Post-term Pregnancy - Surveillance Strategies

Dr. Yasir Katib

MBBS, FRCSC, Perinatologist

Definitions

• Post mature

• Post dates

• Post-term

• Prolonged

Definitions

Post termPost term• Refers to a pregnancy that has extended to or

beyond a gestational age of 42.0 weeks or 294 days from the first day of the LMP

• Postterm pregnancy is associated with increased perinatal mortality and morbidity

Incidence

Incidence

Depends upon the patient population

1.Percentage of primigravid women

2.Women with pregnancy complications

3.Ultrasound assessment of GA

4.Frequency of spontaneous preterm birth

Incidence

Incidence • In the United States, approximately 10% (range 3

to 14 percent) of all singleton pregnancies continue beyond 42 weeks of gestation

WHO (1977), FIGO (1976)

• 4% (2 to 7 percent) continue beyond 43 completed weeks in the absence of obstetric intervention

Definitions

• “Postdates” : the real issue is “post-what dates?”

• “Post-term” or “prolonged” pregnancy are the preferred expressions for extended pregnancies

Incidence• limited reliability with LMP to determine

accurate post-term incidence– variations in timing of ovulation– irregular cycles– use of oral contraceptives

• when early ultrasound dating used in conjunction to LMP, incidence of post-term decreased from 10 % (LMP alone) to 3% (LMP + U/S) (Reuss et. al 1995)

Etiology

• The etiology of abnormal prolongation of gestation is not well understood (theories)

1.Hypoplasia of the fetal adrenal gland with or without anencephaly

2.Placental sulfatase deficiency

3.Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency

Morbidity and Mortality

• Increase mortality > 42 weeks gestation

• evidence from studies done looking outcome of post-term pregnancies prior to availability of intervention methods

Perinatal mortality in late pregnancy according to gestational age in Sweden 1943-1952 compared with 1977-1978. Logarithm scale is used for convenience in depiction. (Adapted from Bakketeig and Bergsjø, 1991, and Lindell, 1956.)

TABLE 1 PERINATAL DEATHS, EXCLUDING INFANTS WITH MALFORMATIONS, INSINGLETON BIRTHS AT 40, 41, AND 42 WEEKS AT PARKLAND HOSPITAL, 1993–1994

Gestational Age

Outcomea 40 wks 41 wks 42 wks

Pregnancies 7089 4995 3582Inductions (%) 317 (5) 301 (6) 865 (24)Stillbirths 8 5 3Neonatal deaths 0 0 2b

Perinatal deaths 8 (1.1) 5 (1.0) 5 (1.4)(per 1000)

a Includes women without prenatal care.b One neonatal death due to group B streptococcal sepsis.

TABLE 3 OUTCOMES IN POSTTERM PREGNANCIES (42 WEEKS OR GREATER) COMPARED WITH PREGNANCIES DELIVERED AT 40 WEEKS

40 Weeks Post-term(n = 8135) (n = 3457)

Factor a (%) (%)

Meconium 19 27Oxytocin induction 3 14Shoulder dystocia 8 18Cesarean delivery 0.7 1.3Macrosomia (> 4500 g) 0.8 2.8Meconium aspiration 0.6 1.6

a For all comparisons between 40- and 42-week groups, P < 0.05.

From Eden RD, Seifert LS, Winegar A, Spellacy WN. Perinatal characteristics of uncomplicated

postdate pregnancies. Obstet Gynecol. 69:296, 1987.

Macrosomia

• Complications associated with fetal macrosomia include

1.prolonged labor

2.cephalopelvic disproportion

3.shoulder dystocia with resultant risks of orthopedic (eg, clavicular fractures) or neurologic injury (eg, brachial plexus palsy)

IUGR

• Poor intrauterine growth are at increased risk

1.Umbilical cord compression from oligohydramnios

2.Nonreassuring fetal antepartum or intrapartum assessment

3.Cesarean delivery

Dysmaturity syndrome

• Approximately 20%of postterm fetuses have a syndrome of fetal dysmaturity

1.long, thin, malnourished infant

2.Meconium staining

3.Peeling skin

4.Chronic intrauterine growth restriction from uteroplacental insufficiency

Postmature infant delivered at 43 weeks’ gestation. Thick, viscous meconium coated the desquamating skin. Note the long, thin appearance and wrinkling of the palms of the hands.

