More than 500,000 of the 4 million neonates born each year in this country are born before 37 weeks' gestation, a preterm birth rate of 12.7%.1 This public health problem has been growing steadily since 1981, and its solution has eluded researchers and clinicians.

Preterm birth now contributes to more than one-third of all infant deaths.2 Tocolytic therapies have been used for many years to delay delivery but have not been shown to improve neonatal outcomes.3 In a 5-year, randomized, double-blind, placebo-controlled trial involving 153 women in preterm labor, researchers found that transdermal nitroglycerin led to a significant decrease in undesirable neonatal outcomes.3 The primary outcome measure in this study was a composite of neonatal morbidity, including chronic lung disease, severe intraventricular hemorrhage, periventricular leukomalacia, necrotizing enterocolitis, and perinatal mortality. Treatment with nitroglycerin resulted in a significantly decreased incidence of composite neonatal outcomes compared with placebo, primarily with the use of nitroglycerin before 28 weeks' gestation. The number needed to treat (NNT) was 10. There was a nonsignificant decreased risk of delivery before 28 weeks' gestation and a nonsignificant prolongation of 7.2 days of the pregnancy in the nitroglycerin-treated group compared with the placebo group. In a subgroup of mothers who began labor before 28 weeks' gestation, pregnancies were found to last a mean of 23.4 days longer. More maternal side effects occurred with the use of nitroglycerin in the form of maternal headaches.

The beneficial effect of nitroglycerin on neonatal outcomes was due to a prolongation of pregnancy, but a potential nontocolytic effect of nitroglycerin on uterine and placental blood flow cannot be eliminated.3 Nitroglycerin delays delivery by relaxing the smooth muscles of the uterus and may also improve blood flow to the uterus and placenta.

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