Maternal age and pregnancy outcomes in twin compared with singleton gestations.

Objective: To estimate the association of advanced maternal age with pregnancy complications in twin pregnancies and compare it with that observed in singleton pregnancies.

Methods: A population-based retrospective cohort study of all patients with a singleton or twin hospital birth in Ontario, Canada, between 2012 and 2019. The primary outcome was preterm birth (PTB) less than 34 weeks. Pregnancy outcomes were stratified by maternal age groups in twin pregnancies and, separately, in singleton pregnancies.

Results: A total of 935 378 patients met the study criteria: 920503 (98.4%) had a singleton pregnancy and 14 875 (1.6%) had twins. In singletons, the rate of PTB less than 34 weeks increased progressively with increasing maternal age and was highest for patients aged 45 years or more (3.4%; adjusted risk ratio [aRR] 1.56, 95% confidence interval [CI] 1.05-2.33). By contrast, in twins, although the rate of PTB less than 34 was highest patients under 20 years of age (25.3%) and was lowest among patients aged 35-39 years (11.7%), the associations between maternal age group and the risk of PTB were not statistically significant in the adjusted analysis.

Conclusion: Although the absolute rates of pregnancy complications are higher in twin pregnancies, there are considerable differences in the relationship between maternal age and the risk of certain complications between twin and singleton pregnancies.