Age-specific effects on adverse pregnancy outcomes vary by maternal characteristics: a population-based retrospective study in Xiamen, China

Background Advanced maternal age (AMA; ≥35 years) is considered to be a major risk factor for adverse pregnancy outcomes. Along with the global trend of delayed childbearing, and in particular, the implementation of China’s second and third-child policy leading to a dramatic increase of AMA in recent years, the association between maternal age and pregnancy outcomes requires more investigation. Methods A population-based retrospective study was performed. Data were derived from the Medical Birth Registry of Xiamen from 2011 to 2018. Univariate and multivariate logistic regression was used to evaluate the effects of maternal age on pregnancy outcomes. Results A total of 63,137 women categorized into different age groups (< 25 years, 25–29 years, 30–34 years, and ≥ 35 years) were included in this study. Compared with the mothers aged 25–29 years, the univariate regression analysis showed that mothers aged < 25 years had lower risks of gestational diabetes mellitus (GDM) and cesarean. AMA was associated with higher risks of GDM, hypertension, cesarean, preterm birth, low-birth weight (LBW), large-for-gestational-age (LGA), macrosomia, and stillbirth (all P < 0.01). After adjustment for potential confounding factors, increased risks of GDM, hypertension, cesarean, preterm birth, and LBW remained significantly associated with AMA (all P < 0.05), whereas AMA mothers showed a lower risk of macrosomia than their younger counterparts. Additionally, no significant differences were detected in terms of Apgar score < 7. Conclusion AMA was associated with adverse pregnancy outcomes including increased risks of GDM, hypertension, cesarean, preterm birth, and LBW. This study confirmed the relationship between AMA and certain adverse maternal and fetal outcomes and emphasizes the necessity for women to be cautious about the age at which they become pregnant.