time for the development of the neural tube is 17 to 30 days after conception.) Subsequently, the Centers for Disease Control (CDC)29 issued specific recommendations for high-dose folic acid supplementation (preconceptionally and throughout the first trimester, under a physician's supervision) to reduce the risk of recurrent neural tube defects. Questions remain concerning the etiology of neural tube defects, the most appropriate dosage, and the appropriate role of nutrition in preventing first occurrences.30,31

Previous delivery of an infant with fetal alcohol syndrome calls for efforts to help the mother eliminate or greatly reduce her consumption of alcoholic beverages, if she has not already done so, and to achieve a healthful diet. (See the later section entitled ''Conditions Involving Unhealthy Behaviors.'')

Extremes of Maternal Weight for Height

The committee found no studies that examined the effects of losing or gaining weight before pregnancy on outcomes of pregnancy. However, because both high and low pregnancy weight are associated with increased risk of various unfavorable pregnancy outcomes, it is prudent to achieve normal weight for height before conception through healthful diet and exercise. Underweight women are at increased risk of delivering a low-birth-weight infant;10 they may also be at increased risk of pregnancy complications such as antepartum hemorrhage, premature rupture of the membranes, preterm delivery, anemia, and endometritis. 32,33 Obese women are at increased risk for complications (e.g., chronic hypertension, preeclampsia, gestational diabetes mellitus, and cesarean delivery34), and their infants are at increased risk for macrosomia or high birth weight—a condition associated with an increased risk of shoulder dystocia and of maternal and infant morbidity. 10

If gastric banding or stapling has been used to treat severe obesity, it is advisable to delay conception until metabolic function and dietary intake have stabilized and there has been time to replenish nutrient stores.35 Both of these types of surgery initially result in greatly reduced food intake; either type can precipitate potentially serious deficiencies of many essential nutrients.

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