17OHP for Reduction of Neonatal Morbidity Due to Preterm Birth (PTB) in Twin and Triplet Pregnancies

Inclusion Criteria: 1. Gestational age (GA) 15-23w0d gestational age at the time of recruitment 2. GA 16w0dk to 23w6d at the time of randomization and initiation of injections 3. Maternal age 18 years or older 4. One of these risk factors for spontaneous preterm birth: 1. Twins in current pregnancy, dichorionic placentation 2. Triplets in current pregnancy, trichorionic placentation 5. Intact membranes 6. Patient has had at least one detailed 2nd-trimester ultrasound examination documenting placentation, chorionicity, fetal number, fetal size, amniotic fluid volumes, and fetal anatomy. (This examination must comply with minimum standards such as those published by the American Institute of Ultrasound in Medicine, American College of Radiology, or American College of Obstetricians \& Gynecologists It is NOT mandatory that this examination be performed at the research-study center.) 7. Investigator believes patient will be reliable with follow-up visits and believes that delivery data and neonatal data are likely to be available. Exclusion Criteria: 1. Symptomatic uterine contractions in current pregnancy 2. Contraindication to interventions intended to prolong the pregnancy (including lethal fetal anomalies, amnionitis, preeclampsia, severe oligohydramnios, severe growth delay, fetal death appears imminent or inevitable) 3. Risk factors for major neonatal morbidity unrelated to preterm delivery (such as monochorionic placentation in multiple gestation, major malformations, certain medication exposures) 4. Preexisting maternal medical condition that might be worsened by progesterone therapy, including: asthma requiring medications, renal insufficiency, seizure disorder, ischemic heart disease, active cholecystitis, impaired liver function, history of thromboembolic disorder, history of breast cancer, history of major depression requiring hospitalization. 5. Preexisting maternal medical condition associated with a high risk of preterm delivery including: refractory hypertension, diabetes with nephropathy or retinopathy, renal insufficiency, active systemic lupus erythematosus. Note that a history of prior preterm birth is NOT an exclusion. 6. Use of progesterone or progesterone-derivative medication after 15 weeks gestation in current pregnancy. 7. Allergy to 17OHP or oil vehicle. 8. Placement of emergent cerclage (defined as one placed after the occurrence of cervical change such as dilation, funneling, or effacement) with this pregnancy. Prophylactic cerclage is NOT an exclusion (defined as one placed before any cervical change, for example, because of a history of cervical incompetence, or because of a prior cervical procedure such as LEEP or cone biopsy).