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

Frederik Jan Robin Hermans, Ariel Karolinski, Véronique Othenin-Girard, María Victoria Bertolino, Ewoud Schuit, Pablo Salgado, Irene Hösli, Olivier Irion, Cristina Laterra, Ben Willem J. Mol, Begoña Martinez de Tejada

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6 Citations (Scopus)


Objective: 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. Methods: Secondary analysis of a randomized controlled trial (RCT) from Argentina and Switzerland comparing vaginal progesterone to placebo in women with tPTL (n = 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. Results: 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. Conclusion: In women with tPTL, the effect of progesterone may vary due to population differences. Differences in populations should be considered in multicenter RCTs.

Original languageEnglish
Pages (from-to)3223-3228
Number of pages6
JournalThe Journal of Maternal-Fetal and Neonatal Medicine
Issue number19
Publication statusPublished - 1 Oct 2016
Externally publishedYes


  • Harm
  • population differences
  • preterm birth
  • randomized controlled trial
  • secondary analysis
  • selection criteria
  • threatened preterm labor
  • treatment effect
  • treatment interaction
  • vaginal progesterone

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