seen that the pulsationsgrow weaker and soon disappear in the cord,beginning at the placenta, and that after a fewminutes it may be cut without being followed by theleast hemorrhage. This remarkable phenomenon whichis attributed to the change of direction of the iliacarteries, and to the difficulty experienced by the bloodin passing into the aorta through the ductusarteriosus, and into the cord through the umbilicalarteries, always takes place where everything occurs ina natural and regular order, but in reality dependsupon the circumstance that the attractive force exertedby the placenta upon the blood, is replaced by that ofthe respiratory organ, and that the after-birth is no

longer anything more than an inert substance, withoutvitality, which is abandoned by the blood, as it aban-dons a gangrenous or asphyxiated limb.” 2

The clinician is faced with a number of uncertaintiesbefore the delivery of a newborn. Will the lungs bemature? Will the baby cry and breathe spontaneously?Will an acute intrapartum hypoxic-ischemic event or anobstetrical circumstance preclude delayed cord clamp-ing? The answers to each of these may become apparentonly at the moment of delivery, yet they all potentiallyinfluence management of umbilical cord clamping andimmediate care of the newly born infant. The availableevidence relating to physiologic outcomes for term andpreterm infants who breathe spontaneously can helpguide clinical practice. The limited data from babies whoare born in either primary or secondary apnea help toframe gaps in knowledge and suggest practical ap-proaches to management and further research.

Spontaneous cry in term infantsThe healthy term infant who cries spontaneously andbreathes well often accomplishes the crucial first mo-ments of circulatory transition with an intact umbilicalcord, even when clamping is not deliberately delayed.Early physiological studies of residual placental bloodvolume demonstrated that a relatively larger proportionof the fetoplacental blood volume resides in the fetus atterm as compared to earlier in gestation. Spontaneouscry before umbilical cord clamping significantly increasesthe volume of placental transfusion and hematocrit [22].The curve of blood volume transferred vs. time as con-structed by Yao highlights that more than half of the totalblood transfer occurs within the first minute [16]. Amonghealthy term infants delivered vaginally, position at theperineum or on the mother’s abdomen/chest does not sig-nificantly affect the volume of placental transfusion whenclamping is delayed until 2 min [23]. Umbilical vein flow,as measured by dye dilution, is fastest in the first 1–2 minand slows variably thereafter [17]. Doppler ultrasound ofumbilical blood flow patterns immediately after birth re-veals highly variable flow duration and direction in boththe umbilical artery and vein. Flow continues longer thanpreviously described, with flow documented in some casesat the time of cord clamping between 5 and 10 min. Inaddition, the presence of cord pulsations does not neces-sarily signify ongoing flow, and cessation of pulsations canoccur with or without flow [19].Most literature examining clinical outcomes of delayed

cord clamping in term infants reports primary outcomesrelated to volume of placental transfusion and/orhematocrit and relatively few secondary physiological end-points. Meta-analysis of trials in term infants confirms thatnot only are acute measures of blood volume and

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hematocrit generally improved among infants with delayedclamping, but indices of iron status in infancy are also im-proved [24]. This has important implications in the preven-tion of iron-deficiency anemia and the associated sequelaeof impaired cognitive, motor and behavioral development.While the global burden of iron deficiency anemia is great-est in sub-Saharan Africa and Southeast Asia, improvementin hematologic indices occurs even in highly developed in-dustrialized countries such as Sweden [25]. Although short-term neurodevelopmental outcome showed no difference,follow-up at 4 years of a cohort of term Swedish infantswith clamping delayed until 3 min shows improved pro-cessing speed, fine motor and personal-social scores com-pared to infants with immediate clamping [26, 27].Another behavioural outcome of potential significance isthe observation of improved rates of exclusive or predom-inant breastfeeding after hospital discharge [28]. One pos-tulated linking mechanism is improved physiologicstability and alertness in the hour immediately after birth,promoting successful early initiation of breastfeeding,which in turn increases the duration of breastfeeding andthe likelihood of exclusive breastfeeding through 4 monthsof life [29]. Studies of skin temperature in the days afterbirth support improved physiologic stability in late-clamped term infants and give indirect evidence for per-ipheral cutaneous vasoconstriction among those with earlyclamping. Infants with cord clamping delayed until pulsa-tions stopped (average 3 min and 38 s) show significantlyhigher heel and palm temperatures than the group withimmediate clamping, but no difference in epigastric orrectal temperatures [30]. Physiologic studies of cardiacand haematological indices show transient alterations con-sistent with increased circulating red cell volume but nosystematic evidence of increased need for special care (i.e.for hyperviscosity/polycythemia or respiratory distress)[31–34].In practice there is evidence to support a delay of two

