Prematurity is a leading cause of neonatal morbidity and mortality in the USA. Nationally, 12% of all babies deliver before term and 3% deliver before 32 wks gestational age (GA). Recent studies suggest that 17OHP and other progesterone derivatives may reduce the rate of preterm birth among women with a history of prior preterm birth. However, it has not been demonstrated that this reduction in preterm birth is accompanied by a clinically significant reduction in neonatal complications. Further, most women who deliver preterm have no history of a prior preterm birth. Little is known about whether progesterone treatment is effective in women with other risk factors for preterm birth such as multiple gestation. The proposed study will assess the role of 17OHP in women with twin or triplet pregnancies and will assess the impact on neonatal health, not merely the impact on gestational age at delivery. Prior studies were not designed to be large enough to have statistical power to assess effects on neonatal morbidity.