This is a randomized controlled trial comparing weekly intramuscular injection of 17 alpha hydroxylprogesterone caproate with daily vaginal progesterone in women with singleton pregnancies and history of prior spontaneous preterm birth in terms of maternal, fetal and neonatal outcomes.

Our aim is to assess the effects on maternal, fetal and neonatal outcomes of antenatal progesterone administered intramuscularly versus vaginally in women with singleton pregnancy and a history of prior preterm birth.

This study is intended as a randomized controlled trial. Women with singleton pregnancies between 16 and 20 weeks 6 day will be randomized to one of two treatment groups.

Those randomized to weekly intramuscular progesterone will receive 250 mg of 17 alpha hydroxyprogesterone caproate every week in the clinic between randomization and delivery for those delivery preterm or 36 weeks 6 days.

While those randomized to vaginal progesterone will receive 100 mg vaginal progesterone daily at home. Vaginal progesterone to last between clinic visits will be provided to subject. Those women in the vaginal progesterone group will also be informed on how to obtain additional medication in case of missed clinic appointment. Treatment will be continued until 36 weeks 6 days or as dictated by date of preterm delivery.

Inclusion Criteria:

• Singleton pregnancies
• History of spontaneous preterm brith (between 20 weeks and 36 weeks 6 days)
• Gestational age between 16 weeks 0 days and 20 weeks 6 days.
• Signed consent to participate in the trial

Exclusion Criteria:

• Multiple Gestation
• Prior elective fetal reduction or planned termination
• Known spontaneous reduction to singleton
• Major fetal anomaly or known fetal chromosomal abnormalities
• Progesteone used this pregnancy