minutes or more, while providing routine care, beforeclamping the umbilical cord of the healthy term new-born. There is presently no accepted clinical sign

indicating that circulatory equilibrium has been achievedbetween the newly born infant and the placenta. Themidwifery literature describes “flattening” of the cord(Fig. 3) as a correlate for completion of the placentaltransfusion [35] and cessation of pulsation also has beenused as an endpoint. Position at the introitus or on themother’s abdomen appears equivalent for the vigorousterm infant [23]. Routine care at vaginal delivery, includ-ing thorough drying, any necessary clearing of the airway,thermal protection (skin-to-skin contact with mother),and monitoring of breathing, can occur during the delaybefore clamping and cutting the cord. At caesarean sec-tion, the infant can be placed between the mother’s legson the sterile field and routine care can be provided withwarmed, sterile towels for drying. Although skin-to-skincontact cannot occur during the delay at caesareansection, the infant can be positioned skin-to-skin with themother above the anesthesia barrier drape immediatelyafter dividing the cord. This requires that the mother bealert under regional anesthesia and supported by thecontinuous presence of a nurse to monitor the infant’scondition and safe positioning [36].

Variable establishment of respirations in preterm infants

“I once received a human foetus, at the sixth month ofpregnancy, enclosed within its membranes. Theumbilical arteries continued to beat strongly as long asthe membranes were unruptured; but they fell intoinertia as soon as the lungs and chest, upon coming incontact with the air, attempted to perform somerespiratory movements. And do we not every day see theblood flow or stop spontaneously in the same child,accordingly as the respiration is free or embarrassed?” 3

The preterm infant who is healthy may cry and breathespontaneously or may have delayed onset of spontaneousrespirations or shallow, irregular breathing after birth [37].When general anesthesia at preterm delivery is necessaryfor maternal medical or obstetrical conditions, the newly

Fig. 3 Change in appearance of the umbilical cord from birth, to 12 and 23 min after birth, with umbilical cord intact and completion of thirdstage of labor at 30 min (appleblossomfamilies.com, Morag Hastings, photographer)

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born infant may be completely apneic, although notasphyxiated, and require positive-pressure ventilation forlung expansion. Preterm infants manifest increasedvulnerability to end-organ injury in the cerebral and intes-tinal circulations (intracranial haemorrhage and necrotizingenterocolitis), making ventilation of the lung prior to um-bilical cord clamping and smooth cardiovascular transitiontheoretically even more desirable. Yet, very few humanstudies have explored the physiologic changes around res-piration and cord clamping in preterm births.Much of the literature reporting clinical outcomes

of delayed cord clamping in preterm infants reportsprimary outcomes related to volume of placentaltransfusion and hemoglobin/hematocrit with some add-itional secondary physiological endpoints. Multiple small,randomized controlled trials and several meta-analysesconfirm higher hematocrit at birth and decreased need fortransfusion during hospitalization [38]. There is also evi-dence for improved cardiovascular stability, with highermean blood pressure at 1 and 4 h after birth [39–42],higher measured blood volume [43, 44] and higher super-ior vena cava flow [45, 46]. Two major preterm morbid-ities, intracranial hemorrhage (all grades) and necrotizingenterocolitis, occur less frequently among infants who re-ceived delayed cord clamping. However, severe intracra-nial haemorrhage (grades III and IV) and mortality todischarge do not differ between groups. Temperature onadmission to a newborn area does not differ; the rate ofhyperbilirubinemia treated with phototherapy and thepeak serum bilirubin are higher after delayed cord clamp-ing, but criteria for treatment vary widely [38]. Two ran-domized trials have reported neurodevelopmentaloutcome (Bayley II scores), at 7 or 18–24 monthsage, showing no difference in Mental DevelopmentalIndex < 70, but very wide confidence intervals [47].Two large observational studies with comparison

