SOGC Clinical Practice Guideline
No. 214-Guidelines for the Management of Pregnancy at 41+0 to 42+0 Weeks

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Abstract

Objective

To provide evidence-based guidelines for the management of pregnancy at 41+0 to 42+0 weeks.

Outcomes

Reduction of perinatal mortality associated with Caesarean section at 41+0 to 42+0 weeks of pregnancy.

Evidence

The Medline database, the Cochrane Library, and the American College of Obstetricians and Gynecologists and the Royal College of Obstetricians and Gynecologists, were searched for English language articles published between 1966 and March 2007, using the following key words: prolonged pregnancy, post-term pregnancy, and postdates pregnancy. The quality of evidence was evaluated and recommendations were made according to guidelines developed by the Canadian Task Force on Preventive Health Care.

Recommendations

  • 1.

    First trimester ultrasound should be offered, ideally between 11 and 14 weeks, to all women, as it is a more accurate assessment of gestational age than last menstrual period with fewer pregnancies prolonged past 41+0 weeks (I-A).

  • 2.

    If there is a difference of greater than 5 days between gestational age dated using the last menstrual period and first trimester ultrasound, the estimated date of delivery should be adjusted as per the first trimester ultrasound (I-A).

  • 3.

    If there is a difference of greater than 10 days between gestational age dated using the last menstrual period and second trimester ultrasound, the estimated date of delivery should be adjusted as per the second trimester ultrasound (I-A).

  • 4.

    When there has been both a first and second trimester ultrasound, gestational age should be determined by the earliest ultrasound (I-A).

  • 5.

    Women should be offered the option of membrane sweeping commencing at 38 to 41 weeks, following a discussion of risks and benefits (I-A).

  • 6.

    Women should be offered induction at 41+0 to 42+0 weeks, as the present evidence reveals a decrease in perinatal mortality without increased risk of Caesarean section (I-A).

  • 7.

    Antenatal testing used in the monitoring of the 41- to 42-week pregnancy should include at least a non-stress test and an assessment of amniotic fluid volume (I-A).

  • 8.

    Each obstetrical department should establish guidelines dependent on local resources for scheduling of labour induction (I-A).

Introduction

This document reflects emerging clinical and scientific advances on the date issued, and is subject to change. The information should not be construed as dictating an exclusive course of treatment or procedure to be followed. Local institutions can dictate amendments to these opinions. They should be well-documented if modified at the local level. None of these contents may be reproduced in any form without prior written permission of the publisher.

Women have the right and responsibility to make informed decisions about their care in partnership with their health care providers. In order to facilitate informed choice women should be provided with information and support that is evidence based, culturally appropriate and tailored to their needs. The values, beliefs and individual needs of each woman and her family should be sought and the final decision about the care and treatment options chosen by the woman should be respected.

The World Health Organization defines a post-term pregnancy as one that has extended to or beyond 42 weeks (294 days) of gestation.1 In 1997, the SOGC published clinical practice guidelines recommending that women with an uncomplicated pregnancy who reach 41 to 42 weeks' gestation should be offered elective delivery.2

Sue-A-Quan et al. undertook a Canadian study to examine trends over time in the rates of induction in post-term pregnancies.3 The proportion of births occurring at 41 weeks' gestation increased significantly from 11.9% in 1980 to 16.3% in 1995, and the proportion of births occurring at 42 weeks or more decreased significantly from 7.1% in 1980 to 2.9% in 1995. The authors reported that the rate of labour induction increased significantly between 1980 and 1995 among women delivering at 41 or more weeks' gestation, which indicates that the guidelines are, for the most part, being followed. The stillbirth rate was also examined in the study by Sue-A-Quan and colleagues. Interestingly, the stillbirth rate among deliveries at 41 or more weeks' gestation decreased significantly from 2.8/1000 total births in 1980 to 0.9/1000 total births in 1995 (P < 0.001).

Concern about increased risk to the post-term (−42 weeks) fetus has existed since the early to mid 1900s.4 Increased PMRs for the post-term fetus have been reported in descriptive studies.4, 5 However, these studies did not exclude all high-risk pregnancies or fetuses with congenital anomalies. Older descriptive studies that did correct for congenital anomalies did not find any difference in PMRs for post-term infants.6, 7 More recent database studies have demonstrated an increasing risk of stillbirth with advancing gestational age.8, 9, 10, 11 However, a Canadian database study did not demonstrate an increased post-term PMR.12 Other obstetrical and perinatal complications that were found to be higher in post-term pregnancies in these nonrandomized studies include fetal distress, non-progression, operative delivery (both operative vaginal and Caesarean), macrosomia, shoulder dystocia, low Apgar scores, and meconium aspiration.12, 13, 14 A linear decline of umbilical artery pH from term has also been described.15 Kitlinski et al.15 collected data on singleton pregnancies planned for vaginal delivery after 37 completed weeks. They defined acidemia as a pH <7.10 and a gestational age-dependent acidemia as a pH <mean-2 SDs. Their data show that the mean umbilical cord arterial blood pH at birth decreases linearly with gestational age. The odds ratio trend curve for low pH according to the gestational age-dependent definition of <mean-2 SDs showed no linear association with gestational age but a significant increase after 42 weeks (OR 1.24; 95% CI 1.05–1.47). The odds ratio for pH <7.10 among infants born after 41 weeks 3 days was also significant at 1.48 (95% CI 1.26–1.72).

