Diet and patterns of eating during pregnancy can affect perinatal outcomes through direct physiologic effects or by stressing the fetus in ways that permanently affect phenotype. Supplements are not a magic nutritional remedy, and evidence of profound benefit for most supplements remains inconclusive. However, research supports calcium supplements to decrease preeclampsia. Following a low glycemic, Mediterranean-type diet appears to improve ovulatory infertility, decrease preterm birth, and decrease the risk of gestational diabetes. Although women in the United States have adequate levels of most nutrients, subpopulations are low in vitamin D, folate, and iodine. Vitamin D has increasingly been shown to be important not only for bone health, but also for glucose regulation, immune function, and good uterine contractility in labor. To ensure adequate vitamin and micronutrient intake, especially of folate before conception, all reproductive age women should take a multivitamin daily. In pregnancy, health care providers need to assess women's diets, give them weight gain recommendations based on their body mass index measurement, and advise them to eat a Mediterranean diet rich in omega-3 fatty acids (ingested as low–mercury risk fatty fish or supplements), ingest adequate calcium, and achieve adequate vitamin D levels through sun exposure or supplements. Health care providers should continue to spend time on nutrition assessment and counseling.