Common Questions About Late-Term and Postterm Pregnancy



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Am Fam Physician. 2014 Aug 1;90(3):160-165.

This clinical content conforms to AAFP criteria for continuing medical education (CME). See the CME Quiz Questions.

  Patient information: A handout on this topic is available at http://familydoctor.org/familydoctor/en/pregnancy-newborns/labor-childbirth/pregnancy-what-to-expect-when-youre-past-your-due-date.html.

Author disclosure: No relevant financial affiliations.

Pregnancy is considered late term from 41 weeks, 0 days' to 41 weeks, 6 days' gestation, and postterm at 42 weeks' gestation. Early dating of the pregnancy is important for accurately determining when a pregnancy is late- or postterm, and first-trimester ultrasonography should be performed if clinical dating is uncertain. Optimal management of a low-risk, late-term pregnancy should consider maternal preference and balance the benefits and risks of induction vs. waiting for spontaneous labor. Compared with expectant management, induction at 41 weeks' gestation is associated with a small absolute decrease in perinatal mortality and decreases in other fetal and maternal risks without an increased risk of cesarean delivery. Although there is no clear evidence that antenatal testing beginning at 41 weeks' gestation prevents intrauterine fetal demise, it is often performed because the risks are low. When expectant management is chosen, most experts recommend beginning twice-weekly antenatal surveillance at 41 weeks with biophysical profile or nonstress testing plus amniotic fluid index (modified biophysical profile); induction may be deferred until 42 weeks if this surveillance is reassuring.

Postterm pregnancy is defined as that lasting beyond 294 days or 42 weeks' gestation. In 2009, nearly 6% of singleton births in the United States occurred at or beyond 42 weeks' gestation.1 More recently, attention has focused on the concept of late-term pregnancy, which is from 41 weeks, 0 days' to 41 weeks, 6 days' gestation.2 Late-term pregnancy is important because of the increasing fetal and maternal risks during this time. The clinical concerns surrounding late-term pregnancy include the risks and anticipated outcomes for expectant management vs. induction, the predictors of a successful induction (i.e., an induction that leads to a vaginal delivery), the role of antenatal surveillance, and the risk of failed induction followed by cesarean delivery.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation Evidence rating References

Labor induction at 41 weeks' gestation is associated with a small but significant reduction in perinatal mortality compared with expectant management (number needed to treat = 410).

A

19, 20

Labor induction at 41 weeks' gestation decreases the cesarean delivery rate compared with spontaneous labor at 42 weeks after expectant management (number needed to treat = 30).

A

19, 24, 25, 29, 37

Infants delivered at or beyond 41 weeks' gestation are at increased risk of meconium aspiration syndrome.

C

19, 20, 23, 24

Delivery beyond 42 weeks' gestation increases the maternal complications of postpartum hemorrhage, dystocia, and maternal infection (i.e., chorioamnionitis and endometritis). However, there is no difference in risk of maternal hemorrhage or infection at 41 weeks between expectant management and induction.

B

19, 21, 28, 29

Women with pregnancies lasting beyond 41 weeks' gestation should undergo twice-weekly antenatal testing until delivery.

C

8, 32


A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

View Table

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation Evidence rating References

Labor induction at 41 weeks' gestation is associated with a small but significant reduction in perinatal mortality compared with expectant management (number needed to treat = 410).

A

19, 20

Labor induction at 41 weeks' gestation decreases the cesarean delivery rate compared with spontaneous labor at 42 weeks after expectant management (number needed to treat = 30).

A

19, 24, 25, 29, 37

Infants delivered at or beyond 41 weeks' gestation are at increased risk of meconium aspiration syndrome.

C

19, 20, 23, 24

Delivery beyond 42 weeks' gestation increases the maternal complications of postpartum hemorrhage, dystocia, and maternal infection (i.e., chorioamnionitis and endometritis). However, there is no difference in risk of maternal hemorrhage or infection at 41 weeks between expectant management and induction.

B

19, 21, 28, 29

Women with pregnancies lasting beyond 41 weeks' gestation should undergo twice-weekly antenatal testing until delivery.

C

8, 32


A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.

BEST PRACTICES IN OBSTETRICS: RECOMMENDATIONS FROM THE CHOOSING WISELY CAMPAIGN

Recommendation Sponsoring organization

Do not schedule elective, non–medically indicated

The Authors

MARY WANG, MD, is an assistant clinical professor in the Department of Family and Preventive Medicine at the University of California, San Diego.

PATRICIA FONTAINE, MD, MS, is a senior clinical research investigator at the HealthPartners Institute for Education and Research in Bloomington, Minn.

Address correspondence to Mary Wang, MD, University of California, San Diego, 9333 Genesee Ave., #200, San Diego, CA 92121 (e-mail: mjw011@ucsd.edu). Reprints are not available from the authors.

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