At what age does the risk for adverse maternal and infant outcomes increase? Nationwide register-based study on first...

It is poorly understood if there are specific ages at which adverse outcomes during pregnancy and childbirth start to increase (threshold-ages). The purpose of this study was to examine at which maternal ages the use of maternity care and the risks for adverse maternal and infant outcomes increase.

National data from the Finnish Medical Birth Register including all first-time mothers aged 20 years or over with singleton pregnancies in 2005-2014 were analyzed (n = 228 348). Odds ratios for each outcome at different ages were calculated by logistic regression, using women aged 20-24 (n = 56 282) as the reference and adjusting for socioeconomic position and urbanity of residence. The threshold-age was defined as the first significant adjusted odds ratio after which the risk remained significant.

The threshold-ages for use of maternity care varied from 25 years for cesarean section (OR 1.08, 95% CI 1.03-1.14) to 38 years for having 16 or more antenatal visits (1.13, 1.04-1.21). Four threshold-ages were found for maternal health outcomes: 25 years for gestational diabetes (OR 1.15, 1.09-1.23), 27 years for placenta previa (OR 1.75, 1.11-2.75), 33 years for gestational hypertension (1.14, 1.03-1.27), and 38 years for preeclampsia (OR 1.48, 1.12-1.96). The threshold-ages for infant health outcomes varied from 28 years for preterm birth (37 weeks, OR 1.10, 1.02-1.19) to 36 years for perinatal mortality (OR 2.10, 1.44-3.07).

Different threshold-ages were identified. Most adverse outcomes occurred earlier than the traditional cut-off ages for high risk pregnancy, which have been set at 35 or 40 years.