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AOGS MAIN RESEARCH ARTICLE

Management of prolonged pregnancy by induction with aFoley catheter

HEIDI KRUIT1, OSKARI HEIKINHEIMO1, VELI-MATTI ULANDER1, ANSA AITOKALLIO-TALLBERG1,IRMELI NUPPONEN2, JORMA PAAVONEN1 & LEENA RAHKONEN1

1Department of Obstetrics and Gynecology, University of Helsinki and Helsinki University Hospital, Helsinki, and2Childrens Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland

Key words

Labor induction, Foley catheter, prolonged

pregnancy, cesarean delivery rate, nulliparous

women

Correspondence

Heidi Kruit, Department of Obstetrics and

Gynecology, Helsinki University Hospital,

Haartmaninkatu 2, 00029 HUS Helsinki,

Finland.

E-mail: [email protected]

Conflict of interest

The authors have stated explicitly that there

are no conflicts of interest in connection with

this article.

Please cite this article as: Kruit H,

Heikinheimo O, Ulander V-M, Aitokallio-

Tallberg A, Nupponen I, Paavonen J, et al.

Management of prolonged pregnancy by

induction with a Foley catheter. Acta ObstetGynecol Scand 2015; 94: 608614.

Received: 30 December 2014

Accepted: 4 March 2015

DOI: 10.1111/aogs.12632

Objectives. To describe labor outcomes in women with prolonged pregnancy

and induction of labor with a Foley catheter, as compared with women with

spontaneous onset of labor. Design. Retrospective study. Setting. Helsinki Uni-

versity Hospital. Sample. 553 women with uncomplicated prolonged pregnan-

cies between January 2011 and January 2012, divided into 303 women (54.8%)

with Foley catheter induction and 250 (45.2%) with spontaneous labor. Meth-

ods. Maternal and neonatal characteristics of women with uncomplicated sin-gleton pregnancy of 41+5 weeks of gestation were analyzed. Main outcome

measures. Cesarean delivery rates, maternal and neonatal morbidity.

Results. The cesarean delivery rate was 30.7% (n = 93/303) in women with

labor induction and 4.8% (12/250) in women with spontaneous onset of labor

(p < 0.001). The cesarean delivery rate was 37.3% (91/244) among nulliparous

women with labor induction and 8.7% (11/126) among women with spontane-

ous labor, a sixfold increased risk (odds ratio 6.2). Among parous women,

cesarean section rates were low and not significantly different (3.4% vs. 0.8%,

p = 0.2). There were no differences in maternal intrapartum or postpartum

infection rates or adverse neonatal outcomes between the groups. Conclu-

sions. Foley catheter induction of labor in prolonged pregnancy did not

increase maternal or perinatal morbidity compared with spontaneous onset oflabor but was associated with a considerably increased cesarean section rate,

particularly among nulliparous women.

Abbreviations: GBS, Group B Streptococcus agalactiae; IOL, induction of labor.

Introduction

The World Health Organization defines post-term preg-

nancy as one extending to 42+0 weeks (294 days) (1).

Post-term pregnancy occurs in approximately 5% of preg-

nancies, varying in reported frequency from 0.4 to 8.1%

in different countries (2). In Finland, 810% of all preg-

nancies extend beyond 41 weeks of gestation and the rate

of post-term pregnancy has ranged between 4.2 and 4.8%

during recent years (3,4). Post-term pregnancy is associ-

ated with maternal and fetal risks, raised rates of opera-

tive delivery, and increased perinatal mortality (5,6).

Key Message

Labor induction with Foley catheter in prolonged

pregnancy appears as safe as spontaneous labor in

terms of perinatal morbidity but is associated with a

high rate of cesarean delivery, particularly among nul-

liparous women. Given the major impact of the first

cesarean delivery on subsequent pregnancies, it is

important to optimize labor induction methods, not

least for nulliparous women.

2015 Nordic Federation of Societies of Obstetrics and Gynecology, Acta Obstetricia et Gynecologica Scandinavica 94 (2015) 608614608

A C TA Obstetricia et Gynecologica

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Post-term pregnancy is the most common indication for

labor induction (7). Nowadays, induction of labor (IOL)

is started before 42 weeks in many countries since several

clinical practice guidelines on the management of post-

term pregnancy recommend elective induction and deliv-

ery by 41 completed weeks (1,8,9). While induction rates

have increased, the rates of post-term pregnancy havedecreased (8).

