Preconception counseling and evaluation are particularly important for women with chronic diseases. Women with diabetes and phenylketonuria should have their diseases under excellent control before conception to prevent miscarriage or birth defects. Counseling of women with asthma, epilepsy, hypertension, and depression can clarify concerns about possible adverse effects on the fetus of the medications used to treat their conditions. Women with a history of venous thrombosis should be assessed for prophylactic treatment during pregnancy, and this is best done before conception. Women with autoimmune diseases, cardiac disease, and renal disease should be assessed for severity of disease and advised of the risks of pregnancy.