Objective: To investigate whether the age-related risk of adverse pregnancy outcomes in the first birth persisted in the second birth, before and after adjusting for the influence of an adverse pregnancy outcome in the first birth and for other possible confounders.
Methods: Prospectively collected longitudinal data from the Swedish Medical Birth Registry (n = 210,735 women) were analyzed to contrast the effects of maternal age at the first birth on the risk of adverse pregnancy outcomes in the first and second successive births.
Results: Rates of adverse pregnancy outcomes were substantially higher in first than in second births. Compared with women aged 20-24, women aged 30-34 years had significantly higher odds ratios (ORs) of late fetal death (OR 1.4) and early neonatal death (OR 1.4) for the first but not for second births; women aged 35+ had a significantly higher OR of late fetal death (OR 2.2) for the first but not for second births. Women over 35 also had a significantly higher OR of early neonatal death for the first birth (OR 2.8) and less of an increase for second births (OR 1.8), a higher OR of low birth weight (LBW) for the first (OR 1.5) and second births (OR 1.6), and a higher OR of preterm birth for the first (OR 1.4) and second births (OR 1.7). Despite the strong tendency to repeat an adverse pregnancy outcome in second births, the age-related ORs did not change with adjustment for the previous pregnancy outcome.
Conclusion: Women aged 30+ at their first births have increased risks of adverse pregnancy outcomes in first births. However, second births showed no age-related increase in late fetal death and a smaller increase in early neonatal death. Increased risks for LBW and preterm birth were similar for first and second births of delayed childbearers.