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Secular trends in preterm birth: a hospital-based cohort study
1Department of Epidemiology and Biostatistics, McGill University Faculty of Medicine and the Royal Victoria Hospital, Montreal, Quebec, Canada. mikek@epid.lan.mcgill.ca
JAMA
|December 10, 1998
Summary
Preterm birth rates increased due to changes in ultrasound dating, obstetric interventions, and sociodemographic factors. These trends parallel national increases, highlighting complex contributing elements to preterm birth incidence.
Area of Science:
- Obstetrics and Gynecology
- Perinatal Epidemiology
- Public Health
Background:
- Recent increases in preterm birth incidence observed in Canada and the United States.
- The underlying causes for the rise in preterm births remain largely unknown.
Purpose of the Study:
- To investigate secular trends in preterm birth rates.
- To identify potential determinants contributing to the observed increase in preterm births.
Main Methods:
- Hospital-based cohort study conducted from 1978 to 1996.
- Analysis of 65,574 nonreferred live births and stillbirths.
- Adjustment for gestational age assessment methods, obstetric interventions, birth weight registration, and sociodemographic, behavioral, and clinical factors.
Main Results:
- Secular increase in preterm births (<37, <34, <32 weeks gestation) observed across multiple estimation methods.
- Rates increased from 6.6% to 9.8% for births <37 weeks gestation.
- Trends for births <34 and <32 weeks were eliminated after excluding specific births and interventions; trend for <37 weeks attenuated by ultrasound dating, sociodemographic, and behavioral factors.
Conclusions:
- The hospital's preterm birth increase mirrors national trends in the US and Canada.
- Key contributors include increased use of early ultrasound dating, preterm induction/cesarean delivery without labor, and shifts in sociodemographic and behavioral factors.
- These factors appear to have counteracted potential reductions in preterm birth since the mid-1980s.