Feasibility of a randomized controlled trial testing nifedipine vs. placebo for the treatment of preterm labor

Nifedipine is believed to be a superior tocolytic agent on the basis of efficacy and side-effect profile, but was never prospectively evaluated in a placebo-controlled randomized clinical trial (RCT). In our study, we sought to identify limitations in participation for a would-be RCT comparing nifedipine to placebo.

A prospective feasibility study was conducted at Ste-Justine Hospital, a tertiary care center, on women between 24 and 34 weeks' gestation, presenting to the labor and delivery room with obstetrical complaints. Patient information was collected and would-be participants were identified on the basis of pre-established clinical and ultrasound criteria as well as on willingness to participate, as determined by the study research nurse.

During a 6-month period, 483 women presenting with signs and symptoms of preterm labor (PTL) were eligible for further evaluation. A total of 321 (66.5%) women were excluded for obstetrical and medical reasons whereas 125 (25.9%) did not meet strict inclusion criteria (cervical length <25 mm or positive fetal fibronectin). When using strict criteria, only 37 women (7.6%) were found to be eligible for study participation. Subject willingness to participate as assessed by the research nurse was 50%.

If adhering to strict inclusion/exclusion criteria, the feasibility of an appropriately sampled RCT testing tocolytic therapy against a placebo would require a large concerted multicenter effort to meet sample size demands.