RISK OF PRETERM DELIVERY, LOW-BIRTH-WEIGHT AND GROWTH-RETARDATION FOLLOWING SPONTANEOUS-ABORTION - A REGISTRY-BASED STUDY IN DENMARK

Background Some studies have found an association between spontaneous abortion and adverse birth outcome in the subsequent pregnancy, but re sults are conflicting maybe due to lack of confounder control. Methods Using population-based registries we identified a cohort of 45 449 wo men having a livebirth preceded by a spontaneous abortion ('abortion c ohort'), and a random sample of 9752 women with two consecutive livebi rths ('reference cohort'), We examined the risk of preterm (<37 weeks gestation) and very preterm delivery (<34 weeks), low birthweight and growth retardation in both births in the reference cohort compared wit h births following an abortion, controlling for social factors and int erpregnancy interval. Results Compared to second births in the referen ce cohort, the abortion cohort had higher risks for preterm (odds rati o [OR] = 1.74, 95% CI: 1.5-2.0) and very preterm delivery (OR = 2.17, 95% CI : 1.7-2.7), low birthweight (OR = 1.76, 95% CI: 1.5-2.1), and g rowth retardation (OR = 1.50, 95% CI: 1.4-1.6). In the reference cohor t 3.9% of the pregnancies ended as preterm deliveries, 1% as very pret erm, 3.3% as low birthweight, and 8.1% as growth retarded. Women with two or more previous abortions had a higher risk for preterm and very preterm delivery. When first liveborns of women in the reference cohor t were compared with first liveborns in the abortion cohort, only deli veries before 34 and 37 weeks' gestation were associated with previous abortion. Conclusions Spontaneous abortion is associated with preterm delivery (both <34 and <37 weeks) in the subsequent pregnancy. Women who become pregnant following an abortion should receive special atten tion in the antenatal clinics.