Low maternal weight gain in the second or third trimester increases the risk for intrauterine growth retardation.

Low maternal weight gain during pregnancy has been suggested as a cause of intrauterine growth retardation (IUGR). However, pregnancy weight gain and fetal growth vary greatly throughout pregnancy. We examined the relationship between maternal weight gain in individual trimesters to the risk of IUGR in 10,696 women enrolled in the National Collaborative Perinatal Project (NCPP) and the Child Health and Development Study (CHDS). Low weight gain was defined as <-0.1 kg/wk for the first trimester and <0.3 kg/wk for the second and third trimester. IUGR was defined as a birth weight <2500 g in full-term infants. Low weight gain in the first trimester was not associated with an increased risk of IUGR. After controlling for confounding factors (maternal height, body mass index, parity, race, toxemia, diabetes), low weight gain in the second trimester was associated with a relative risk of IUGR of 1.8 (1.3-2.6) in the NCPP cohort and 2.6 (1.6-4.1) in the CHDS cohort. Similarly, low weight gain in the third trimester was associated with a relative risk of IUGR of 1.7 (1.3-2.3) in the NCPP cohort and 2.5 (1.7-3.8) in the CHDS cohort. After correcting for weight gain in other trimesters, this increased risk remained. Increased risk of IUGR was observed with low second and third trimester weight gain across the spectrum of maternal body mass index. The risk of low weight gain in the second or third trimester was significantly lower in teenagers and significantly greater in overweight women and women aged 35 y or older. Low weight gain in either the second or third trimester was associated with a significantly greater risk of intrauterine growth retardation in two distinct cohorts. We conclude that increased awareness of maternal weight gain in mid and late pregnancy is critical to identifying infants at risk for IUGR.