groups report intermediate physiologic outcomes aspart of quality improvement programs introducing de-layed cord clamping for preterm infants [48, 49].Very-low-birth-weight (VLBW) infants with delayedcord clamping received less delivery room resuscita-tion (supplemental oxygen, bag and mask ventilation,intubation, compressions, medications) compared tothe immediate cord clamping group (61 vs. 79 %, p = 0.01),but there was no difference between groups among low-birth-weight (LBW) infants (30 vs. 27 %). The second studyreported no difference in the need for ventilation in the de-livery room among infant 24–34 weeks gestation [49].Blood pressure in the first 2 days of life was higher in LBWlate-clamped infants, but not different between the VLBWgroups [48]. Mean temperature was in the normalrange but higher for infants compliant with delayedcord clamping, and the incidence of temperature <36.3C was decreased in this group [49]. In both

studies, health care providers could clamp the cord ifthey felt it necessary; 6 of 249 infants [48] had de-layed clamping abandoned to begin immediate resus-citation, and 12 of 236 infants [49] remained apneicand inactive after 20 s of assessment, prompting de-layed clamping to be abandoned.For the clinician, there is insufficient strong evidence

to guide either the length of the delay before clampingthe umbilical cord or the extent of resuscitativeinterventions provided to preterm infants during a delay.In many trials, no resuscitative intervention was pro-vided; in other studies, infants were provided the initialsteps of resuscitation (drying, positioning and clearingthe airway as needed, specific stimulation to breathe i.e.rubbing the back) [43, 48]. Theoretical and practicalchallenges merit carefully controlled trials of beginningpositive-pressure ventilation with intact umbilical circu-lation. Although positive-pressure ventilation may be ne-cessary to aerate the lung and increase pulmonary bloodflow, experimental animal studies suggest excessive end-expiratory pressure or mean airway pressure may notonly cause lung injury, but may also impair cardiovascu-lar transition and result in potential cerebral injury [50].

Fig. 4 Platform for resuscitation at the beside with umbilical cordintact (LifeStart, Inditherm plc, Rotherham, United Kingdom)

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The physical arrangement necessary to provide positive-pressure ventilation calls for collaboration between pro-viders caring for the mother and those caring for thenewly born infant. A small trial has demonstrated thefeasibility and acceptability of a compact, adjustable re-suscitation platform (Fig. 4) which can be positionedclose to the perineum at normal and assisted vaginalbirth or the abdominal incision at caesarean section[51]. Alternatively, a flat, dry, firm surface can be posi-tioned at the perineum on the unbroken delivery bed or onthe mother’s legs at caesarean section. Use of a t-piecedevice for ventilation or CPAP limits the equipment intro-duced into the field of the delivery or the sterile field atcaesarean section. Delayed cord clamping may requiremodification of routines for thermal protection with poly-ethylene wrap or bags. However, contemporary observa-tional cohorts suggest that improved placental transfusionmay help maintain body temperature [48, 49]. Randomizedcontrolled trials using a package of interventions addressingcord clamping, initial support of breathing/positive-pres-sure ventilation, low supplemental oxygen, and thermalprotection will be challenging, but vital to ascertain the realpotential of these interventions combined.

Asphyxia and secondary apnea in term or preterm infants

“Where there is reason to believe that the placenta stillmaintains a part of its natural relations with thewomb, and especially where there is still some tremour,some pulsation in the cord, we may follow the advice…not to cut it too soon; but if the womb be wellcontracted, if the adhesions of the placenta beevidently destroyed, it would be better to separate thefcetus at once from its mother.” 4

The asphyxiated term or preterm infant presentsunique physiological circumstances around umbilicalcord clamping. Early literature suggests that antepartumasphyxia is accompanied by in utero transfer of bloodvolume from the placenta to the fetal circulation [52–54].Data from dye-dilution studies of the umbilical circulationin term asphyxiated infants support lower flow ratesimmediately after birth compared to healthy controls [55].In contrast, acute intrapartum asphyxial events, such astight nuchal cord or shoulder dystocia, may be accompan-ied by cord occlusion and hypovolemia. In either setting,with severe hypoxia-ischemia, the myocardium and thecerebral circulation may be particularly vulnerable to fur-ther insult from immediate clamping of the cord. Theresultant loss of preload and transient decrease in cardiacoutput are likely to produce bradycardia, swings in cere-bral perfusion, and further interruption in blood flow tothe renal, gastrointestinal, and pulmonary circulation. Al-though the volume of blood transferred after birth may be

