Risks associated with prolonged pregnancy

8.2 Prolonged pregnancy
Identification of prolonged pregnancy relies on accurate dating. True cases of prolonged pregnancy
require careful monitoring and management, to reduce the risk of adverse consequences for mother
and baby.
The standard definition of a prolonged pregnancy (also called post-term or post-dates) is gestation that
has lasted 42 weeks (294 days) or longer from the first day of the last normal menstrual period, or
14 days beyond the best obstetric estimate of the birth date (ACOG 2004; Briscoe et al 2005; Siozos & Stanley
2005; Caughey et al 2008b; Mandruzzato et al 2010).
Incidence of prolonged pregnancy
The reported frequency of prolonged pregnancy is approximately 5–10%, with the most common
reason being inaccurate dating (ACOG 2004; Caughey et al 2008a; Caughey et al 2008b; Delaney et al
2008; Doherty & Norwitz 2008). Routine ultrasound dating before 20 weeks gestation (see Section 7.1 of
Module I) significantly reduces the rate of prolonged pregnancy (Bennett KA 2004; Mandruzzato et al
2010) and the rate of induced labour (NICE 2008). Primiparity and previous prolonged pregnancy are
the most common identifiable causes of true prolonged pregnancy (ACOG 2004).
In Australia in 2010, 91.7% of women who gave birth did so at 37–41 completed weeks of gestation
(term) and 0.8% gave birth at 42 or more weeks gestation (this includes spontaneous or induced
labour and births by caesarean section) (Li et al 2012).
Risks associated with prolonged pregnancy
Perinatal: The perinatal mortality rate (stillbirths plus early neonatal deaths) at 40 weeks of gestation
approximately doubles by 42 weeks (4–7 deaths versus 2–3 deaths per 1,000 births) and increases
by 6-fold and higher at 43 weeks and beyond (Briscoe et al 2005). A higher risk of complications has
also been reported, including (Olesen et al 2003; Clark & Fleischman 2011; Yurdakok 2011):
— meconium aspiration syndrome;
— oligohydramnios (deficiency in amniotic fluid);
— central nervous system damage; and
— macrosomia and its associated complications (cephalopelvic disproportion, shoulder dystocia
and birth injury).
Maternal: reported maternal complications include:
— increased risk of prolonged labour, trauma to the pelvic floor, vagina and perineum due to
fetal macrosomia, caesarean section and postpartum haemorrhage (Olesen et al 2003; ACOG
2004; Briscoe et al 2005; Siozos & Stanley 2005; Caughey et al 2008b);
— anxiety, particularly if the woman perceives her prolonged pregnancy as high risk (ACOG 2004;
Heimstad et al 2007); and
— potential harms from unnecessary interventions resulting from false-positive test results
associated with increased fetal surveillance (Divon & Feldman-Leidner 2008).
Options in prolonged pregnancy
Policies vary on intervening in low-risk prolonged pregnancies. Offering labour induction after 41 weeks
is recommended in the United Kingdom (NICE 2008) and the United States (ACOG 2004). Factors to be
considered include the results of fetal assessment, favourability of the cervix (as assessed by Bishop’s
score), gestational age and the woman’s preferences, after discussion of available alternatives and
their risks and benefits (ACOG 2004; Norwitz et al 2007).
Summary of the evidence
Sweeping the membranes
Procedures for cervical ripening, such as membrane sweeping, may be of benefit in preventing
prolonged pregnancy, particularly in first pregnancies (Mandruzzato et al 2010). Membrane sweeping
involves the health professional introducing a finger into the cervical os and ‘sweeping’ it around the
circumference of the cervix during an vaginal examination, with the aim of separating the fetal
membranes from the cervix and triggering the release of prostaglandins (NICE 2008).
A systematic review (n=2,797) (Boulvain et al 2005) found an association between membrane sweeping,
and reduced frequency of pregnancy continuing beyond 41 weeks (RR: 0.59; 95%CI: 0.46–0.74) and
42 weeks (RR: 0.28; 95%CI: 0.15–0.50). The strength of the review was limited by small sample sizes and
heterogeneity of the studies and possible publication bias for some outcomes. Subsequent RCTs have
had inconsistent findings, with some confirming reduced prolonged pregnancy in low-risk women (de
Miranda et al 2006; Yildirim et al 2010) and others finding no significant effect on pregnancy duration,
particularly if performed before 41 weeks (Kashanian et al 2006; Hill et al 2008; Putnam et al 2011).
