Background Serious adverse pregnancy outcomes (such as congenital anomalies and fetal or infant deaths) are more likely in a woman’s second pregnancy if she experienced an adverse event in her first. This may partly be due to repeated risk factors such as maternal pre-existing (type 1 or type 2) diabetes, which is associated with a high risk of pregnancy complication. It is not known, however, whether women with diabetes experience the same pattern of recurrence as the general population, or how the risk divides between the first and subsequent pregnancy. This study sought to address these uncertainties using data from the UKs longest-running survey of women with pre-existing diabetes.

Methods The study examined 442 pregnancies occurring in 221 women with pre-existing diabetes who delivered successive singleton pregnancies in the North of England during 1996–2008. The sample was obtained from the population-based Northern Diabetes in Pregnancy Survey (NorDIP), which collects information on a range of maternal clinical and socio-demographic factors. Predictors of serious adverse pregnancy outcome were estimated by competing-risks regression. Peri-conception glycated haemoglobin concentration (HbA_1c) – an estimate of blood glucose concentration – was analysed by piecewise regression due to evidence of non-linearity.

Results 68 (31%) first pregnancies ended in serious adverse outcome, including 14 (6%) with congenital anomalies and 54 (24%) additional fetal or infant deaths. 41 (19%) second pregnancies ended in serious adverse outcome – 44% lower than the rate among first pregnancies (p = 0.0008), including 21 (10%) with congenital anomalies and 17 (9%) additional fetal or infant deaths. The crude probability of serious adverse outcome in the second pregnancy was over twice as high (subhazard ratio, SHR=2.69, 95% CI 1.42–5.11, p = 0.002) in women who experienced one in the first, however this was largely explained by repeated risk factors, in particular peri-conception HbA_1c (adjusted SHR, above 47mmol/mol=1.04, 95% CI 1.02–1.07, p < 0.0001). After conditioning for available explanatory variables, there was limited evidence of an additional unexplained risk of recurrence (adjusted SHR=1.40, 95% CI 0.58–3.36, p = 0.46).

Conclusion For women with pre-existing diabetes, the risk of serious adverse outcome is substantially lower in a second pregnancy than a first. History of adverse outcome is associated with an increased risk in the second pregnancy, but this is largely explained by repeated risk factors, most notably peri-conception HbA_1c. Women with diabetes who experience an adverse pregnancy outcome should be offered intensive support, beginning in the immediate postnatal period, to improve their glycaemic control before trying for their next pregnancy.