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Postterm pregnancy

Author
Errol R Norwitz, MD, PhD, MBA
Section Editor
Charles J Lockwood, MD, MHCM
Deputy Editor
Vanessa A Barss, MD, FACOG

INTRODUCTION

The timely onset of labor and delivery is an important determinant of perinatal outcome. Both preterm and postterm births are associated with higher rates of perinatal morbidity and mortality than pregnancies delivering at term.

This topic will discuss maternal and fetal issues related to postterm pregnancy. Issues related to the postterm infant are reviewed separately. (See "Postterm infant".)

DEFINITION

Postterm pregnancy is defined as ≥42+0 weeks of gestation (≥294 days from the first day of the last menstrual period and ≥14 days from the estimated day of delivery) [1,2]. Postdates pregnancy and prolonged pregnancy are less commonly used synonyms for postterm pregnancy.

Of note, early term is defined as 37+0 to 38+6 weeks of gestation, full term is defined as 39+0 to 40+6 weeks of gestation, and late term is 41+0 to 41+6 weeks of gestation [1,3].

PREVALENCE

In the United States in 2015, birth certificate data indicated that 0.40 percent of pregnancies delivered at ≥42 weeks and 6.5 percent delivered at 41 weeks [4]. A study of birth rates ≥42 weeks in 13 European countries observed a wide range across the continent: from 0.4 and 0.6 percent in Austria and Belgium to 7.5 and 8.1 percent in Sweden and Denmark [5]. Variations in prevalence are likely due to the factors discussed below.

                 
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Literature review current through: Sep 2017. | This topic last updated: Sep 26, 2017.
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