The authoring committee of the IOM (1990) report did not identify any studies on the association between GWG and birth defects. Since the etiologic period for congenital defects is so early in pregnancy, GWG is not likely to be causally relevant. Although the literature on prepregnancy BMI and congenital defects now suggests an increased risk of birth defects with increasing BMI (Watkins et al., 2003; Anderson et al., 2005; Villamor et al., 2008), only one study has directly addressed GWG in relation to birth defects. Shaw (2001) reported that infants born to mothers who gained less than either 5 or 10 kg during pregnancy were at increased risk of neural tube defects. An additional report indicated that dieting to lose weight during pregnancy was associated with an increased risk of neural tube defects (Carmichael et al., 2003). It seems more likely that an association of GWG and birth defects would result from reverse causality (abnormal fetal development affecting weight gain) rather than a direct causal effect of GWG on risk of birth defects.
Infant mortality is obviously of great clinical and public health importance and is often used as a summary indicator of a population’s reproductive health status. In fact, concern with fetal growth and preterm birth as health outcomes stems largely from the known relationships between those outcomes and infant mortality (as well as morbidity); studies that directly address mortality can be helpful in interpreting the patterns seen with those other, intermediate outcomes such as preterm birth or growth restriction. However, very limited research assessing GWG and infant mortality exists. In the IOM (1990) report, only one study on perinatal mortality was examined (NCHS, 1986). Since then, there has been only one additional study. As part of the National Maternal and Infant Health Survey (NMIHS), Chen et al. (2009) examined maternal prepregnancy BMI and GWG among 4,265 infant deaths and 7,293 controls. Among underweight and normal-weight women, low GWG was associated with a marked increase in infant mortality, with relative risks on the order of 3-4 compared to those with the highest GWG; the effects were more modest among overweight and obese women, with both lower and higher GWG associated with about two-fold increases in the risk of infant mortality. In all cases, the patterns were stronger for neonatal deaths (in the first 30 days of life) than for post-neonatal deaths (those occurring after 1 month but before the completion of 1 year). In the lowest weight gain group, the relative risks for neonatal death were 3.6 among underweight women, 3.1 among normal weight women, 2.0 among overweight women, and 1.2 among obese women,