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.