There is a concern that rising rates of IOL may increase

cesarean deliveries (10,11). However, it has been debated

whether the increased cesarean section rates are related to

the IOL or to the indication(s) for induction. In a

recently published Norwegian study, only insignificant

increases in the cesarean section rate were seen after a

change to a more liberal induction policy for prolonged

pregnancies (12). Furthermore, in a recent meta-analysis

the cesarean section rate in term and post-term pregnan-

cies was lower among women with induced labor than in

women managed expectantly (13).

The Foley catheter method has been established for

IOL since it was first described in the early 1980s. Then,

it was used in conjunction with prostaglandin administra-

tion via the catheter (14). After 1990, additional studies

on the use of the Foley catheter for labor induction were

published. Recently, the Foley catheter has been shown to

result in a comparable vaginal delivery rate to that seen

following induction with prostaglandins in low-risk

women with an unfavorable cervical score at term

(15,16).

The aim of this study was to evaluate delivery outcomes

in prolonged pregnancies induced by Foley catheter.

Material and methods

This retrospective study of women with a prolonged

pregnancy of 41+5 gestational weeks between January

2011 and January 2012 (1 year) was conducted at the

Department of Obstetrics and Gynecology, Helsinki Uni-

versity Hospital, Finland. According to the departmental

management guidelines, all women with an uncompli-

cated prolonged pregnancy receive an appointment for an

antenatal visit in the maternity outpatient clinic at 41+5

weeks of gestation. The decision on IOL or expectant

management depends on an assessment of maternal andfetal wellbeing and on maternal preference. Fetal wellbe-

ing was examined by cardiotocography (non-stress test)

and ultrasonographic assessment of fetal growth, fetal

movements, and amniotic fluid volume (biophysical pro-

file). Where expectant management was chosen, IOL was

scheduled no later than 42+1 weeks (4 days later) if spon-

taneous labor had not commenced. Since 2010, the Foley

catheter has been the main method of labor induction in

our department (17).

A total of 798 women with an uncomplicated singleton

pregnancy 41+5 weeks of gestation were identified from

the hospital database during the study year. Duration of

pregnancy was defined by the fetal crown

rump length

measurement performed at the time of first trimester

ultrasound screening. We excluded 212 women with

breech presentation, a history of cesarean section or pre-

vious rupture of membranes in the current pregnancy

(Figure 1). Since we wanted to focus on Foley catheter

induction, a relatively new IOL method in our clinic at

the time, we also excluded women in whom other induc-

tion methods were used. The final database thus con-

tained 553 deliveries, including 303 women (54.8%) with

Foley catheter IOL and 250 women (45.2%) with sponta-

neous labor by 42+1 weeks of gestation. In all cases the

main indication for IOL was prolonged pregnancy. Thestudy protocol was approved by the local Ethics Commit-

tee (No. 268/13/03/03/2012) and the management of the

Hospital district of Helsinki and Uusimaa.

In Foley catheter induction a single balloon catheter

(Rusch 2-way Foley Couvelaire tip catheter size 22 Ch,

Spontaneous laborn= 250

Primary exclusion (n = 212):

Previous cesarean section n = 79Breech presentation n = 2

Amniotomy n = 70Prostaglandin n = 61

Study populationn= 798

Labor inductionn= 336

Primiparousn= 126

Multiparousn= 124

Primiparousn= 244

Multiparousn= 59

Secondary exclusion:Foley catheter +prostaglandin

n = 33

Figure 1. Flow chart of the study population.

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Teleflex Medical, Athlone, Ireland) was used. In 139

(45.9%) cases the catheter was inserted at gestational age

41+5, in 65 women (21.5%) at 41+6, in 83 (27.4%) at

42+0 and in 16 (5.2%) at 42+1 weeks. Before inserting the

catheter, a Bishop score was determined (18). At com-

mencement of IOL all the women had unfavorable cervi-

cal scores (Bishop score 6). The catheter was introducedinto the endocervix and towards the space between the

amniotic membrane and the lower uterine segment. The

balloon reservoir was inflated with 4050 mL of saline

and retracted so that it rested on the internal os. Light

traction was applied and the catheter was taped on to the

inner aspect of the thigh. Fetal monitoring for a mini-

mum of 20 min was continued. After spontaneous expul-

sion of the balloon, amniotomy was performed if the

Bishop score was 6. If spontaneous expulsion of the Fo-

ley catheter did not occur within 24 h, the balloon was

removed. If the cervix remained unripe with a Bishop

score 20 9 109/L. At least two of these criteria had to

be met, combined with administration of antibiotics.Postpartum infection diagnoses included endometritis (by

the above criteria), wound infection, mastitis, urinary

tract infection and puerperal fever of unknown origin.

