title: Prenatal administration of vaginal progesterone and frequency of uterine contractions in asymptomatic twin pregnancies.
abstract: BACKGROUND
  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.
  
  
  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.
authors.affiliation: Department of Obstetrics and Gynecology, São Paulo University Medical School, São Paulo, Brazil.
authors.forename: Lília A M L
authors.identifier: http://orcid.org/0000-0003-2561-0318
authors.initials: LA
authors.lastname: de Oliveira
authors.affiliation: Department of Obstetrics and Gynecology, São Paulo University Medical School, São Paulo, Brazil.
authors.forename: Maria L
authors.identifier: http://orcid.org/0000-0002-6135-4844
authors.initials: ML
authors.lastname: Brizot
authors.affiliation: Department of Obstetrics and Gynecology, São Paulo University Medical School, São Paulo, Brazil.
authors.forename: Adolfo W
authors.identifier: http://orcid.org/0000-0001-6295-5089
authors.initials: AW
authors.lastname: Liao
authors.affiliation: Department of Obstetrics and Gynecology, São Paulo University Medical School, São Paulo, Brazil.
authors.forename: Roberto E
authors.identifier: http://orcid.org/0000-0002-8372-1844
authors.initials: RE
authors.lastname: Bittar
authors.affiliation: Department of Obstetrics and Gynecology, São Paulo University Medical School, São Paulo, Brazil.
authors.forename: Rossana P V
authors.identifier: http://orcid.org/0000-0002-9981-8069
authors.initials: RP
authors.lastname: Francisco
authors.affiliation: Department of Obstetrics and Gynecology, São Paulo University Medical School, São Paulo, Brazil.
authors.forename: Marcelo
authors.identifier: http://orcid.org/0000-0003-1155-2671
authors.initials: M
authors.lastname: Zugaib
mesh_terms: D000282:Administration, Intravaginal; D000328:Adult; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D047928:Premature Birth / Q000517:prevention & control*; D011374:Progesterone / Q000008:administration & dosage*; D011372:Progestins / Q000008:administration & dosage*; D014590:Uterine Contraction / Q000187:drug effects*
chemical_list: D011372:Progestins; D011374:Progesterone
keywords: Twin pregnancy; contraction frequency; progesterone; tocodynamometry; uterine contraction monitoring