MATERNAL AGE AT 1ST CHILDBIRTH AND RISK OF LOW-BIRTH-WEIGHT AND PRETERM DELIVERY IN WASHINGTON-STATE

Objective.-To study the consequences of delayed first childbearing in a large, population-based US sample, with separate analysis of women a ged 40 years or more and adjustment for socioeconomic factors, smoking , medical and reproductive conditions, and route of delivery. Design a nd Setting.-Retrospective survey of Washington State birth certificate s from 1984 through 1988. Subjects.-First liveborn singleton infants o f women aged at least 20 years. Of eligible white infants, all those b orn to women aged 35 to 39 years (n=4019) and 40 years or more (n=410) and a maternal age-stratified random sample of white infants of young er women were studied. All eligible black infants were studied. Outcom e Measures.-Low (<2500 g) and very low (<1500 g) birth weight and pret erm delivery (<37 weeks of gestation). Results.-Adjusted odds ratios f or delivering a low-birth-weight white infant increased progressively with each 5-year maternal age group, reaching 2.3 (95% confidence inte rval, 1.6 to 3.4) for women aged 40 years or more compared with those aged 20 to 24 years. The maternal age effects for very low birth weigh t and preterm delivery were similar; for each, the odds ratio was 1.8 for the oldest group. No significant maternal age effect was found amo ng births of black infants, but only 127 births to women aged 35 years or more were studied. Conclusion.-Increasing maternal age at first ch ildbirth is an independent risk factor for low birth weight and preter m delivery of white infants in the United States.