Exposure of a woman to either excessive or inadequate amounts of certain nutrients early in the first trimester of pregnancy may lead to spontaneous abortion or congenital malformations. Exposure to high, potentially harmful amounts of a nutrient is possible under several circumstances: if the woman has a metabolic condition (such as diabetes mellitus or phenylketonuria) that causes excessive maternal blood levels of one or more nutrients; if the mother takes high doses of retinol (preformed vitamin A); or if she takes a potentially teratogenic medication such as isotretinoin (a vitamin A analogue). Very low nutrient levels are possible if the mother's diet is chronically inadequate or if she takes certain medications or other substances that alter her metabolism or deplete her nutritional stores. For example, the medicines methotrexate and diphenylhydantoin (Dilantin ^®) alter folate metabolism, and alcohol increases the urinary excretion of zinc. For more information on these topics, see, for example, Berkowitz and colleagues,⁸ Briggs and others,⁹ the 1990 Institute of Medicine report Nutrition During Pregnancy,¹⁰ and Niebyl.¹¹

Women whose pregnancies are complicated by preexisting diabetes mellitus are at increased risk for delivering infants with major congenital malformations.¹² These malformations occur in the first weeks after conception, often well before many women enter prenatal care. Many of these anomalies, however, may be prevented by the normalization of maternal blood glucose values throughout the first 12 weeks of gestation.¹³ For blood glucose values to be normal at conception, it is desirable to provide the nutrition and medical services needed to achieve metabolic control well before conception.^14,15 In one recent study that involved intensive education and treatment, the incidence of major congenital anomalies in the group treated before conception was 1.2%, compared with 10.9% in the group treated at 6 weeks of gestation or later.¹⁶ Scheffler and colleagues¹⁷ reported that early enrollment (before 8 weeks' gestation) in the California Diabetes and Pregnancy Program, which has a strong nutrition component, had a high cost-benefit ratio: for each $1 spent on the program, the estimated short-term savings exceeded $5.