Clinical Question

Does antenatal dietary education or supplementation to increase energy and protein intake in pregnancy impact maternal and infant health outcomes?

Evidence-Based Answer

Antenatal dietary education appears to decrease the rate of preterm birth and increase infant birth weight among undernourished women. Providing balanced energy and protein supplements to pregnant women decreases the risk of stillbirth, low birth weight, and having an infant that is small for gestational age (number needed to treat [NNT] = 28). The use of high-protein supplements does not improve any outcomes and may cause fetal harm. Neither dietary advice nor supplementation affects maternal outcomes. (Strength of Recommendation: B, based on inconsistent or limited-quality patient-oriented evidence.)

Practice Pointers

As of 2010, the infant mortality rate in the United States ranked number 26 out of 29 developed nations surveyed.¹ Preterm births and low birth weight are important factors that influence infant mortality. In the United States, 11% of births are preterm (i.e., born before 37 weeks of gestation) and 8% of infants are born at a low birth weight (i.e., less than 2,500 g [5 lb, 8 oz]).² Reducing the incidence of low birth weight and preterm births is a stated objective of Healthy People 2020.³ The authors of this Cochrane review hoped to determine whether providing nutritional counseling to pregnant women can improve these outcomes.

This Cochrane review includes 17 randomized controlled trials with a total of 9,030 pregnant women. The variables studied were advice to increase caloric intake, advice to increase protein intake, or being given dietary supplements. There were four categories of trials: (1) trials that provided specific nutritional advice to increase dietary energy and protein intake, (2) trials that provided balanced energy and protein supplements (i.e., less than 25% of total calories from protein), (3) trials that provided high-protein supplements (i.e., more than 25% of total calories from protein), and (4) trials that provided isocaloric protein supplements. Seven of the included trials were conducted in high-income countries such as the United States and the United Kingdom, although more than two-thirds of the included women were considered undernourished or nutritionally at risk. Several studies had unclear or high risk of bias. The quality of the studies was rated low to moderate.

Antenatal dietary education affected undernourished women more than any other group. Undernourished women are those with a body mass index of less than 18 kg per m², with stunted height, or with micro- and macronutrient deficiencies. In this group, birth weight was significantly increased (mean difference [MD] = 489.76 g; 95% confidence interval [CI], 427.93 to 551.59), whereas rates of preterm birth (relative risk [RR] = 0.46; 95% CI, 0.21 to 0.98; P < .05) and low birth weight were decreased. However, these improvements did not translate into positive effects on neonatal death (defined as death in the first 28 days after birth), stillbirth, or being small for gestational age; these indices remained unchanged.

Providing balanced energy and protein supplements decreased the risk of stillbirth (RR = 0.60; 95% CI, 0.39 to 0.94) and being small for gestational age (RR = 0.79; 95% CI, 0.69 to 0.90; NNT = 28; 95% CI, 19 to 59), and increased birth weight (MD = 40.96 g; 95% CI, 4.66 to 77.26). These trials did not demonstrate any change in the rates of preterm birth or neonatal death. High-protein supplements had no effect on birth weight or preterm birth, but they nonsignificantly increased the rates of stillbirth and neonatal death. High-protein supplements also increased the number of infants who were small for gestational age (RR = 1.58; 95% CI, 1.03 to 2.41; number needed to harm = 15; 95% CI, 6 to 250). Use of isocaloric protein supplements demonstrated no benefit or harm to the women or their babies.

Current guidelines recommend that clinicians counsel pregnant women on nutrition and weight at every visit from preconception through postpartum, although specific caloric and protein recommendations are lacking.⁴ Evidence-based reviews recommend increasing daily energy intake by 300 to 400 calories in the second and third trimesters with no mention of protein intake.⁵ Nutritional supplements other than folic acid are not recommended. Although additional better-quality research is needed, this review provides some guidance to the family physician on why such counseling matters.

editor's note: The number needed to treat and number needed to harm reported in this Cochrane for Clinicians were calculated by AFP medical editors based on raw data provided in the original Cochrane review.