Postterm pregnancy

Abstract

Postterm pregnancy is a pregnancy that extends to 42 weeks of gestation or beyond. Fetal, neonatal and maternal complications associated with this condition have always been underestimated. It is not well understood why some women become postterm although in obesity, hormonal and genetic factors have been implicated. The management of postterm pregnancy constitutes a challenge to clinicians; knowing who to induce, who will respond to induction and who will require a caesarean section (CS). The current definition and management of postterm pregnancy have been challenged in several studies as the emerging evidence demonstrates that the incidence of complications associated with postterm pregnancy also increase prior to 42 weeks of gestation. For example the incidence of stillbirth increases from 39 weeks onwards with a sharp rise after 40 weeks of gestation. Induction of labour before 42 weeks of gestation has the potential to prevent these complications; however, both patients and clinicians alike are concerned about risks associated with induction of labour such as failure of induction and increases in CS rates. There is a strong body of evidence however that demonstrates that induction of labour at term and prior to 42 weeks of gestation (particularly between 40 & 42 weeks) is associated with a reduction in perinatal complications without an associated increase in CS rates. It seems therefore that a policy of induction of labour at 41 weeks in postterm women could be beneficial with potential improvement in perinatal outcome and a reduction in maternal complications.

Keywords: Body mass index; induction of labour; perinatal complications; postterm pregnancy; ultrasound.

Fig. 1. Perinatal mortality per 1000 ongoing pregnancies. Reproduced from BJOG Volume 105 (Hilder L, et al., 1998).

Fig. 2. Risk of Stillbirth by week of gestation (rate calculated per 1000 ongoing pregnancies) (Sutan et al. 2010).

Fig. 3. Relationship between stillbirth and gestational age (Yudkin et al., 1987).