reduced or increased compared to non-asphyxiatedinfants, the maintenance of a patent umbilical circulationat least until ventilation has been established may limitfurther injury. However, chest compressions in the settingof intact umbilical circulation theoretically could fail togenerate the diastolic pressure vital for coronary perfusionand return of spontaneous circulation because of the large,low-resistance vascular bed in the placenta [56]. There isalso theoretical concern that hydrostatic pressure resultingfrom the relative position of infant and placenta may exerta substantial effect on the direction/volume of bloodtransfer in the setting of asphyxia [57].Management of umbilical cord clamping in the as-

phyxiated term or preterm infant has received littleattention in recent randomized controlled trials; usu-ally the need for immediate resuscitation has consti-tuted a criterion for exclusion. The logistic challengesof conducting an extensive resuscitation, includingpossible need for immediate intubation, chest com-pressions, and umbilical line placement for medica-tion administration, argue for use of a specializedresuscitation platform for initial management proxim-ate to the field of delivery. Once the initial steps ofresuscitation and lung expansion have been accom-plished, the infant can be relocated for more exten-sive interventions.

Technique: cord milking as an alternative to delayed cordclamping

“In the time of Aristotle the midwives were in the habitof forcing the blood contained in the cord into the bellyof the fcetus before they tied it, and pretended bymeans of this practice, which has been revived at thecommencement of the present century, to restorestrength and vigour to feeble children.” 5

Cord milking offers an alternative to delayed cordclamping for facilitation of placental transfusion. Cordmilking typically involves compressing the blood from a20–30 cm segment of cord into the infant over 2–3 s;usually this procedure is repeated three times, allowingthe umbilical vessels to refill from the placental side be-tween milking [58]. To maximize transfer of blood, coilsin the umbilical cord must be untwisted first. Whenthere is great urgency, the cord can be immediatelyclamped close to the placental side, suspended over theinfant on the resuscitation platform, and milked orpassively drained as resuscitative interventions begin.Measurement of residual blood volume in the umbilicalcords of extremely preterm infants estimates the volumecontained in a 30-cm segment of cord at approximately17 mL/kg [59]. The residual volume tended to be

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reduced in the cords of infants with low weight forgestational age.The evidence base for umbilical cord milking is

more limited than that for delayed umbilical cordclamping. Meta-analysis of five small randomized con-trolled trials in preterm infants < 33 weeks showshigher initial levels of hemoglobin and hematocrit, aswell as lower incidence of intracranial haemorrhage ofall grades in infants who received umbilical cordmilking as compared to immediate clamping [60].One recent trial reports that preterm infants in theumbilical cord milking group had higher heart rateover the first 2 min, higher oxygen saturation in thefirst minutes with less supplemental oxygen, and re-duced need for supplemental oxygen at 36 weeks[61]. Preterm infants < 32 weeks born by caesareandelivery show higher superior vena cava flow in thefirst 12 h with umbilical cord milking as compared to45–60 s of delay in cord clamping [62]. The meta-analysis finds no difference in mortality before dis-charge, hypotension requiring volume or inotropes,need for transfusion, severe intraventricular haemor-rhage, peak serum bilirubin or need for phototherapy[60]. Only one study followed infant to 24 months fordevelopmental outcome, finding no difference in ratesof disability [47]. Two small randomized controlledtrials in infants > 35 weeks report higher hemoglobinimmediately after birth. Of 224 total infants, nonehad symptomatic polycythemia. There was no differ-ence in the peak serum bilirubin or the need forphototherapy [63, 64].In practice, umbilical cord milking offers the primary

advantage of speed. The actions can be completed in amatter of seconds, the maneuvers are readily accom-plished at caesarean section, and the baby can be imme-diately transferred to the pediatric team for any neededresuscitation. Entire surgical teams do not need to pauseduring a caesarean section, and the obstetrical providerat a vaginal delivery can immediately move to controlledcord traction. The action of milking the cord requiressome standardization of practice, however, as the helicalspirals of the cord create obstruction to blood flow ifnot untwisted prior to milking. The length of the seg-ment milked, speed, and number of repetitions of milk-ing have been established by pragmatic choice ratherthan controlled experiments. Transfer of blood occursas a bolus rather than a process of equilibration as withdelayed cord clamping; milking often is accomplished in15 s or less [61]. If respirations have not been estab-lished prior to clamping the cord, the volume ofblood retained in the infant’s circulation may not beas large as if the pulmonary circulation has expanded.Hemodynamic fluctuations similar to those described withimmediate cord clamping theoretically could occur; the

hemodynamic significance of retrograde flow in the um-bilical arteries also is unclear. Additional concerns arisearound potential volume overload in infants who have ex-perienced hypoxic-ischemic events during labor and in-creased products of endothelial activation entering theinfant’s circulation with milking of the umbilical arteries[65].