Induction vs. Surveillance

• Several studies debate routine induction vs. surveillance

• Hannah (1992) – Canadian trial showed routine induction reduced

risk of perinatal death after 41 weeks, and not associated with increase risk of Caesarean section

– cost analysis (Goeree 1995) showed induction less expensive than serial monitoring

Induction vs.. Surveillance

• NICH 1994– American study showed that active labour

induction was not associated with improved outcome when compared to expectant management (at 41 weeks)

• thus either induction or expectant management acceptable

Induction vs.. Surveillance

• No evidence to support elective induction or serial antenatal monitoring for uncomplicated pregnancy from 39-40 6/7 weeks

Surveillance Methods

• Biochemical markers– Plasma or urine estrogen– Human Placental Lactogen– Placental proteins

no evidence to demonstrate benefit as antenatal surveillance for fetal well being in post-term pregnancies

Surveillance Methods

• Non-invasive– Fetal movement counts– Non stress test (Cardiotocography)– Biophysical Profile – Amniotic Fluid Volume estimates– Doppler Ultrasound

Surveillance Methods

• Others– Oxytocin challenge test / Contraction stress test– Amniocentesis

• Knox et al (1979)– meconium detected by amniocentesis associated with

intrapartum fetal distress; however induction of labour did not improve outcome

Surveillance Methods• NST

– False-normal Non-stress Tests (Smith et al.1987)

• fetal death within 7 days of normal non-stress tests

• most common indication for testing was prolonged pregnancy

• mean interval between test and death was 4 days, range of 1-7 days

• single most common autopsy finding: meconium aspiration

• investigators concluded that the non-stress test not adequate to preclude an acute asphyxial event

• other biophysical characteristics might be beneficial adjuncts: For example, assessment of amniotic fluid volume

• high false negative rates also reported by Miyazaki & Miyazaki (1981)

Surveillance Methods

• Ultrasound assessment of amniotic fluid– increased incidence of fetal compromise with

oligohydramnios in post-term pregnancies identification of decreased amniotic fluid

may identify post-term fetus in jeopardy

Surveillance Methods

• Ultrasound Amniotic Fluid Estimates– qualitative (Crowley 1980)

• presence of amniotic fluid between fetal trunk and limbs or uterine wall

– quantitative• Largest single pocket method

• Amniotic Fluid Index

Amniotic Fluid Volume Estimates

• Largest Pocket measurements– usually measured in the vertical– in BPP, a score of 2 is given for the presence of

a 2x2 amniotic fluid pocket– studies of AFV estimation have had different

lower limits ranging from 1-3cm (Manning 1980, Chamberlain 1984,Crowley 1984, Phelan 1985, Bochner 1987)

Amniotic Fluid Volume Estimate

– studies show that AFV may be effective discriminatory test in post-term pregnancy (Crowley 1984, Phelan 1985, Manning 1980)

– normal AFV does not preclude absence of adverse outcome

Amniotic Fluid Volume Estimate

• Amniotic Fluid Index– first proposed by Phelan (1986) and Rutherford

et al (1987)– summation of vertical pockets in four quadrants– table of gestational age-dependent norm of AFI

(Moore 1990); e.g. after 41weeks lower limit is 67 mm.

Amniotic Fluid Volume Estimate

• AFV vs. AFI

which is better???

Doppler ultrasound

• Fetal application first reported by Fitzgerald and Drumm (1977)

• non-invasive technique that uses high-frequency sound to investigate blood flow by detecting change in frequency of reflected sound

Doppler Ultrasound

• Theoretically, in post-term pregnancy:– increasing placental ‘age’ with increasing

uteroplacental insufficiency – expect diminished uteroplacental flow,

increased vascular resistance in umbilical artery and compensatory increased fetal cerebral artery flow (as in IUGR)

Doppler Ultrasound

• Several small studies have reported conflicting results

• positive studies usually small (Devine et al 1994, Anteby et al, 1994) or have strict criteria which are not common e.g. Absent end diastolic flow (Pearce et al, 1991)

Doppler Ultrasound

• Negative studies show poor discrimination of potential fetal compromise (Guidetti 1987, Farmakides 1988)

• Zimmerman et al (1995) showed that Doppler of uterine artery had a sensitivity of 7% in predicting poor outcome

Doppler Ultrasound

• Thompson and Trudinger 1990:– Observations using placenta and mathematical

models – the larger the placenta (and its arterial

branches), the greater fraction of vessels need to be obliterated before RI becomes abnormal

– this may explain poor sensitivity of umbilical Doppler in post-term pregnancies

Clinical Practice Guidelines

• ACOG Practice Patterns (1997)– “Due to ethical and medico-legal concerns, it is

highly unlikely that any subsequent studies will include a no-monitoring group”

– “…antenatal surveillance has become a standard practice on the basis of universal acceptance”

Clinical Practice Guidelines

• ACOG Practice Patterns (1997)

– Antenatal surveillance should be initiated by 42 weeks of gestation (C:III)

– No single antenatal surveillance protocol for monitoring fetal well-being in a post-term pregnancy appears superior to another

Clinical Practice Guidelines

• SOGC Committee Opinion (1997)

1. Establish gestational age

2. For uncomplicated pregnancy, no evidence to support elective induction or commencement of serial antenatal monitoring at 39 to 40 6/7 weeks

Clinical Practice Guidelines

• SOGC Committee Opinion (1997):

3. Women who reach 41 to 42 weeks of gestation (uncomplicated pregnancies) should be offered elective delivery

4. Serial fetal surveillance should consist (as a minimum) of an ultrasound assessment of amniotic fluid volume twice weekly…other forms of monitoring may be added to this (BPP, NST and fetal movement count)