Preterm birth, stillbirth and infant mortality among triplet births in Canada, 1985-96.

Recent increases in the frequency of multiple births and simultaneous increases in preterm birth among multiple births have focused attention on such births. However, most previous studies have examined twins rather than higher-order multiples. We carried out a study to examine rates and trends in preterm birth and in gestational age-specific fetal and infant mortality among triplet births in Canada. We used data from the stillbirth, live birth and mortality files of Statistics Canada for the years 1985-97. All births in Canada (excluding those occurring in Ontario and Newfoundland) were included in the study, with two periods (1985-90 vs. 1991-96) being contrasted for assessing temporal change. Changes were estimated using relative risks, 95 confidence intervals [CI] and two-tailed P-values. The rate of preterm birth among triplet live births increased by 6 (95 CI 3, 9) from 90.4 in 1985-90 to 96.0 in 1991-96. Stillbirth rates among triplets did not change significantly and were 30.3 per 1000 total births in 1985-90 and 33.8 per 1000 total births in 1991-96. Infant mortality among triplets declined from 112.7 per 1000 live births in 1985-90 to 73.8 per 1000 live births in 1991-96. In spite of temporal reductions in infant mortality, triplet births continue to be associated with very high rates of preterm birth and fetal and infant mortality. Fetal mortality among triplets has not changed over the last ten years.