As expected, the proportion of premature births was greatest in the
two older age groups (11% of all births in the 35–39, and 16.6% in the
≥40 group). An increased prevalence in preterm delivery has been reported
for older women [6–18]. This increase is likely linked to the
higher frequencies of pregnancy-related complications. These complications
may produce early onset of labor or lead to the need for induction
of labor. This hypothesis is supported by the higher frequency of
induced deliveries that occurred in the women ≥40 years (31.3%) in
this population and in other study populations [7,16,17].