To be determined: gaps in knowledge and practice

“Instead of coming into the world pale, anemic, orexsanguinous, the child is sometimes born in quite acontrary condition; its skin is of a bluish red or livercolour, of various degrees of intensity, especially on theface, and appears as if thickened…..The apoplecticstate is met with, especially in strong children, afterlong and difficult labours, the application of theforceps, and pelvis labours, either spontaneous orartificial; where the child has remained for severalhours under the influence of the uterine contractionsafter the discharge of the waters; where it haspresented in a bad position; where it is too large topass with ease through the various passages; where aloop of the cord strictures its neck, or is itself in anyway compressed, and particularly where any of theseaccidents occur coincidently with a previous plethoricstate. When a child is born in this state we shouldmake haste to disengorge its vascular system…” 6

When is physiological cord clamping not feasible orbeneficial?Widely varying conditions have been considered as ex-clusions from delayed cord clamping or umbilical cordmilking in published trials. Hemorrhagic complicationsduring labor (i.e. placental abruption and placenta pre-via) and cord abnormalities or accidents (true knot, pro-lapse, avulsion) may physically interrupt placentaltransfer. Tight nuchal cord which cannot be reducedconventionally may be reduced by using the somersaultmaneuver, permitting delayed clamping or cord milking[66]. In multiple gestations with evidence of placentalconnections (monochorionic placentation, twin-twin-transfusion syndrome) or discordant growth, facilitatingplacental transfusion poses theoretical risk to the secondtwin and potential to exaggerate polycythemia/hypervo-lemia. Hemolytic disease has been viewed as a contra-indication because delayed clamping increases thevolume of sensitized red blood cells; however the relativerisks/benefits of hypovolemia and hemodynamic labilityat birth vs. larger bilirubin load have not been carefullystudied.Questions arise around a number of maternal and fetal

conditions which might represent relative contraindications

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to facilitated placental transfusion. Growth restriction, espe-cially if a result of chronic intrauterine hypoxia, may be as-sociated with higher risk for polycythemia andhyperviscosity. Maternal diabetes and pre-eclampsia alsorepresent circumstances associated with intrauterine hyp-oxia. Non-vigorous infants born through meconium-stained amniotic fluid have historically undergone immedi-ate intubation for tracheal suctioning, prompting immedi-ate cord clamping. Programs focusing on prevention ofmaternal-to-child transmission of HIV previously ad-vocated immediate clamping as part of the package ofinterventions; in the absence of any evidence or lo-gical mechanism of increased viral transmission,WHO recommendations now explicitly advocate de-layed cord clamping in this situation [7].

What factors determine the volume/rate of blood transfer andwhat clinical indicators can aid in establishing the point ofhemodynamic equilibrium?During either delayed cord clamping or umbilicalcord milking in the clinical setting there is littlecertainty about the volume, rate, or direction of bloodtransfer. The onset of spontaneous respirations andopening of the pulmonary vascular bed are now rec-ognized as major determinants of placental bloodtransfer. However, other factors have been demon-strated to influence the equilibrium of placental trans-fusion, including uterine contractions (or their absence atcaesarean section), administration of uterotonics, physicalposition of the newly born infant relative to the placenta,gestational age, and antepartum/intrapartum hypoxic-ischemic conditions [67]. A variety of experimental tech-niques have been used in human infants to documentblood flow and net transfer. Highly accurate scales havebeen used to document the time course and estimate thevolume of placental transfusion with delayed cord clamp-ing [18]. In the 1960s impedance plethysmography wasused to study the relative contributions of lung aerationand pulmonary blood flow during delayed cord clamping[68]. Modern electrical impedance tomography (EIT) con-verts impedance signals into images and may offer theprospect of studying lung recruitment and the dynamicsof delayed cord clamping simultaneously and noninva-sively. Doppler flow measurement has proven feasible forthe measurement of umbilical cord flow, as well as cardiacoutput, regional blood flow, and tissue perfusion. Near-infrared spectroscopy offers insight into cerebralhemodynamics with non-invasive, bedside methods [11,69]. Experimental animal studies offer the possibility ofmultiple simultaneous and direct measures of blood flow,pressure, volume as well as advanced imaging using suchtechniques as scintigraphy and magnetic resonance imaging(MRI). More attention could also focus on description ofclinical correlates of adequate placental transfusion, such as

