Interactive effects of advanced maternal age and antral follicle count on preterm birth in women undergoing ART

The association between advanced maternal age (AMA) and preterm birth (PTB) in assisted reproductive technology (ART) pregnancies remains inconsistent. We examined whether ovarian reserve, indexed by antral follicle count (AFC), modifies the association between maternal age and singleton PTB in women undergoing autologous frozen embryo transfer (FET). This prospective cohort study was conducted within the Anhui Maternal-Child Health Cohort Study in China. A total of 2,198 infertile couples who underwent ART treatment with autologous gametes were consecutively recruited between May 2017 and April 2021. Maternal age at embryo transfer was analyzed as both a categorical and a continuous variable. AFC was measured on cycle day 2-5 by transvaginal ultrasonography and categorized as ≤ 10 or > 10. Multiple adjusted odds ratios (ORs) for PTB in relation to maternal age were calculated and the interactive effects between maternal age and AFC on PTB were evaluated in logistic regression models. Among 1,035 women, 123 (11.9%) experienced singleton PTB. Maternal age alone was not independently associated with PTB after multivariable adjustment, although women aged 40–45 years had higher PTB odds than those aged 20–<30 years in the fully adjusted model (OR 3.45, 95% CI:0.85–13.98), with borderline statistical significance. A potential interaction between maternal age and AFC was observed (3.69, CI 1.03–13.21). Among women aged 35–45 years, AFC ≤ 10 was associated with increased PTB risk (3.70, 1.03–13.30). Maternal age alone was not independently associated with PTB in this autologous FET cohort. Increased PTB risk appeared to be concentrated among older women with low AFC, suggesting that ovarian reserve may modify age-related PTB risk in ART pregnancies.