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Pregnancy Care Guidelines

62 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.

62.1 Background

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 estimate of the birth date (ACOG 2004; Briscoe et al 2005; Siozos & Stanley 2005; Caughey et al 2008b; Mandruzzato et al 2010).

62.1.1 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 Chapter 20) 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).

62.1.2 Risks associated with prolonged pregnancy

  • Perinatal: 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
    • 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)
    • potential harms from unnecessary interventions resulting from false-positive test results associated with increased fetal surveillance (Divon & Feldman-Leidner 2008).

62.2 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).

62.2.1 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 to 0.74) and 42 weeks (RR: 0.28; 95%CI: 0.15 to 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

  • Grade C
  • 61

Consider offering membrane sweeping to women scheduled for formal induction of labour for prolonged pregnancy.

Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW

Recommendation

  • Practice point
  • KKK

It may be advisable to avoid membrane sweeping before 40 weeks or in women at greater risk of Group B streptococcus.

Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW

62.2.2 Acupuncture

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).

62.3 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.

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 (Morriset 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).

Recommendation

  • Practice point
  • LLL

Women should be advised to be vigilant of a change (reduction) in fetal movements between 41 and 42 weeks.

Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW

Recommendation

  • Practice point
  • MMM

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. 

Approved by NHMRC in June 2014; expires June 2019 UNDER REVIEW

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 wellbeing. 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.

62.4 Induction

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 to 0.88), meconium aspiration syndrome (RR 0.50; 95%CI 0.34 to 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).

62.5 Discussing prolonged pregnancy

Women should be provided with appropriate information and support to assist them in making an informed choice between scheduled induction for a prolonged pregnancy or monitoring without induction (or delayed induction). This 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
  • if pregnancy is prolonged, additional surveillance and management plans will be put into place following specialist consultation, to reduce the risk of adverse outcomes
  • the importance of contacting a health professional promptly if they have any concerns about decreased or absent fetal movements (see Section 22.2).

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).

62.6 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.

What

  • 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).

62.7 Resources

References

  • ACOG (2004) Management of Postterm Pregnancy. ACOG Practice Bulletin 55: American College of Obstetricians and Gynecologists.
  • Asher GN, Coeytaux RR, Chen W et al (2009) Acupuncture to initiate labor (Acumoms 2): a randomized, sham-controlled clinical trial. J Matern Fetal Neonatal Med 22(10): 843–48.
  • Bennett KA CJ, O’Shea P, Lacelle J, Hutchens D, Copel JA (2004) First trimester dating ultrasonography reduced the risk of induction of labour for postterm pregnancy. Am J Obstet Gynecol 190: 1077–81.
  • Boulvain M, Stan C, Irion O (2005) Membrane sweeping for induction of labour. Cochrane Database Syst Rev(1): CD000451.
  • Briscoe D, Nguyen H, Mencer M et al (2005) Management of pregnancy beyond 40 weeks’ gestation. Am Fam Physician 71(10): 1935–41.
  • Caughey AB, Nicholson JM, Washington AE (2008a) First- vs second-trimester ultrasound: the effect on pregnancy dating and perinatal outcomes. Am J Obstet Gynecol 198(6): 703 e1–6.
  • Caughey AB, Snegovskikh VV, Norwitz ER (2008b) Postterm pregnancy: how can we improve outcomes? Obstet Gynecol Surv 63(11): 715–24.
  • 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 weeks. J Obstet Gynaecol Can 30(9): 800–23.
  • Divon MY & Feldman-Leidner N (2008) Postdates and antenatal testing. Semin Perinatol 32(4): 295–300.
  • Doherty L & Norwitz ER (2008) Prolonged pregnancy: when should we intervene? Curr Opin Obstet Gynecol 20(6): 519–27.
  • 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.
  • Hill MJ, McWilliams GD, Garcia-Sur D et al (2008) The effect of membrane sweeping on prelabor rupture of membranes: a randomized controlled trial. Obstet Gynecol 111(6): 1313–19.
  • Hussain AA, Yakoob MY, Imdad A et al (2011) Elective induction for pregnancies at or beyond 41 weeks of gestation and its impact on stillbirths: a systematic review with meta-analysis. BMC Public Health 11 Suppl 3: S5.
  • Kashanian M, Akbarian A, Baradaran H et al (2006) Effect of membrane sweeping at term pregnancy on duration of pregnancy and labor induction: a randomized trial. Gynecol Obstet Invest 62(1): 41–44.
  • Khooshideh M, Izadi S, Shahriari A et al (2009) The predictive value of ultrasound assessment of amniotic fluid index, 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.
  • Lam H, Leung WC, Lee CP et al (2006) Amniotic fluid volume at 41 weeks and infant outcome. J Reprod Med 51(6): 484–88.
  • Li Z, Zeki R, Hilder L et al (2012) Australia’s Mothers and Babies 2010. Cat. no. PER 57. Sydney: Australian Institute for Health and Welfare National Perinatal Epidemiology and Statistics Unit.
  • Mandruzzato G, Alfirevic Z, Chervenak F et al (2010) Guidelines for the management of postterm pregnancy. J 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): 989–94.
  • Nabhan AF & Abdelmoula YA (2009) Amniotic fluid index versus single deepest vertical pocket: a meta-analysis of randomized controlled trials. Int J Gynaecol Obstet 104(3): 184-8.
  • NICE (2008) Antenatal Care. Routine Care for the Healthy Pregnant Woman. National Collaborating Centre for Women’s and Children’s Health. Commissioned by the National Institute for Health and Clinical Excellence. London: RCOG Press.
  • 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.
  • Yurdakok M (2011) Meconium aspiration syndrome: do we know? Turk J Pediatr 53(2): 121–29.
Last updated: 
20 November 2018