RESUMO
INTRODUCTION: A previous study indicated that progesterone reduces the mean uterine contraction frequency in singleton pregnancy at high risk for preterm birth. The aim of this study was to investigate the effect of vaginal progesterone on the frequency of uterine contractions in twin pregnancies. MATERIAL AND METHODS: This was a secondary analysis of a randomized, double-blind, placebo-controlled trial of twin pregnancies exposed to vaginal progesterone or placebo. Naturally conceived twin pregnancies with no prior history of preterm delivery, asymptomatic regarding preterm labor, who had undergone uterine contraction frequency monitoring from 24 to 34 weeks and 6 days were included in the study. Comparison of the mean frequency of uterine contractions between the treatment groups was performed. We also examined the influence of cervical length and chorionicity on the mean frequency of uterine contractions according to the group. RESULTS: The final analysis included 166 women in the progesterone and 170 in the placebo group. The baseline characteristics were similar in the two groups. Overall, no difference in the mean frequency of uterine contractions (p = 0.91) was observed between the progesterone (2.54 ± 3.19) and placebo (2.56 ± 3.59) groups. Also, no difference in the mean frequency of uterine contractions was observed between the groups in each week between 24 and 34 weeks and 6 days of gestation. Cervical length and chorionicity did not influence the frequency of contractions according to the progesterone or placebo treatment. CONCLUSIONS: Overall, progesterone does not influence the frequency of uterine contractions in twin pregnancies.