THE RISK OF PRETERM BIRTH ACROSS GENERATIONS

Objective: To examine the risk of preterm birth for mothers who themse lves were born before term. Methods: Data were taken from a linked dat a base of birth certificates composed of two cohorts: 1) a parental co hort of women born between 1947 and 1957 and 2) their offspring born b etween 1970 and 1992. ''Preterm mothers'' were women in the parental c ohort who were born at less than 37 weeks' gestation. ''Term mothers'' were women in the parental cohort born at or after 38 weeks' gestatio n. Preterm mothers and term mothers were matched for birth year, count y of birth, marital status, parity, and age. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for the risk of preterm de livery in preterm mothers. Multiple logistic regression was used to as sess the interaction of concomitant variables with the risk of prematu re delivery. Results: The risk of preterm birth was significantly high er in preterm mothers than in term mothers (OR 1.18; 95% CI 1.02, 1.37 ). This risk increased as the gestational age at the `mothers' birth d ecreased (less than 30 weeks': OR 2.38; 95% CI 1.37, 4.16). The intera ction between maternal age and parity increased the risk of preterm de livery at less than 34 weeks in some age and parity strata. Conclusion : An increased risk of preterm delivery exists for women who themselve s were born before 37 weeks' gestation. This risk is inversely correla ted with the maternal gestational age at birth and is influenced by ma ternal age and parity. (C) 1997 by The American College of Obstetricia ns;and Gynecologists.