A randomized prospective trial has shown that folic acid started before conception and continued for the first trimester reduces the risk of recurrence of neural tube defects by 72% in women with a previously affected child. Carbamazepine exposure in utero is associated with a 1% risk of spina bifida. Long-term follow-up of antenatal exposure to phenobarbital and carbamazepine in two groups of infants shows no neurologic differences between the two groups. Magnesium sulfate is more effective in prevention of recurrent eclamptic seizures than phenytoin. During pregnancy, the need for thyroxine increases in many women. Vitamin B6 and ginger are both effective for nausea and vomiting in early pregnancy. Low-dose aspirin does not change the course of preeclampsia when it is started after the diagnosis is made. Angiotensin-converting enzyme inhibitors cause significant disturbances of fetal and neonatal renal function. Prophylactic beta-adrenergic agents fail to prevent prematurity in twins. Oral tocolysis with magnesium chloride or ritodrine is no more effective than observation alone. The risk of primary pulmonary hypertension in the newborn after indomethacin tocolysis is increased with prolonged therapy. Lithium causes polyhydramnios from fetal diabetes insipidus in utero. Treatment of Ureaplasma urealyticum infection with erythromycin during pregnancy does not eliminate the organism from the lower genital tract and does not improve perinatal outcome.