Maternal underweight in pregnancy is associated with increased risk for infants with low birthweights, miscarriage, and other complications, including anemia, antepartum hemorrhage, birth defects, intrauterine growth restriction, and premature rupture of the membranes. (Cox and Carney, 2017) Although the risks are significant, underweight is less likely to be identified as a risk factor than overweight. Important roles for dietitians include identifying women who are at-risk, and helping to assure positive birth outcomes.

Factors Associated with Low Prenatal Weight Gain (Hickey et al, 1997; Wells et al, 2006; Hickey, 2000; Deputy et al, 2015)

• Underweight (pre-pregnancy BMI <19.8)
• Obesity (pre-pregnancy BMI >29)
• Pregnancy-related nausea
• Preterm labor
• Smoking and alcohol use
• Unwanted pregnancy
• Caring for more than one preschool-aged child at home
• Not using own car for errands
• Working more than 40 hours per week

Unless there is an underlying medical cause for underweight, no medical management is generally indicated.