Combined effects of increasing maternal age and nulliparity on hypertensive disorders of pregnancy and small for gestational age

Background: The mean age of women delivering for the first time is increasing, and this combination could lead to an increased risk of perinatal complications. Objectives: The objective was to evaluate the potential combined effects of nulliparity and increasing maternal age on small for gestational age (SGA < 10th percentile) and hypertensive disorders of pregnancy (HDP). Study design: A population-based cohort study was conducted using data routinely collected on all births in 11 hospitals in the Burgundy perinatal network between 2007 and 2016. Pregnant women with singleton deliveries aged 20 years or older were included at delivery and divided into groups according to maternal age (20 to 24-year-old group as a reference). Multivariate logistic regression models, adjusted on smoking, body mass index, chronic high blood pressure and birth date, were performed. Results: A total of 137,791 women were included. Whatever the parity, the risks of SGA and HDP increased with maternal age, but the increase began earlier in nulliparous women. Compared to multiparous women, the risk of SGA in nulliparous women increased with maternal age (aOR = 1.5 95% CI [1.4-1.7] for age 20-24 rising to 2.2 [1.8-2.8] for age 40-49). We found evidence that parity modified the association between maternal age and SGA (test for interaction p < 0.001). The risk of HDP was constantly higher in nulliparous women, whatever the maternal age. Conclusion: The combination of increasing maternal age and nulliparity has a more negative impact on the occurrence of SGA than either risk factor alone.