A population-based study of the relationship between advanced maternal age and premature/early-term birth in Brazil.

Objective: To verify whether advanced maternal age (AMA), defined as women of ≥35 years, is associated with premature and early-term birth in Brazil, according to the onset of labor (spontaneous or provider-initiated).

Methods: Cross-sectional population-based study. The "Birth in Brazil" study interviewed 23 894 puerperal women between 2011 and 2012, in all regions of Brazil. The current analysis included 17 994 adult mothers and their newborns (15 448 aged between 20-34 years, and 2536 ≥ 35 years). A propensity score was used to assess the likelihood of AMA women giving birth to premature or early-term infants (spontaneous or provider-initiated) compared to women aged 20-34 years. To balance the groups, we used maternal, prenatal, and childbirth characteristics.

Results: The general prematurity rate was 10.24%, of which the majority of births were spontaneous (55.73%). Conversely, early-term births were more often provider-initiated (54.81%). AMA did not increase the chance of premature births, whether spontaneous or provider-initiated. However, AMA was associated with a higher rate of provider-initiated early-term birth (OR = 1.48; 95% CI: 1.23-1.77).

Conclusion: AMA alone does not contribute to premature birth; AMA's independent association with provider-initiated early-term birth may not be based solely on clinical indications.