Here is the design of a clinical trial:

Official Title: Tocolysis in the Management of Preterm Premature Rupture of Membranes Before 34 Weeks of Gestation: a Double-blinded Randomized Controlled Trial

Included conditions:
- Preterm Premature Rupture of Membrane

Study Armgroups:
- {'label': 'Nifedipine', 'type': 'ACTIVE_COMPARATOR', 'interventionNames': ['Drug: Nifedipine']}
- {'label': 'Placebo', 'type': 'PLACEBO_COMPARATOR', 'interventionNames': ['Drug: Placebo of Nifedipine']}

Interventions:
- {'type': 'DRUG', 'name': 'Nifedipine', 'description': 'Loading dose: Oral Nifedipine 20 mg prolonged-release at T0 and T0.5 (i.e. 30 min), total=2x20 mg Maintenance dose: Oral Nifedipine 20 mg prolonged-release at T3, then 1 pill every 8 hr for 48 hr (i.e. T11, T19, T27, T35 and T43, total=6x20 mg)', 'armGroupLabels': ['Nifedipine']}
- {'type': 'DRUG', 'name': 'Placebo of Nifedipine', 'description': 'Oral Placebo of Nifedipine 20 mg, at T0, T0.5, T3, T11, T19, T27, T35 and T43', 'armGroupLabels': ['Placebo']}

Primary Outcomes:
- {'measure': 'Perinatal morti-morbidity', 'description': 'Composite outcome including fetal death, neonatal death and/or neonatal severe morbidity (mechanical ventilation ≥ 48 hrs, severe bronchopulmonary dysplasia, severe intraventricular hemorrhage, cystic periventricular leucomalacia, neonatal early-onset sepsis, necrotizing enterocolitis, retinopathy of prematurity).', 'timeFrame': 'Up to discharge from hospital, with a maximum of 24 weeks after birth.'}

Please estimate the sample size based on the assumption: 
We assume an alpha-risk of 0.05 and a beta-risk of 0.20 (i.e., statistical power of 80%).
Sample size
          Within the prospective, national, population-based EPIPAGE-2 cohort study of preterm births, we selected a sample of 888 women according to the TOCOPROM eligibility criteria and estimated the frequency of infants diagnosed with any criterion of the composite primary outcome to be 35.5%. This is an average estimate taking into account the expected variation of gestational age at birth in our study population from 22 to 37+ weeks. This estimate is consistent with findings in recent studies [15, 52, 66].
          We hypothesized that the beneficial effect of tocolysis would be mediated by both higher gestational age at birth and the administration of a complete course of antenatal corticosteroids. The EPIPAGE-2 study showed that among women with PPROM, each one-day increase in gestational age at birth is significantly associated with a reduced relative risk (RR) of fetal or neonatal death or severe morbidity (RR 0.95, 95% CI 0.91â0.99) [10]. With pregnancy prolonged by 48âh by effective tocolysis, we expect to reduce the rate of fetal or neonatal death or severe morbidity by 10%. Each additional day after the initial 48-h period will also contribute to reducing adverse outcomes. Moreover, this initial prolongation will allow a complete course of antenatal corticosteroids, with additional beneficial effects, as shown by Roberts et al. [28, 67]. In meta-analyses of women with PPROM, antenatal steroids have been associated with reduced perinatal (RR 0.59, 95%CI 0.39â0.90) and neonatal mortality (RR 0.61, 0.46-0.83), respiratory distress syndrome (RR 0.70, 0.55-0.90), chronic lung disease (RR 0.50, 0.33â0.76), necrotizing enterocolitis (RR 0.39, 0.18â0.86), and IVH (RR 0.47, 0.28-0.79). Retinopathy of prematurity, early-onset sepsis, and periventricular leukomalacia were not analyzed separately by membrane status in these meta-analyses.
          When we assume an alpha-risk of 0.05 and a beta-risk of 0.20 (i.e., statistical power of 80%), 702 women (351 per arm) are required to show a reduction of the primary endpoint from 35% (placebo group) to 25% (nifedipine group). We plan to increase the required number of subjects by 20%, to replace patients who leave the study early. The total number of subjects required is thus 850.