Preterm birth remains a major cause of perinatal morbidity and mortality in developing as well as in developed countries. Despite major clinical research efforts aimed at reducing the incidence of preterm births in the United States, the preterm birth rate reached its highest level in 2 decades, 11.9% in 2001, which translates to a 27% rise since 1981. Much of this increase may be accounted for by the increase in multiple gestations brought about by assisted reproductive technology. Twin gestations accounting for 20% to 25% of all pregnancies conceived following such procedures. Twin gestations are at a particularly increased risk of preterm labor and they deliver at a mean gestational age of 37 weeks compared to 40 weeks for singleton pregnancies. In a study by our group, we estimated that about 54.5% of twin gestations would deliver prior to 37 completed weeks of gestation; i.e. preterm.

Evidence regarding efficacy of interventions designed to prevent preterm birth has been disappointing. Most well-designed clinical trials have failed to demonstrate any reduction in preterm births with such interventions as home uterine activity monitoring, reduced physical activity, administration of antibiotic or tocolytic therapy, and intensive and frequent antenatal follow ups. Recently, progesterone has shown some promise in the prevention of preterm birth among women with prior preterm births. Whether this intervention will prove effective in other populations, such as women with multiple gestations, remains to be seen.

The objective of our study is to compare the effectiveness of weekly intramuscular injections of 17-alpha Hydroxyprogesterone Caproate, a natural metabolite of progesterone, in preventing delivery at less than 37 weeks of gestation in a population of 290 patients with twin gestations between 16 and 36 weeks of gestation compared to a placebo. The data generated will be invaluable in managing this group of patients that is considered at a very high risk for preterm labor and delivery.