To compare the tocolytic efficacy oxytocin receptor antagonist (Atosiban) with that of calcium channel blockers (Nifedipine) among women with multiple gestation who present with threatened preterm labor.

Preterm birth remains the principal cause of early neonatal death. Infants born preterm (before 37 weeks' gestation) often suffer significant immediate morbidity and need lengthy stays in neonatal intensive care units. Moreover, there is a significant risk of long-term neurological morbidity in a proportion of the survivors. Patients with a multiple gestation are at significant risk for preterm labor and delivery as approximately 60% of all those pregnancies will be delivered preterm.

A number of oxytocin receptor antagonists have been developed, and of these, three, atosiban, barusiban and retosiban have been investigated in humans as tocolytic agents. To date, only atosiban is in use outside of clinical trials. Atosiban is an oxytocin receptor antagonist which was specifically developed for the treatment of preterm labor. Early reports of the use of Atosiban for tocolysis showed promise both in vitro and in animal studies, and preliminary studies in pregnant and non-pregnant humans suggested a very low incidence of maternal side effects .

Inclusion Criteria:

1. Twin pregnancy
2. Gestational age between 24+0 and 32+6 weeks
3. Intact amniotic membranes
4. Threatened preterm labor
5. Age 18-50.

Exclusion Criteria:

1. Rupture of membranes
2. Vaginal bleeding resulting from placenta previa or placental abruption
3. Fever above 38°C
4. Severe preeclampsia
5. Maternal cardiovascular or liver diseases
6. Systolic blood pressure less than 90 mm Hg
7. Known uterine malformation
8. Intrauterine growth restriction below the fifth percentile
9. Non-reassuring fetal status
10. Antepartum diagnosis of major fetal malformations
11. Fetal death
12. Previous tocolytic therapy or Betamethasone treatment