capillary refill in the infant or appearance of the umbilicalcord. In parallel with lung recruitment, the timing of cordclamping as a patient-defined strategy deserves further re-search to define useful measures and clinical signs ofphysiological equilibrium [70].

What changes in infrastructure and human behaviour arenecessary?While uncertainties still exist around the best approachto achieve physiologic cord clamping, incrementalchanges in practice are now possible [71, 49, 48]. Themodel of gradual transition in circulation and respiratoryfunction from the placenta to the lungs should serve asthe model for collaboration between obstetrical andpediatric providers at a birth. Both disciplines need tocommunicate and formulate a plan before birth toaccomplish a smooth transition; both need to be in-volved in monitoring third stage of labor in the motherand signs of circulatory transition and equilibrium in thenewly born infant; both need to promptly detect and re-spond to deviations from the normal postnatal course.Waiting is difficult, especially waiting without action fora process that is largely invisible and incompletelyunderstood. Active monitoring of umbilical cord appear-ance/pulsatility as well as uterine contractions/placentaldetachment and active provision of routine care or theinitial steps of resuscitation turn passive waiting into ac-tion and provide shared learning and experience withclinical signs of physiologic transition and equilibrium.Although umbilical cord milking also eliminates passivewaiting, controlled comparisons of delayed cord clamp-ing vs. umbilical cord milking are necessary before it canbe established that cord milking and rapid clamping/cutting pose “not….the least inconvenience” for thenewly born infant.Delay in term infants has often been limited to one

minute, which may be insufficient to complete theprocess of placental transfer to a point of equilibrium.Observational studies in term infants to determineoptimal timing should examine carrying out the steps ofroutine care with the newly born infant on mother’s ab-domen to safely prolong the delay and set the stage forearly initiation of breastfeeding. However, in many set-tings, maintenance of skin-to-skin contact in the firsthour and facilitation of breastfeeding demand consider-able change in provider workflow to provide adequatesupport and monitoring of mother and baby.Delay in umbilical cord clamping of premature infants

in many studies has been in the range of 30–45 s only;these studies very likely have not captured the full po-tential benefit of delayed cord clamping to preterm in-fants. Assuring thermal protection and providing theinitial steps of resuscitation to preterm infants duringdelay in cord clamping can safely prolong the delay and

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possibly achieve onset of respirations in the majority ofinfants. Performing the initial steps of routine care or re-suscitation during delay deserves comparison with um-bilical cord milking.Delivery of positive-pressure ventilation to achieve

lung expansion before umbilical cord clamping calls forre-design of communication and the physical interactionbetween obstetric and pediatric providers, as well as theequipment for resuscitation. Although equipment forsuctioning and ventilation can be readily adapted tospace and sterility constraints, monitoring currentlyproves more cumbersome. Disposable colorimetric car-bon dioxide detectors may offer a useful summative in-dicator for both ventilation and pulmonary blood flow;delivery of carbon dioxide to the alveoli requires pul-monary blood flow and delivery of carbon dioxide to thedetector requires unobstructed pulmonary ventilation.Color change has been shown to be useful in detectingairway obstruction during bag and mask ventilation andpredictive of restoration of normal heart rate in the set-ting of bradycardia immediately after delivery [72].There is considerable potential for further developmentof monitoring, such as transthoracic impedance andquantitative end-tidal carbon dioxide, that would givereal-time information on progress of the physiologictransition after birth.In resource-limited settings, the balancing outcomes

of temperature stability and hyperbilirubinemia deserveclose consideration. Thermal protection during delay inumbilical cord clamping may require different strategieswhere control of environmental temperature and use ofchemical warming mattresses are limited. It is unclear ifdelayed cord clamping in preterm infants would increasedemand for phototherapy beyond available capacity inareas where specialty care is limited.

