BACKGROUND: A previous post-term pregnancy is thought to influence the gestation of a subsequent pregnancy. Adverse maternal and perinatal outcomes are associated with post-term pregnancy and routine induction of labour by 42+0 weeks is advised to reduce these complications.
OBJECTIVE: To determine the recurrence rate of a post-term pregnancy and the need for repeat induction of labour.
METHODS: This observational cohort study featured women with a first and second singleton pregnancy, based on data recorded in the Aberdeen Maternity and Neonatal Databank (1986-2012). Term and post-term pregnancies were defined as ≥37+0 - 40+6 and ≥41+0 weeks, respectively. The exposure was a post-term pregnancy and the control a term pregnancy. Logistic regression was used to assess post-term recurrence and repeat induction of labour.
RESULTS: The study population consisted of 25,669 women with 33% of the women delivering post-term in their first pregnancy. In these women, the rate of a subsequent post-term pregnancy was 35.7% compared to 18.6% for women with an initial term pregnancy (adjusted odds ratio (aOR) 2.27, 95% confidence interval (CI) 2.11-2.44). Compared to women who had spontaneous term deliveries in both pregnancies, women who were induced post-term in the second pregnancy had increased odds of having been induced post-term in their first pregnancy. The adjusted odds ratio was found to be 6.08 (95% CI 5.30-6.98).
CONCLUSIONS: Women with a first post-term pregnancy are less likely to labour spontaneously and more likely to have a second post-term pregnancy with a higher risk of repeat induction of labour, than women who have previously delivered at term. These findings could be useful in the counselling of women with a previous post-term pregnancy. Given that these women are less likely to labour spontaneously, the offer of an elective induction could also be considered to potentially improve maternal and perinatal outcomes.