Interpregnancy interval and low birth weight: findings from a case-control study.

In a case-control study in Natal, northeast Brazil, conducted between September 1984 and February 1986, 303 cases of intrauterine growth retardation and 282 cases of preterm delivery were compared with 1,710 normal controls to ascertain the effects of the preceding birth-to-conception interval on pregnancy outcome. The risk of intrauterine growth retardation associated with interpregnancy intervals of six months or less was 1.38 (95% confidence interval (CI): 1.02-1.86) after adjustment for maternal age, education, smoking, and prior fetal loss or low birth weight. When maternal postpartum body weight was introduced into the logistic model, the risk of intrauterine growth retardation decreased slightly to 1.25 and was no longer significant (95% CI: 0.91-1.72). Short interpregnancy intervals (six months or less) were more frequently observed in women with postpartum body weight of less than 45 kg (31.1%) than in women weighing 50 kg or more (18.9%), which might suggest that the effect of short intervals on the risk of intrauterine growth retardation is mediated through maternal nutritional status. No association was found between birth-to-conception intervals and preterm delivery.