Recent trends in fetal and infant outcomes following post-term pregnancies

All births and infant deaths in 1985-87 and 1992-94 in Canada, except in Ontario and Newfoundland, were analyzed to assess the potential impact of the recent increased use of elective labour induction for post-term pregnancies. Probabilistic linkage was carried out of infant death records (Canadian Mortality Database) and respective birth registrations (Canadian Birth Database)for the periods 1985-87 and 1992-94. The combined fetal and infant mortality declined by 20-30% between 1985-87 and 1992-94 at each gestational week beginning at 37 weeks, with no increased reduction among post-term pregnancies. Asphyxia-related fetal and infant deaths, the most likely cause of death being preventable by labour induction for post-term pregnancies, did not decrease among post-term pregnancies. On the contrary, a substantial decrease of asphyxia-related deaths was observed at 37 and 38 weeks over the same periods of time. Because fetal and infant deaths are rare events and because the number of pregnancies passing 42 weeks of gestation decreased dramatically during 1992-94, statistically unstable results may be inevitable in the comparison of mortality in this group of pregnancies.