Directions for further researchWhat are the broader implications of physiologic umbilicalcord clamping for neonatal clinical research?Research is now needed to investigate how the beneficialeffects of physiologic transition can be maximized (Table1). With respect to umbilical cord clamping, this meansre-orientation of research to clearly document the tim-ing of cord clamping in relation to the onset of respira-tions in all studies and to place new emphasis oncollection of immediate and intermediate cardiovascularoutcomes as well as long-term neurodevelopmental out-comes in both term and preterm infants. The results oflarge randomized clinical trials comparing delayed andimmediate clamping are needed to improve the lowquality of evidence now aggregated from multiple smalltrials with variable patient populations, few extremelypreterm infants, and variable interventions and outcomemeasures. The Cord Trial in the United Kingdom is

comparing clamping within 20 s to clamping after atleast 2 min among births < 32 weeks gestation [73]. TheAustralian Placental Transfusion Study compares clamp-ing within 10 s to clamping after 1 min with the infantheld below the level of the placenta. Comparative trialsof delayed cord clamping vs. cord milking can help de-fine the relative advantages of each method. Experimen-tal physiology studies of umbilical cord milking couldhelp further define the hemodynamics of that practice.Trials that specifically examine initiation of positive-pressure ventilation and/or continuous positive airwaypressure with the umbilical cord intact are underway.Packages of interventions that include other aspects ofphysiologic transition (thermal control, minimizing oxy-gen exposure and intubation, facilitating lung recruit-ment with positive-pressure ventilation, skin-to-skincontact for moderate and late preterm infants) should betested for their potential to achieve more-than-additivebenefit.

ConclusionsThe existing literature on delayed cord clamping andcord milking has consistently demonstrated benefit infacilitating placental transfusion. Improved physiologicstability in transition (blood pressure), reduced need fortransfusion, and lower incidence of intracranial haemor-rhage and necrotizing enterocolitis are valuable improve-ments in outcome. Several studies, of both delayed cordclamping and cord milking, have shown reduced needfor resuscitative interventions. Although these outcomesfall short of the overarching goals of improved neurode-velopmental outcome and reduced mortality in intensivecare settings, they offer promise. And, under circum-stances where medical support available to newly borninfants is severely limited, delayed cord clamping showsa positive relationship with decreased mortality.Recent experimental and population-based studies

highlight the interaction between onset of respirationsand timing of umbilical cord clamping. These havechanged the concept of delayed cord clamping from oneof a defined time interval only to one of facilitation ofphysiologic transition after birth. Before clear guidanceis available for clinicians on how best to facilitate thistransition, more research is needed. For the term infantwho breathes spontaneously, a delay of at least 2–3 minappears necessary to optimize circulatory transition andplacental transfusion. More evidence is needed about theinterventions that should be performed during delay incord clamping among infants who fail to breathe afterbirth. Preterm and very low birth weight infants as wellas infants who have experienced hypoxic-ischemicevents are of special interest, as they have generally beenexcluded from past studies. Data on umbilical cord

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milking are limited, and comparison between delayedcord clamping and cord milking is especially important.

Endnotes1Velpeau, AA. Traité elementaire de l'art des

accouchements; ou, Principes de tokologie et d'embryo-logie [Elementary treatise on the art of midwifery; or,Principles of tokology and embryology], 3rd Edition Eng-lish translation of the 1829 French text, Philadelphia:Lindsay & Blakiston, 1845, page 550, section 1209.

2Ibid, page 552, section 1213.3cIbid, page 553, section 1213.4Ibid, page 559, section 1222.5Ibid, page 551, section 1212.6Ibid, page 562-3, section 1227–9.

AbbreviationsACOG: American College of Obstetricians and Gynecologists; CPAP: Continuouspositive airway pressure; EIT: Electrical impedance tomography; MRI: Magneticresonance imaging; WHO: World Health Organization.

Competing interestsThe author declares that she has no competing interests.

Author’s contributionsThe author contributed to the conception and design of the review,reviewed and interpreted the data, prepared the manuscript, approved thefinal version to be published, and assumes responsibility for the contents.The author read and approved the final manuscript.

Author’s informationSN is Professor of Pediatrics in the Section of Neonatology of the Universityof Colorado School of Medicine and serves as a volunteer evidence reviewerfor the International Liaison Committee on Resuscitation.

AcknowledgementsNone.

Received: 25 June 2015 Accepted: 20 August 2015

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