Does the increased risk of preterm delivery in teenagers persist in pregnancies after the teenage period?

Objective To study the associations between low maternal age at first birth and the risks of very and moderately preterm birth, in first birth and in second successive birth in adulthood. Design Population-based cohort study. Setting Sweden. Population Women aged less than 25 years at first birth (n = 275,933), havi ng two successive live single births from 1973 through 1993. Methods Odds ratios with 95 percent confidence intervals were calculated to estimate the effect of low maternal age at first birth. Analyses of first births were adjusted for year of first birth and maternal education and in second births also for previous pregnancy outcomes and interpregnancy inter val. Main outcome measures Very preterm birth (less than 33 completed weeks) and moderately preterm birth (33-36 completed weeks). Results Compared with women aged 20 to 24 years at first birth, mothers age d 13 to 15 years were at increased risk of very preterm birth (odds ratio = 4.8). The corresponding risks among women aged 16 to 17 years at first bir th were doubled (odds ratio = 2.3). The influence of maternal age on risks of moderately preterm birth was similar, although the age related risks wer e lower. At second birth, risks of preterm birth were reduced in all age gr oups. However, mothers who were 17 years or less at first birth, faced, com pared with mothers aged 20-24 years, significantly larger reduction in risk s of very and moderately preterm birth. Conclusions Our results suggest that there may be a biological effect of ve ry young maternal age, affecting foremost very preterm birth.