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Frequency of uterine contractions in asymptomatic pregnant women with or without a short cervix on transvaginal ultrasound scan

  • Vincenzo Berghella
    Affiliations
    Departments of Obstetrics and Gynecology at Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pa,a Ohio State University, Columbus, Ohio,b the Medical University of South Carolina, Charleston, SC,cBiostatistics Center at George Washington University, Washington, DC,d the University of Alabama, Birmingham, Ala,e Wake Forest University, Winston-Salem, NC,f University of Pittsburgh-Magee Women's Hospital, Pittsburgh, Pa,g and Wayne State University, Detroit, MichhUSA
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  • Jay D. Iams
    Affiliations
    Departments of Obstetrics and Gynecology at Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pa,a Ohio State University, Columbus, Ohio,b the Medical University of South Carolina, Charleston, SC,cBiostatistics Center at George Washington University, Washington, DC,d the University of Alabama, Birmingham, Ala,e Wake Forest University, Winston-Salem, NC,f University of Pittsburgh-Magee Women's Hospital, Pittsburgh, Pa,g and Wayne State University, Detroit, MichhUSA
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  • Roger B. Newman
    Affiliations
    Departments of Obstetrics and Gynecology at Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pa,a Ohio State University, Columbus, Ohio,b the Medical University of South Carolina, Charleston, SC,cBiostatistics Center at George Washington University, Washington, DC,d the University of Alabama, Birmingham, Ala,e Wake Forest University, Winston-Salem, NC,f University of Pittsburgh-Magee Women's Hospital, Pittsburgh, Pa,g and Wayne State University, Detroit, MichhUSA
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  • Cora MacPherson
    Affiliations
    Departments of Obstetrics and Gynecology at Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pa,a Ohio State University, Columbus, Ohio,b the Medical University of South Carolina, Charleston, SC,cBiostatistics Center at George Washington University, Washington, DC,d the University of Alabama, Birmingham, Ala,e Wake Forest University, Winston-Salem, NC,f University of Pittsburgh-Magee Women's Hospital, Pittsburgh, Pa,g and Wayne State University, Detroit, MichhUSA
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  • Robert L. Goldenberg
    Affiliations
    Departments of Obstetrics and Gynecology at Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pa,a Ohio State University, Columbus, Ohio,b the Medical University of South Carolina, Charleston, SC,cBiostatistics Center at George Washington University, Washington, DC,d the University of Alabama, Birmingham, Ala,e Wake Forest University, Winston-Salem, NC,f University of Pittsburgh-Magee Women's Hospital, Pittsburgh, Pa,g and Wayne State University, Detroit, MichhUSA
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  • Eberhard Mueller-Heubach
    Affiliations
    Departments of Obstetrics and Gynecology at Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pa,a Ohio State University, Columbus, Ohio,b the Medical University of South Carolina, Charleston, SC,cBiostatistics Center at George Washington University, Washington, DC,d the University of Alabama, Birmingham, Ala,e Wake Forest University, Winston-Salem, NC,f University of Pittsburgh-Magee Women's Hospital, Pittsburgh, Pa,g and Wayne State University, Detroit, MichhUSA
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  • Steve N. Caritis
    Affiliations
    Departments of Obstetrics and Gynecology at Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pa,a Ohio State University, Columbus, Ohio,b the Medical University of South Carolina, Charleston, SC,cBiostatistics Center at George Washington University, Washington, DC,d the University of Alabama, Birmingham, Ala,e Wake Forest University, Winston-Salem, NC,f University of Pittsburgh-Magee Women's Hospital, Pittsburgh, Pa,g and Wayne State University, Detroit, MichhUSA
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  • Mitchell P. Dombrowski
    Affiliations
    Departments of Obstetrics and Gynecology at Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pa,a Ohio State University, Columbus, Ohio,b the Medical University of South Carolina, Charleston, SC,cBiostatistics Center at George Washington University, Washington, DC,d the University of Alabama, Birmingham, Ala,e Wake Forest University, Winston-Salem, NC,f University of Pittsburgh-Magee Women's Hospital, Pittsburgh, Pa,g and Wayne State University, Detroit, MichhUSA
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      Abstract

      Objective

      The purpose of this study was to compare the frequency of uterine contractions in asymptomatic pregnant women with and without a short cervix (<25 mm) on transvaginal ultrasound (TVU) and to determine the additive risk of contractions on the risk of preterm birth.

      Study design

      The study involved secondary analysis of a blinded observational study of asymptomatic singleton pregnancies who were at high risk for preterm birth and who received both home uterine activity monitoring daily and transvaginal ultrasound of the cervix at 22 to 24 and 27 to 28 weeks of gestation. Thresholds for the maximum frequency of uterine contractions of 4 per hour and transvaginal ultrasound cervical length of 25 mm were used for analysis. Contraction frequency was compared in women with cervical length <25 mm and ≥25 mm and was correlated with the risk of spontaneous preterm birth at <35 weeks of gestation.

      Results

      Of the 303 women whose pregnancy was evaluated at 22 to 24 weeks of gestation, the 39 women (13%) with a cervical length of <25 mm had 1.6 ± 2.7 versus 1.2 ± 2.0 contractions per hour in the 264 women (87%) with a cervical length of ≥25 mm (P = .37). At 27 to 28 weeks of gestation (n = 295 women), contraction frequency was 3.2 ± 3.7 versus 2.8 ± 3.1 contractions per hour in women with a cervical length of <25 mm (n = 59 women; 20%) versus those with a cervical length of ≥25 mm (n = 236 women; 80%; P = .34). Among women with a short cervix, the relative risks for spontaneous preterm birth were 2.0 (95% CI, 0.95-4.2) and 2.1 (95% CI, 1.06-4.3) for women with ≥4 contractions per hour compared with women with <4 contractions per hour at 22 to 24 and 27 to 28 weeks of gestation, respectively. Results were confirmed by logistic regression analysis.

      Conclusion

      The frequency of uterine contractions in asymptomatic women was not related significantly to cervical length of <25 mm versus ≥25 mm. Among women with a cervical length of <25 mm at 22 to 24 or 27 to 28 weeks of gestation, there was a trend toward a 2-fold increased risk of spontaneous preterm birth when the maximum contraction frequency was ≥4 per hour, compared to <4 per hour.

      Keywords

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