Neonatal infections were categorized into blood culture

positive sepsis, clinical sepsis, and suspected sepsis. Neo-

natal clinical sepsis was defined as a blood culture nega-

tive infection with symptoms and signs consistent with

sepsis (such as respiratory distress, apnea, tachycardia,

poor capillary perfusion, low blood pressure, fever, hypo-

or hyperglycemia, irritability, feeding problems, lethargy

and convulsions), abnormal blood values (such as ele-

vated levels of the C-reactive protein, leukocytosis or leu-

kopenia, increased neutrophil precursors and

thrombocytopenia) and positive response to a minimum

of 5 days of antibiotic treatment. The cases defined as

suspected sepsis had to have at least one symptom and

one abnormal laboratory test value, and a positive

response to antibiotic treatment.

All calculations were carried out using the Microsoft

Statistical Package for Social Sciences for Windows v18.0

(SPSS Inc., Chicago, IL, USA). Categorical variables were

compared by the chi-squared and Fishers exact tests when

appropriate. Data with continuous variables were analyzed

by the t-test when the data followed normal distribution

and by a Mann

Whitney U-test if this was not the case.We used univariate logistic regression to estimate relative

risks represented by odds ratios with 95% confidence

intervals. A p-value < 0.05 was considered significant.

Results

The characteristics of the study population are shown in

Table 1. The women with induced labor were more often

nulliparous (p < 0.001) and more often had an extended

gestational age of 42 weeks at the start of IOL

(p < 0.001) compared with women with spontaneous

labor onset at or after 41+5 weeks. The medians of gesta-

tional weeks at the start of IOL and spontaneous labor

were, however, similar in both groups: 41.9 (range 41.7

42.3) and 41.9 (range 41.742.6).

Maternal outcomes are shown in Table 2. The nullipa-

rous, but not parous, women with IOL more often

received prophylactic antibiotics and epidural or spinal

analgesia than women with spontaneous labor onset did

(p < 0.001, p = 0.03, respectively). Oxytocin augmenta-

tion was more common in IOL cases than among women


Labor induction in prolonged pregnancy H. Kruitet al.

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with spontaneous labor, among both nulliparous and par-

ous women (p < 0.001 and p < 0.02, respectively).

The overall cesarean delivery rate was 30.7% (n = 93)

in women with IOL and 4.8% (n = 12) among women

with spontaneous labor (p < 0.001). Differences in the

cesarean delivery rates were observed in nulliparous

women (37.3 vs. 8.7%, p < 0.001) but not among the

parous women (3.4 vs. 0.8%, p = 0.2). The odds ratio for

cesarean delivery among nulliparous women was 6.2

[95% confidence interval (CI) 3.212.1]. The indications

Table 1. Characteristics of the study population.

Foley catheter induction

(n = 303)

Spontaneous labor

(n = 250)

p-valuen % n %

Maternal age 35 years 65 21.5 70 28.0 0.07

Nulliparous 244 80.5 126 50.4

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for cesarean delivery did not differ between the groups of

nulliparous women. No difference was found in the rates

of postpartum hemorrhage between the groups of nullip-

arous or parous women (Table 2).

The Bishop score was 3 in 50.4% (n = 119) in the

nulliparous women and in 23.5% (n = 20) in women

with spontaneous labor (p < 0.001). The corresponding

figures among parous women were 50.9% (n = 29) and20.5% (n = 18) (p < 0.001).

Of the nulliparous women who had a Bishop score 3

at IOL, 43.8% (49/112) had a cesarean delivery compared

with 31.2% of those with a Bishop score 4 (39/125)

(p = 0.04). Of parous women with a Bishop score 3,

only two of 24 had cesarean delivery, whereas all parous

women with a higher score delivered vaginally. The rate

of cesarean delivery following IOL of labor did not differ

between obese and women with normal weight (38.2 vs.

