Preterm birth remains the leading public health problem in obstetrics. A recent analysis of neonatal mortality (death at age < 28 days) in the United States between 1989 and 2001 revealed that preterm delivery (< 37 weeks) accounted for 70% of neonatal deaths.9 In addition to being at risk for neonatal death, preterm infants are at increased risk for long-term neurologic and developmental morbidity, with an estimated risk of significant handicaps in up to 15% of the survivors. These statistics have led many investigators to identify those women at greatest risk (e.g., those with prior preterm delivery, multiple gestations, maternal weight <50 kg, African-American race, bleeding, and concurrent sexually transmitted diseases). Despite identification of these risk factors, no reproducible and effective method of preventing preterm delivery has been demonstrated. On the contrary, preterm birth rates has risen 27% since 1981.1 A significant contributor to this tremendous rise is the increase in the rate of multiple gestations observed in over the past years. This is partly due to the advances in assisted reproductive technologies with twin gestations accounting for around a quarter of pregnancies conceived following these procedures.