Membrane sweeping does not appear to increase the risk of maternal or fetal complications
(eg infection) (Boulvain et al 2005; de Miranda et al 2006; Yildirim et al 2010) but is associated with discomfort
during the procedure and other adverse effects (eg bleeding, irregular contractions) (Boulvain et al
Recommendation 24
Grade C
Before formal induction of labour for prolonged pregnancy, offer women a vaginal examination for
membrane sweeping.
A systematic review (n=212) (Smith & Crowther 2004) of studies with poor methodological quality, found
limited evidence regarding the clinical effectiveness of acupuncture for induction of labour. Four
additional small RCTS found that acupuncture was well tolerated but did not have significant clinical
effects (Harper et al 2006; Smith et al 2008; Asher et al 2009; Modlock et al 2010).
Surveillance in prolonged pregnancy
Increased fetal and maternal surveillance aims to identify risk of adverse outcomes and ensure timely
induction of labour if indicated (eg fetal compromise or oligohydramnios). There is no consensus about
optimal fetal surveillance (ACOG 2004) and specialist referral or consultation is likely to be required.
Assessments may include cardiotocography, ultrasound scan, amniotic fluid index (AFI), Doppler
and/or biophysical profile (Morris et al 2003; Lam et al 2006; Singh et al 2008; Khooshideh et al 2009; Grivell et al
2010). Limited evidence suggests that between 41+0 and 41+6 weeks gestation AFI is more useful than
ultrasound estimation of amniotic pool depth (Morris et al 2003) and cardiotocography or Doppler have
no significant benefit in predicting outcomes (Singh et al 2008).
Increased antenatal surveillance from 42 weeks gestation is recommended in the United Kingdom (NICE
2008) and the United States (ACOG 2004).
Consensus-based recommendation xvi
From 41 weeks, offer women ultrasound assessment of amniotic fluid volume.
Practice point m
From 42 weeks, offer women who choose expectant management increased antenatal monitoring
consisting of at least twice-weekly cardiotocography and assessment of amniotic fluid volume.
A recent Cochrane review (Gulmezoglu et al 2012) found that compared with a policy of expectant
management, a policy of labour induction was associated with lower rates of (all-cause) perinatal
deaths (RR: 0.31; 95%CI: 0.12–0.88), meconium aspiration syndrome (RR: 0.50; 95%CI: 0.34–0.73) and
caesarean section (RR: 0.89; 95%CI 0.81–0.97). Most studies adopted a policy of induction at 41 weeks.
Another systematic review with considerable overlap in the included studies had similar findings (Hussain
et al 2011).
Discussing prolonged pregnancy
Advice is ideally provided from the 38-week antenatal visit onwards, while a woman is still under the
care of a primary healthcare provider. This advice should include that:
most women go into labour spontaneously by 42 weeks;
the most common reason for a pregnancy becoming ‘prolonged’ is inaccurate dating;
there are risks associated with pregnancies that last longer than 42 weeks;
women with prolonged low-risk pregnancies may be offered membrane sweeping to ‘trigger’
membrane sweeping involves the health professional separating the membranes from the cervix as
part of a vaginal examination; it is safe but may cause discomfort and vaginal bleeding; and
if pregnancy is prolonged, additional surveillance and management plans will be put into place
following specialist consultation, to reduce the risk of adverse outcomes; and
the importance of contacting a health professional promptly if they have any concerns about
decreased or absent fetal movements (see Section Error! Reference source not found.).
Women should be appropriately counselled in order to make an informed choice between scheduled
induction for a prolonged pregnancy or monitoring without induction (or delayed induction)
(Gulmezoglu et al 2012).
Practice summary: prolonged pregnancy
When: At antenatal visits from 38 weeks onwards.
Who: Midwife; GP; obstetrician; Aboriginal and Torres Strait Islander Health Practitioner; Aboriginal and
Torres Strait Islander Health Worker; multicultural health worker.
Discuss the likelihood of prolonged pregnancy: Explain to the woman that pregnancy beyond
42 weeks is unlikely if dating is accurate.
