Clinical Practice Guidelines Antenatal Care — Module II
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- Incidence of prolonged pregnancy
- Risks associated with prolonged pregnancy
- Options in prolonged pregnancy
- Summary of the evidence
- Surveillance in prolonged pregnancy
- Discussing prolonged pregnancy
- Practice summary: prolonged pregnancy
10.4Prolonged pregnancyIdentification 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. BackgroundThe 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 pregnancyThe 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 pregnancyPerinatal: The perinatal mortality rate (stillbirths plus early neonatal deaths) of 2–3/1,000 births at 40 weeks of gestation approximately doubles by 42 weeks to 4–7 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).
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 pregnancyPolicies 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 evidenceSweeping the membranesProcedures 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 2005). Recommendation 33 Grade C Consider offering membrane sweeping to women scheduled for formal induction of labour for prolonged pregnancy.
It may be advisable to avoid membrane sweeping before 40 weeks or in women at greater risk of Group B streptococcus. AcupunctureA 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 pregnancyIncreased 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. There is a lack of high-level evidence on surveillance between 41 and 42 weeks. Assessments may include cardiotocography, ultrasound scan to assess amniotic fluid volume, 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). Compared to using amniotic pool depth, using the amniotic fluid index increases the rate of diagnosis of oligohydramnios and the rate of induction of labour, without improvement in peripartum outcomes (Nabhan & Abdelmoula 2009). Practice point y Women should be advised to be vigilant of a change (reduction) in fetal movements between 41 and 42 weeks. Practice point z From 41 weeks, it may be reasonable to offer twice weekly cardiotocography and ultrasound to assess amniotic fluid index for surveillance of fetal well-being. Increased antenatal surveillance from 42 weeks gestation is recommended in the United Kingdom (NICE 2008) and the United States (ACOG 2004). For example ultrasound assessment of amniotic fluid volume and cardiotocography are used to evaluate fetal well-being. However, adverse fetal outcome in late pregnancy is not always predicted by these investigations and the relative risks and benefits of further prolonging the pregnancy should be evaluated in each case. Again, it is important that women are advised to report any changes in fetal movements.
InductionA 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 pregnancyAdvice 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’ labour; 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 ). 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).
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