To examine whether the recent substantial increase in preterm birth among twins has been associated with changes in fetal and infant mortality.
Cohort study based on information in the linked live birth, stillbirth, and mortality databases of Statistics Canada.
Ten of 12 provinces and territories in Canada.
All twin live births and stillbirths between 1985 and 1996, along with information on deaths during infancy (1985-1997).
Fetal and infant mortality rates.
The rate of preterm birth among twin live births increased significantly by 17% (95% confidence interval: 14%-20%) from 42.5% between 1985 and 1987 to 49.6% between 1994 and 1996. Overall, stillbirth rates among twins declined from 22.4 per 1000 total births in 1985 to 1987 to 18.8 per 1000 total births in 1994 to 1996. Among twin fetuses >/=34 weeks' gestation, stillbirth rates decreased from 9.5 per 1000 in 1985 to 1987 to 5.4 per 1000 fetuses at risk in 1994 to 1996. Infant mortality rates among twin live births declined substantially in all categories of gestational age above 24 weeks except for live births at 32 to 33 and 34 to 36 weeks' gestation.
The recent increase in preterm birth among twins was associated with a substantial reduction in stillbirth rates at and near term gestation. Infant mortality rates declined concurrently, although the absence of a significant decrease in infant mortality among twin live births at 32 to 33 and 34 to 36 weeks' gestational age needs additional scrutiny.
The World Health Organization defines preterm birth as birth at less than 37 completed gestational weeks, but most studies have focused on very preterm infants (birth at /=37 gestational weeks).
Relative risks for infant death from all causes among singletons born at 32 through 33 gestational weeks were 6.6 (95% confidence interval [CI], 6.1-7.0) in the United States in 1995 and 15.2 (95% CI, 13.2-17.5) in Canada in 1992-1994; among singletons born at 34 through 36 gestational weeks, the RRs were 2.9 (95% CI, 2.8-3.0) and 4.5 (95% CI, 4.0-5.0), respectively. Corresponding EFs were 3.2% and 4.8%, respectively, at 32 through 33 gestational weeks and 6.3% and 8.0%, respectively, at 34 through 36 gestational weeks; the sum of the EFs for births at 32 through 33 and 34 through 36 gestational weeks exceeded those for births at 28 through 31 gestational weeks. Substantial RRs were observed overall for the neonatal (eg, for early neonatal deaths, 14.6 and 33.0 for US and Canadian infants, respectively, born at 32-33 gestational weeks; EFs, 3.6% and and 6. 2% for US and Canadian infants, respectively) and postneonatal (RRs, 2.1-3.8 and 3.0-7.0 for US and Canadian infants, respectively, born at 32-36 gestational weeks; EFs, 2.7%-5.8% and 3.0%-7.0% for the same groups, respectively) periods and for death due to asphyxia, infection, sudden infant death syndrome, and external causes. Except for a reduction in the RR and EF for neonatal mortality due to infection, the patterns have changed little since 1985 in either country.
Mild- and moderate-preterm birth infants are at high RR for death during infancy and are responsible for an important fraction of infant deaths. JAMA. 2000;284:843-849
We studied infant mortality rates in Canada within specific gestational age and birthweight categories after using probabilistic techniques to link information in Statistics Canada's live births data base (1985-94) with that in the death data base (1985-95). Gestational age- and birthweight-specific mortality rates in 1992-94 were contrasted with those in 1985-87 with changes expressed in terms of relative risks with 95% confidence intervals [CI]. Statistically significant reductions in infant mortality were observed beginning at 24-25 weeks of gestation and extended across the gestational age range to post-term births. Crude infant mortality rates, infant mortality rates among those > or = 500 g and among those > or = 1000 g decreased by 22%, 25% and 26%, respectively, from 1985-87 to 1992-94. The magnitude of the reductions in infant mortality rates ranged from 14% [95% CI 7, 21%] at 24-25 weeks of gestation to 40% [95% CI 31, 47%] at 28-31 weeks. Almost all reductions in gestational age- and birthweight-specific infant mortality between 1985-87 and 1992-94 were due to approximately equal reductions in neonatal and post-neonatal mortality. Live births > or = 42 weeks of gestation did not follow this rule; post-neonatal mortality rates among such live births decreased significantly by 51% [95% CI 26, 68%], although neonatal mortality rates showed no significant change. The mortality reductions observed across the gestational age and birthweight range are probably a consequence of specific clinical interventions complementing improvements in fetal growth. Temporal changes in the outcome of post-term pregnancies need to be carefully examined, especially in relation to recent changes in the obstetric management of such 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. In 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.
To identify spatial patterns of changes in infant mortality rates and proportions of low-birth-weight live births observed in 1994.
Live births and infant deaths in Canada between 1987 and 1994. Data for Newfoundland were unavailable for 1987 through 1990.
Annual infant mortality rates (crude and after excluding live newborns weighing less than 500 g); proportion of live births by low-birth-weight category (500-2499 g).
Nova Scotia, New Brunswick, Quebec and Manitoba had lower crude and adjusted infant mortality rates in 1994 than in 1993. Newfoundland, Saskatchewan, Alberta and British Columbia had higher rates in 1994 than in 1993. The crude rate in Ontario was lower, and the adjusted rate higher, in 1994 than in 1993. A downward trend in the proportion of low-birth-weight live births was observed in Quebec (chi(2) for trend = 29.2, p
Cites: Int J Epidemiol. 1995 Jun;24(3):583-87672900
Cites: Lancet. 1995 Aug 19;346(8973):486-87637485
Cites: Am J Epidemiol. 1976 Feb;103(2):226-351251836
Cites: CMAJ. 1996 Oct 15;155(8):1047-528873632
Cites: CMAJ. 1997 Jan 15;156(2):161-39012715
Comment In: CMAJ. 1997 Sep 15;157(6):646-79307550
Comment In: CMAJ. 1997 Dec 15;157(12):1737-99418677
Prenatal diagnosis of major congenital anomalies and subsequent termination of affected pregnancies has been widely available as part of routine obstetric care in recent years. In this study, vital statistical data on stillbirths, live births, and infant deaths were used to examine secular trends in gestational age-specific and category-specific fetal and infant mortality due to congenital anomalies in Canada (excluding Ontario and Newfoundland) from 1985-1996. Comparisons of the rates between 1985-1987 and 1994-1996 were made using relative risks and 95% confidence intervals (CI). The overall fetal mortality rate due to congenital anomalies increased significantly, from 68.0 per 100,000 total births in 1985-1987 to 78.6 per 100,000 total births in 1994-1996, while the overall infant mortality rate due to congenital anomalies decreased significantly over the same period, from 2.47 to 1.79 per 1,000 live births. The fetal death rate due to congenital anomalies at 20-21 weeks of gestation increased approximately five-fold (relative risk [RR] = 4.83, 95% CI = 3.28-7.11) from 4.5 to 21.5 per 100,000 fetuses at risk, while the rate at 37-41 weeks decreased by 30% (RR = 0.70, 95% CI = 0.50-0.97). Fetal death rates among pregnancies at 20-25 weeks of gestation increased in all categories of congenital anomaly except anencephaly and respiratory system anomalies. Congenital anomaly-related fetal and infant deaths have increased at early gestation but declined at later gestation in Canada. These changes suggest an increase in prenatal diagnosis and selective termination of pregnancies with congenital anomalies in recent years.