Population differences and the effect of vaginal progesterone on preterm birth in women with threatened preterm labor^*

<p><i>Objective</i>: Threatened preterm labor (tPTL) is a complication of pregnancy. Identification of women and clinical definition differs between countries. This study investigated differences in tPTL and effectiveness of vaginal progesterone to prevent preterm birth (PTB) between two countries.</p> <p><i>Methods</i>: Secondary analysis of a randomized controlled trial (RCT) from Argentina and Switzerland comparing vaginal progesterone to placebo in women with tPTL (<i>n</i> = 379). Cox proportional hazards analysis was performed to compare placebo groups of both countries and to compare progesterone to placebo within each country. We adjusted for baseline differences. Iatrogenic onset of labor or pregnancy beyond gestational age of interest was censored.</p> <p><i>Results</i>: Swiss and Argentinian women were different on baseline. Risks for delivery <14 days and PTB < 34 and < 37 weeks were increased in Argentina compared to Switzerland, HR 3.3 (95% CI 0.62–18), 54 (95% CI 5.1–569) and 3.1 (95% CI 1.1–8.4). In Switzerland, progesterone increased the risk for delivery <14 days [HR 4.4 (95% CI 1.3–15.7)] and PTB <37 weeks [HR 2.5 (95% CI 1.4–4.8)], in Argentina there was no such effect.</p> <p><i>Conclusion</i>: In women with tPTL, the effect of progesterone may vary due to population differences. Differences in populations should be considered in multicenter RCTs.</p

Prevalence of metabolic syndrome, at baseline, three and six months, by randomization group.

<p>Prevalence of metabolic syndrome, at baseline, three and six months, by randomization group.</p

Cardiometabolic outcomes at baseline (mean (standard error (SE))), three and six months for the intervention and control group, unless stated otherwise.

<p>Cardiometabolic outcomes at baseline (mean (standard error (SE))), three and six months for the intervention and control group, unless stated otherwise.</p

Flowchart of participants.

<p>Baseline values are based on number of participants for whom BMI was available. Due to intercurrent pregnancies, or reaching the goal of the intervention prior to 24 weeks (BMI<29 kg/m2 or >5% weight loss) or because participants did not attend the hospital visit, the numbers of participants are decreasing over time.</p

Physical and mental quality of life at baseline, three, six, and 12 months, by randomization group.

<p><b>Abbreviations:</b> QoL, Quality of Life; PCS, Physical Component Score; MCS, Mental Component Score. Values are presented as mean±SE.</p