It is axiomatic that small women typically have smaller newborns. As discussed subsequently, both prepregnancy weight and gestational weight gain modulate this risk. Durie and colleagues (2011) showed that the risk of delivering an SGA neonate was highest among underweight women who gained less weight than recommended by the Institute of Medicine (Chap. 9, p. 166). Also, both maternal and paternal size inluences birthweight. In a Swedish study of 137,538 term births, it was estimated that the maternal and paternal birthweights explained 6 and 3 percent of variance in birthweight, respectively (Mattsson, 2013).
In the study by Durie (2011) cited above, gestational weight gain during the second and third trimesters that was less than
FIGURE 44-4 Risk factors and causes of impaired fetal growth centering on the mother, her fetus, and the placenta.
that recommended by the Institute of Medicine was associated with SGA neonates in women of all weight categories except class II or III obesity. Conversely, excessive gestational weight gain was associated with an overgrown newborn in all weight categories (Blackwell, 2016).
As perhaps expected, eating disorders are linked with significantly higher risks for low birthweight and preterm birth (Micali, 2016). Marked weight gain restriction ater midpregnancy should not be encouraged even in obese women (Chap. 48, p. 941). Even so, it appears that food restriction to < 1500 kcal/d adversely afects fetal growth minimally (Lechtig, 1975). The best documented efect of famine on fetal growth was in the Hunger Winter of 1944 in Holland. For 6 months, the German occupation army restricted dietary intake to 500 kcal/ d for civilians, including pregnant women. This resulted in an average birthweight decline of only 250 g (Stein, 1975).
It is unclear whether undernourished women may beneit from micronutrient supplementation. In one study, almost 32,000 Indonesian women were randomly assigned to receive micronutrient supplementation or only iron and folate tablets (Prado, 2012). Ofspring of those receiving the supplement had lower risks of early infant mortality and low birthweight and had improved childhood motor and cognitive abilities. Conversely, Liu and coworkers (2013) randomly assigned 18,775 nulliparas to folic acid alone; folic acid and iron; or folic acid, iron, and 13 other micronutrients. Folic acid and iron, with or without the additional micro nutrients, resulted in a 30-percent reduction in risk of third-trimester anemia. But, supplementation did not afect other maternal or neonatal outcomes. A Cochrane database review of 19 trials involving 138,538 women concluded that supplementation of iron and folic acid improved birth outcomes, including lower risks of low birthweight and SGA (Haider, 2017). he importance of antenatal vitamins and trace metals is further discussed in Chapter 9 (p. 168).
Exercise in pregnancy may be beneficial for optimal fetal growth. One metaanalysis of28 studies involving 5322 women concluded that exercise reduces the risk of fetal overgrowth without raising the risk of poor growth (Wiebe, 2015). Another metaanalysis concluded that aerobic exercise did not result in low-birthweight neonates (Di Mascio, 2016).
The efect of social deprivation on birthweight is interconnected with lifestyle factors such as smoking, alcohol or other substance abuse, and poor nutrition. With appropriate modiying interventions, women with psychosocial factors were signiicantly less likely to deliver a low-birthweight infant and also had fewer preterm births and other pregnancy complications (Coker, 2012).