activity level (PAL) and BMI on GWG in 223 healthy Swedish women. Pregravid PAL was related to decreased weight gain in the third trimester, about 0.10 kg/week less in the high-PAL than in the low- or medium-PAL groups. Maternal BMI was inversely associated with weight gain in the second trimester but there was a positive association between maternal BMI and GWG in the third trimester. However, maternal smoking, parity, education, age, and pregravid PAL explained only 4 percent of the variance in maternal weight gain, and PAL was not related to birth weight.

In sum, several studies have demonstrated an inverse relationship between the level of physical activity and GWG. Based on energetic fundamentals alone, maintaining a reasonable level of exercise-related energy expenditure during pregnancy should moderate GWG. Energy requirements based on PAL are provided in Appendix B.

Substance Abuse

Cigarette smoking Taken together, early studies examining associations between decreasing GWG and amount of reported smoking show inconclusive results. Rush (1974) found a strong relationship between amount of smoking and decreasing GWG (p < 0.01), while Garn et al. (1979) found no association between smoking and nonsmoking mothers and GWG. Several investigators examined whether smoking had a negative effect on caloric intake as a causative factor for higher incidence of SGA in smoking mothers. Haworth et al. (1980) found that women who smoked during pregnancy actually had higher mean caloric intakes with no difference in GWG; but a greater number of low birth weight infants than nonsmokers. Similarly, Papoz et al. (1982) found higher mean caloric intake and lower birth weight in women who smoked during pregnancy. More recently, Furuno et al. (2004) found no significant difference in mean GWG between smoking and nonsmoking mothers but did find a slightly increased (1.3-fold) risk for low GWG among smokers.

Although there is limited evidence that cigarette smoking may be inversely associated with GWG there is a preponderance of evidence that supports an independent effect of smoking on birth weight (Muscati et al., 1988; Wolff et al., 1993; Adriananse et al., 1996). Secker-Walker and Vacek (2003) examined the effect of smoking on birth weight independent of GWG and found that gains in infant birth weight among mothers who stopped smoking during pregnancy were not related to GWG, but rather to the independent effect of smoking on birth weight.

Alcohol use Little information is available about effects of alcohol consumption on GWG. Wells et al. (2006) assessed biological, psychological,

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