Prolonged pregnancy

Prolonged pregnancy is defined as a pregnancy lasting more than 294 days (i.e. 42 weeks’ gestation). Measurement of the crown-rump length during a first trimester ultrasound is a reliable method of estimating gestation and is relied upon to define prolonged pregnancy. Prolonged pregnancy is recognised as a high-risk problem but the aetiology remains unknown. It is associated with increased adverse outcome for both the mother and the fetus. Perinatal morbidity and mortality are significantly increased and, for that reason, most obstetric units offer routine induction of labour between 41 and 42 weeks of gestation to minimise the adverse perinatal risks. However, there is no clear evidence about the optimum time to deliver. The alternative approach of expectant management with serial fetal surveillance, whilst awaiting the onset of spontaneous labour, has been advocated. The optimal method and timing of such fetal surveillance have not yet been established, but current NICE guidelines suggest twice-weekly cardiotocography and ultrasound estimation of maximum amniotic pool depth from 42 weeks gestation. Resources and maternal wishes must be considered when managing a prolonged pregnancy.