Temporal trends of preterm birth subtypes and neonatal outcomes.

OBJECTIVE: To describe temporal trends of preterm birth subtypes, neonatal morbidity, and hospital neonatal mortality.
METHODS: A database of 1.7 million births that occurred in 51 maternity hospitals in Latin America from 1985 to 2003 was studied. Subgroups of preterm births were classified according to the presence or absence of maternal medical or obstetric complications, spontaneous labor, preterm labor after premature rupture of membranes, induction of labor, or elective cesarean. Outcomes studied, for different periods, were prevalence of small for gestational age, neonatal morbidity, and neonatal mortality.
RESULTS: Spontaneous preterm labor without maternal complications was the most frequent subtype of preterm birth (60%), followed by premature rupture of membranes without maternal complications. Preterm births due to elective induction and delivery by elective cesarean increased markedly in the last 20 years, from 10% in 1985-1990 to 18.5% in recent years. Neonates born after spontaneous labor without maternal complications had the lowest mortality rate, but their large numbers made them responsible for one half of the preterm mortality. The induction followed by elective cesarean subgroups accounted for 13.4% of the preterm deaths between 1985 and 1990 and increased to 21.2% between 1996 and 2003.
CONCLUSION: Spontaneous labor in mothers without maternal complications is the most frequent cause of preterm births and is also the most important subgroup related to neonatal mortality. However, preterm births due to induction of labor or elective cesarean are increasing in Latin America and are becoming important contributors to neonatal mortality.