as age and race/ethnicity; physiological factors, some of which are also discussed in depth elsewhere in this report, and genetic factors known to impact GWG and those that may impact GWG because of their known influence on birth weight; and developmental and epigenetic programming in the mother, which may influence how a woman responds later in life.

Sociodemographic Factors

Gestational Weight Gain in Adolescents

Adolescent pregnancy has been associated with increased risk of preterm delivery, low birth weight, SGA births, and increased risk of neonatal mortality, although reported risk associations vary (Chen et al., 2007). To reduce these risks, the IOM (1990) report recommended that pregnant adolescents gain weight within the ranges for adult women unless they were under 16 years of age or less than 2 years post-menarche. In either of these cases, adolescents were encouraged to gain at the upper limits of the GWG guidelines for their prepregnancy BMI category.

The youngest adolescents as well as somewhat older adolescents who conceive soon after menarche may still be growing themselves (Scholl and Hediger, 1993). Even girls who become pregnant for a second time during adolescence may still be growing. Scholl et al. (1990) showed that adolescents who were still growing during a first pregnancy delivered infants whose birth weight did not differ from those who were not growing. This was not true among adolescents who were still growing during a second pregnancy; their infants were significantly lighter at birth than those who were not growing themselves. The possibility of a competition for nutrients between the still-growing adolescent gravida and her fetus has been advanced as an argument for recommending relatively higher gains for at least some pregnant adolescents. What has been found instead is that still-growing adolescents are not mobilizing their fat gain during pregnancy to enhance fetal growth but, rather, are supporting the continued development of their own fat stores (Scholl et al., 1994).

In a retrospective review of natality data from 2000, Howie et al. (2003) reported an increased likelihood for excessive GWG among adolescents compared to older women. Other authors have corroborated that younger adolescents have a higher GWG compared to older adolescents and adults, but whether the infant benefits from this greater weight gain is not yet clear (Hediger et al., 1990; Scholl et al., 1990; Stevens-Simon et al., 1993a). This is in part because—as is also the case for adult women—increases in GWG not only reduce the risk of delivering a low birth weight infant but also increase the risk of delivering a macrosomic infant (Scholl

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