PROLONGED PREGNANCY - EVALUATING GESTATION-SPECIFIC RISKS OF FETAL AND INFANT-MORTALITY

Objective To evaluate gestation-specific risks of stillbirth, neonatal and post-neonatal mortality. Design Retrospective analysis of 171,527 notified births (1989-1991) and subsequent infant survival at one yea r, from community child health records. Setting Notifications from mat ernity units in the North East Thames Region, London. Main outcome mea sures The incidence of births, stillbirths, neonatal and post-neonatal deaths at each gestation after 28 completed weeks. Mortality rates pe r 1000 total or live births and per 1000 ongoing pregnancies at each g estation were calculated. Results The rates of stillbirth at term (2.3 per 1000 total births) and post-term (1.9 per 1000 total births) were similar. When calculated per 1000 ongoing pregnancies, the rate of st illbirth increased six-fold from 0.35 per 1000 ongoing pregnancies at 37 weeks to 2.12 per 1000 ongoing pregnancies at 43 weeks of gestation . Neonatal and post-neonatal mortality rates fell significantly with a dvancing gestation, from 151.4 and 31.7 per 1000 live births at 28 wee ks, to reach a nadir at 41 weeks of gestation (0.7 and 1.3 per 1000 li ve births, respectively), increasing thereafter in prolonged gestation to 1.6 and 2.1 per 1000 live births at 43 weeks of gestation. When ca lculated per 1000 ongoing pregnancies, the overall risk of pregnancy l oss (stillbirth + infant mortality) increased eight-fold from 0.7 per 1000 ongoing pregnancies at 37 weeks to 5.8 per 1000 ongoing pregnanci es at 43 weeks of gestation. Conclusion The risks of prolonged gestati on on pregnancy are better reflected by calculating fetal and infant l osses per 1000 ongoing pregnancies. There is a significant increase in the risk of stillbirth, neonatal and post-neonatal mortality in prolo nged pregnancy. This study provides accurate data on gestation-specifi c risks of pregnancy loss, enabling pregnant women and their carers to judge the appropriateness of obstetric intervention.