The RCT is the most reliable form of scientific evidence, as it is the best known design for eliminating biases that can compromise the validity of research. Controversy about the management of and the risks associated with the post-term pregnancy led to the performance of many RCTs designed to determine if induction before or at the start of the post-term period versus expectant management results in any difference in maternal or perinatal outcomes.

This document updates the 1997 SOGC Guideline.2 Its recommendations refer only to otherwise uncomplicated pregnancies at 41 to 42 weeks' gestation. This guideline reviews the following:

  • 1.

    Interventions to decrease the incidence of pregnancy beyond 41+0 weeks.

  • 2

    The evidence for induction of labour versus antenatal surveillance in an uncomplicated pregnancy at 41+0 to 42+0 weeks.

  • 3.

    The role of antenatal fetal surveillance in the uncomplicated pregnancy at 41+0 to 42+0 weeks.

Sources of information include Medline, the Cochrane Library, and guidelines from the American College of Obstetricians and Gynecologists and the Royal College of Obstetricians and Gynaecologists. The quality of evidence was evaluated and recommendations were made according to guidelines developed by the Canadian Task Force on Preventive Health Care (Table).16

Section snippets

Accurate Pregnancy Dating

Error is associated with pregnancy dating by LMP alone. If the gestational age is underestimated, prematurity may be misdiagnosed, and unnecessary obstetric interventions performed. However, overestimation of gestational age is more likely, increasing the risks of unnecessary induction of labour.

Dating gestational age with LMP alone assumes both accurate recall of the LMP and ovulation on the 14th day of the menstrual cycle. Error in estimating LMP is due to inaccurate patient recall, maternal

Labour Induction Versus Expectant Management at 41 Weeks

Nineteen trials randomizing women with uncomplicated pregnancies at 41 or more weeks' gestation to induction or expectant management with surveillance were identified.49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67 A recently published trial randomized women at 41 weeks and two days of gestation to induction or expectant management; however, the authors do not specify if the pregnancies are uncomplicated.68 Two of these trials are reported as abstracts only.50, 66 A

Fetal Surveillance in the 41 to 42 Week Pregnancy

Options for fetal surveillance include fetal movement counting, non-stress test, biophysical profile or modified biophysical profile (non-stress test plus amniotic fluid volume estimation), and contraction stress test. In each of the aforementioned randomized trials of labour induction, compared with expectant management of the post-term patient, some form of antenatal test of fetal well-being was used at varying frequencies.49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67

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      Although in some high-risk pregnancies, it may be necessary to induce labour at preterm (<37 weeks) or early term (37+0 to 38+6 weeks) gestations, whenever possible and safe, IoL should be deferred until after 39 weeks of gestation to optimize short- and long-term outcomes for mother and baby [1–5]. In the case of low-risk pregnancies, most national and international organizations currently recommend IoL at or after 41 weeks of gestation [6–10]. However, a well-conducted randomized controlled trial (RCT) [11], and meta-analyses of cohort studies [12] and RCTs [13] have recently highlighted the benefits of IoL under 40 weeks of gestation, even in the absence of a medical indication.

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      There is strong evidence that continuation of pregnancies beyond 41–42 weeks of gestation, even in the absence of maternal and foetal risk factors, is associated with increased perinatal mortality and morbidity [15]. IoL between 41 and 42 weeks of gestation to prevent these complications, is therefore supported by most clinical practice guidelines [16–18]. There is a positive correlation between obesity and post-term pregnancy [19–22].

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      Women are not routinely involved in the decision making process which implicates unmet expectations and preferences [7]. However, guidelines recommend that women should be offered an IOL somewhere between 41 and 42 weeks gestation, and in a majority of the existing guidelines it is emphasised that the timing of IOL should be decided after discussing the management options and women's preferences in a process of shared decision making [8–11]. According to Elwyn et al. shared decision making is defined as “a dialogue between the patient (woman) and health care professional where women are supported to consider options in order to achieve informed preferences using the best available evidence”.

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    This guideline was peer-reviewed by the SOGC's Clinical Practice - Obstetrics Committee in May 2016, and has been reaffirmed for continued use until further notice.

    This guideline was prepared by the Clinical Practice Obstetrics Committee and reviewed by the Maternal Fetal Medicine Committee and reviewed and approved by the Executive and Council of The Society of Obstetricians and Gynaecologists of Canada.

    Clinical Practice Obstetrics Committee: Dean C. Leduc, MD (Chair), Ottawa, ON; Charlotte Ballermann, MD, Edmonton, AB; Anne Biringer, MD, Toronto, ON; Martina Delaney, MD, St. John's, NL; Loraine Dontigny, MD, Lasalle, QC; Thomas P. Gleason, MD, Edmonton, AB; Lily Shek-Yn Lee, RN, Vancouver, BC; Marie-Jocelyne Martel, MD, Saskatoon, SK; Valérin Morin, MD, Cap-Rouge, QC; Joshua Nathan Polsky, MD, Windsor, ON; Carol Rowntree, MD, Sundre, AB; Debra-Jo Shepherd, MD, Regina, SK; Kathi Wilson, RM, Ilderton, ON. Disclosure statements have been received from all members of the committee.

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