29.7%, p = 0.31). There were no differences in the overall

intrapartum or postpartum infection rates between

women with IOL and women with spontaneous labor

onset. However, postpartum endometritis occurred only

following IOL (Table 2). No cases of blood culture-posi-

tive maternal sepsis were found. Of the nulliparous

women with intrapartum infection, 66.7% (10/15) of the

induced and 33.3% (1/3) of the spontaneous labor group

had had a cesarean delivery.

No differences were found in the adverse neonatal out-

comes (low Apgar score, low umbilical artery pH or low

base excess value), NICU or neonatal unit admissions

between the induced and spontaneous labor groups

(Table 3). There were more neonatal infections diagnosed

after IOL than after spontaneous labor. After excluding

cases of suspected neonatal sepsis and comparing only

clinical neonatal sepsis cases, there was no difference

between the two groups (p = 0.43). No blood culture-

positive cases were found. Of neonatal infections among

nulliparous women, 6/19 followed vaginal delivery and 13(68.4%) cesarean delivery. All parous women whose neo-

nate was diagnosed with infection (n = 4) had delivered

vaginally. Overall, GBS was tested on only 11.2%

(n = 62) of the women.

Of the 33 women (9.8%) with a Bishop score 4500 g) 8 3.3 4 3.2 0.96 3 5.1 9 7.3 0.58

Apgar 1 min

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by a selection bias whereby more women with post-term

pregnancy ended up in the induction group and where

there was skewness towards a higher proportion of nullip-

arous women in group induced by Foley catheter. Large

randomized controlled trials on post-term pregnancy

management have been published (19) but we focused on

a narrow time frame (gestational length 41+5

to42+1 weeks). The value of this study lies in the use of that

approach, which offsets to some extent our lack of power.

Alexander et al. (20) have demonstrated a 40% increase

in the cesarean delivery rate (from 14 to 19%) following

IOL compared with spontaneous labor at 41 weeks.

Overall, for induction at term, cesarean delivery rates

seem to increase three- to eightfold regardless of whether

induction is mechanical or pharmacological (21,22). In

our study the rate was sixfold higher among nulliparous

women. This is of concern given the overall 14% cesarean

rate among women aiming for vaginal delivery in our

hospital during 2012. However, some recent studies have

shown that the risk of cesarean delivery in prolonged and

post-term gestations may be lower among women with

induced labor compared with those managed expectantly

(8,12,13). The reasons for the different results are not

known but could depend on the induction method used

and the definition of prolonged pregnancy.

Nulliparity and obesity increase the risk for prolongation

of pregnancy, but they are also independent risk factors for

cesarean delivery after induced labor (20,2325). Low

Bishop scores are associated with high rates of induction

failure and operative delivery (11,26,27), also seen in our

study. The cesarean delivery rate was even higher, almost

50%, among the women in whom there was sequential useof the Foley catheter and intravaginal misoprostol.

Cervical ripening was assessed using the Bishop score,

which was originally derived from parous women (18).

We used a score of 6 as a cut-off for the use of amniot-

omy and oxytocin augmentation. A more modern con-

cept would be a Bishop score 8 (28). The exact

mechanism of cervical ripening is not completely under-

stood. Studies have proposed that it relates to a reduction

in collagen density coupled to remodeling of the collagen

fibers (29). A recent study suggests that cell-free fetal

DNA initiates an inflammation process and with that cer-

vical ripening, leading to onset of labor (30). What hap-

pens with the use of a Foley catheter is not known.

The most common cesarean delivery indication follow-

ing IOL was failure to progress (failed induction and

labor arrest), as also noted previously (15,27,31).

In previous studies, as shown in a recent Cochrane

review, IOL by means of Foley catheter has not been

associated with increased rates of maternal infection

(15,16,32), as also found in this study, but contrasting

results have also been described (33). Likewise, clinical

neonatal infectious morbidity was not more common fol-

lowing induced labor, as shown previously (15). IOL itself

has, however, been linked to increased admissions to neo-

natal unit (34).

Our key finding was the high rate of cesarean delivery

among nulliparous women undergoing IOL by Foley

catheter between 41+5

and 42+1

weeks of gestation. Giventhe major impact that the first cesarean delivery has on

subsequent pregnancies, there is a need to optimize labor

induction among nulliparous women.

Funding

This study was supported by a grant from the Finnish

Medical Society Duodecim and Helsinki University Cen-

tral Hospital Research Funds.

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