Discuss why interventions may be offered: Explain that the risk of complications increases from
42 weeks gestation. Decisions about management are made after considering the risks and
benefits and taking the woman’s preferences into account.
Discuss the need for fetal surveillance: Explain that increased fetal monitoring is necessary from 41
weeks, to ensure that there are no risks to the baby from the pregnancy continuing.
Take a holistic approach: As well as the potential for women to experience anxiety if pregnancy is
prolonged, consider practical difficulties (eg when the woman has travelled to give birth or
arranged additional support around the estimated date of birth) and provide advice on relevant
community supports (eg available financial assistance).
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Clark SL & Fleischman AR (2011) Term pregnancy: time for a redefinition. Clin Perinatol 38(3): 557–64.
de Miranda E, van der Bom JG, Bonsel GJ et al (2006) Membrane sweeping and prevention of post-term pregnancy
in low-risk pregnancies: a randomised controlled trial. BJOG 113(4): 402–08.
Delaney M, Roggensack A, Leduc DC et al (2008) Guidelines for the management of pregnancy at 41+0 to 42+0
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Grivell RM, Alfirevic Z, Gyte GM et al (2010) Antenatal cardiotocography for fetal assessment. Cochrane Database
Syst Rev(1): CD007863.
Gulmezoglu AM, Crowther CA, Middleton P et al (2012) Induction of labour for improving birth outcomes for women
at or beyond term. Cochrane Database Syst Rev 6: CD004945.
Harper TC, Coeytaux RR, Chen W et al (2006) A randomized controlled trial of acupuncture for initiation of labor in
nulliparous women. J Matern Fetal Neonatal Med 19(8): 465–70.
Heimstad R, Romundstad PR, Hyett J et al (2007) Women's experiences and attitudes towards expectant
management and induction of labor for post-term pregnancy. Acta Obstet Gynecol Scand 86(8): 950–56.
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membranes: a randomized controlled trial. Obstet Gynecol 111(6): 1313–19.
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and its impact on stillbirths: a systematic review with meta-analysis. BMC Public Health 11 Suppl 3: S5.
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pregnancy and labor induction: a randomized trial. Gynecol Obstet Invest 62(1): 41–44.
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biophysical profile score, nonstress test and foetal movement chart for meconium-stained amniotic fluid in
prolonged pregnancies. J Pak Med Assoc 59(7): 471–74.
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Perinat Med 38(2): 111–19.
Modlock J, Nielsen BB, Uldbjerg N (2010) Acupuncture for the induction of labour: a double-blind randomised
controlled study. BJOG 117(10): 1255–61.
Morris JM, Thompson K, Smithey J et al (2003) The usefulness of ultrasound assessment of amniotic fluid in predicting
adverse outcome in prolonged pregnancy: a prospective blinded observational study. BJOG 110(11): 989–
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Norwitz ER, Snegovskikh VV, Caughey AB (2007) Prolonged pregnancy: when should we intervene? Clin Obstet
Gynecol 50(2): 547–57.
Olesen AW, Westergaard JG, Olsen J (2003) Perinatal and maternal complications related to postterm delivery: a
national register-based study, 1978-1993. Am J Obstet Gynecol 189(1): 222–27.
Putnam K, Magann EF, Doherty DA et al (2011) Randomized clinical trial evaluating the frequency of membrane
sweeping with an unfavorable cervix at 39 weeks. Int J Womens Health 3: 287–94.
Singh T, Sankaran S, Thilaganathan B et al (2008) The prediction of intra-partum fetal compromise in prolonged
pregnancy. J Obstet Gynaecol 28(8): 779–82.
Siozos C & Stanley KP (2005) Prolonged pregnancy. Curr Obstet Gynaecol 15: 73–79.
Smith CA & Crowther CA (2004) Acupuncture for induction of labour. Cochrane Database Syst Rev(1): CD002962.
Smith CA, Crowther CA, Collins CT et al (2008) Acupuncture to induce labor: a randomized controlled trial. Obstet
Gynecol 112(5): 1067–74.
Yildirim G, Gungorduk K, Karadag OI et al (2010) Membrane sweeping to induce labor in low-risk patients at term
pregnancy: a randomised controlled trial. J Matern Fetal Neonatal Med 23(7): 681–87.
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