RISK FOR SPONTANEOUS PRETERM DELIVERY BY COMBINED BODY-MASS INDEX ANDGESTATIONAL WEIGHT-GAIN PATTERNS

Background To investigate whether maternal anthropometric factors inte ract with one another or with other risk factors, thus modifying the r isk of spontaneous preterm delivery. Methods. We carried out a case-co ntrol study of 230 spontaneous preterm births with intact membranes be tween 24 and 35 weeks gestation and 460 control term births. All the p atients had prenatal care at the same institution. Logistic regression analysis was used to test for possible interactions adjusting for pot ential confounders. Results. A pre-pregnancy body mass index less than or equal to 19.5 Kg/m(2) (odds ratio (OR)=1.68, 95% confidence interv al (CI)=1.20-2.38) and a rate of weight gain less than or equal to 0.3 7 Kg/week during the second and third trimesters (OR=2.4, 95% CI=1.69- 3.32) were associated with an increased risk of spontaneous preterm de livery. The risk of spontaneous preterm delivery associated with a low second/third trimester weight gain was greater among patients with a body mass index less than or equal to 19.5 (OR=5.63, 95% CI=2.35-13.8) compared to those with a body mass index >19.5 (OR=2.45, 95% CI=1.60- 3.75, adjusted p value for interaction=0.05). The risk of spontaneous premature delivery associated with a maternal pre-pregnancy weight les s than or equal to 48 Kg was higher among smokers (OR=5.81, 95% CI=1.6 0-22.9) than among non-smokers (OR=2.4, 95% CI=1.53-3.74: adjusted p v alue for interaction=0.05). Conclusions. The risk of spontaneous prete rm delivery associated with a low pre-pregnancy body mass index is gre ater among patients with low rate of gestational weight gain during th e second and third trimesters compared to those with a higher rate. Th e results of this study support the recommendation for increased rates of weight gain to patients with low body mass index compared to those with a higher body mass index.