Risk of preterm delivery, low birthweight 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 results are conflicting, maybe due to lack of confounder control.


METHODS
Using population-based registries we identified a cohort of 45 449 women having a livebirth preceded by a spontaneous abortion ('abortion cohort'), and a random sample of 9752 women with two consecutive livebirths ('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 with births following an abortion, controlling for social factors and interpregnancy interval.


RESULTS
Compared to second births in the reference cohort, the abortion cohort had higher risks for preterm (odds ratio [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 growth retardation (OR = 1.50, 95% CI: 1.4-1.6). In the reference cohort 3.9% of the pregnancies ended as preterm deliveries, 1 % as very preterm, 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 cohort were compared with first liveborns in the abortion cohort, only deliveries 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 attention in the antenatal clinics.
The Danish Epidemiology Science Centre, Department of Epidemiology and Social Medicine, Aarhus University, Denmark.
O
O
Basso
J
J
Olsen
K
K
Christensen
D000022:Abortion, Spontaneous / Q000453:epidemiology*; D000328:Adult; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005317:Fetal Growth Retardation / Q000453:epidemiology*; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007752:Obstetric Labor, Premature / Q000453:epidemiology*; D011247:Pregnancy; D011256:Pregnancy Outcome; D012042:Registries; D012307:Risk Factors; D013997:Time Factors