Update on prenatal care.

Many elements of routine prenatal care are based on tradition and lack a firm evidence base; however, some elements are supported by more rigorous studies. Correct dating of the pregnancy is critical to prevent unnecessary inductions and to allow for accurate treatment of preterm labor. Physicians should recommend folic acid supplementation to all women as early as possible, preferably before conception, to reduce the risk of neural tube defects. Administration of Rho(D) immune globulin markedly decreases the risk of alloimmunization in an RhD-negative woman carrying an RhD-positive fetus. Screening and treatment for iron deficiency anemia can reduce the risks of preterm labor, intrauterine growth retardation, and perinatal depression. Testing for aneuploidy and neural tube defects should be offered to all pregnant women with a discussion of the risks and benefits. Specific genetic testing should be based on the family histories of the patient and her partner. Physicians should recommend that pregnant women receive a vaccination for influenza, be screened for asymptomatic bacteriuria, and be tested for sexually transmitted infections. Testing for group B streptococcus should be performed between 35 and 37 weeks' gestation. If test results are positive or the patient has a history of group B streptococcus bacteriuria during pregnancy, intrapartum antibiotic prophylaxis should be administered to reduce the risk of infection in the infant. Intramuscular or vaginal progesterone should be considered in women with a history of spontaneous preterm labor, preterm premature rupture of membranes, or shortened cervical length (less than 2.5 cm). Screening for diabetes should be offered using a universal or a risk-based approach. Women at risk of preeclampsia should be offered low-dose aspirin prophylaxis, as well as calcium supplementation if dietary calcium intake is low. Induction of labor may be considered between 41 and 42 weeks' gestation.