title: Maternal obesity, uterine activity, and the risk of spontaneous preterm birth.
abstract: OBJECTIVE
  To assess the associations among maternal obesity, uterine contraction frequency, and spontaneous preterm birth in women at risk for spontaneous preterm birth.
  
  
  METHODS
  In a secondary analysis, we analyzed data from 253 women at risk for spontaneous preterm birth (prior spontaneous preterm birth, vaginal bleeding) enrolled in a multicenter observational study of home uterine activity monitoring at 11 centers. All women wore a uterine activity monitor twice daily from 22 weeks through 34 weeks of gestation. Mean and maximal contractions/hour at 22-24, 25-26, 27-28, 29-30, 31-32 weeks, and at or after 33 weeks of gestation were compared between overweight/obese women (a body mass index [BMI] at 22-24 weeks greater than 25 kg/m) and normal/underweight women (a BMI of 25 kg/m or less) at each gestational age interval. Multivariable analysis evaluated the influences of BMI, contractions, fetal fibronectin, and transvaginal cervical length on spontaneous preterm birth before 35 weeks.
  
  
  RESULTS
  Obese/overweight women (n=156) were significantly less likely to experience spontaneous preterm birth before 35 weeks (8.3% compared with 21.7%, P<.01). For each gestational age interval before 32 weeks, obese/overweight women had fewer mean contractions/hour (P<.01 for each) and maximal contractions/hour (P<.01 for each) than normal/underweight women, although their mean cervical lengths (34.3 mm compared with 33.1 mm, P=.25), and fetal fibronectin levels (7.1% compared with 7.2% 50 ng/mL or more, P=.97) were similar at study enrollment. Obese/overweight status was associated with a lower risk of spontaneous preterm birth before 35 weeks after controlling for contraction frequency and other factors evaluated at 22-24 weeks, but not at later periods.
  
  
  CONCLUSIONS
  Obese/overweight women at risk for spontaneous preterm birth exhibit less uterine activity and less frequent spontaneous preterm birth before 35 weeks of gestation than normal/underweight women.
  
  
  METHODS
  II.
authors.affiliation: * For the other members of the NICHD MFMU who participated in this study, see the Appendix online at http://links.lww.com/A617. From the Case Western Reserve University-MetroHealth Medical Center, Cleveland, Ohio; Ohio State University, Columbus, Ohio; Drexel University, Philadelphia, Pennsylvania; Medical University of South Carolina, Charleston, South Carolina; George Washington University Biostatistics Center, Washington, DC; University of Tennessee, Memphis, Tennessee; University of Pittsburgh, Pittsburgh, Pennsylvania; University of Cincinnati, Cincinnati, Ohio; and Wayne State University, Detroit, Michigan.
authors.forename: Hugh M
authors.initials: HM
authors.lastname: Ehrenberg
authors.forename: Jay D
authors.initials: JD
authors.lastname: Iams
authors.forename: Robert L
authors.initials: RL
authors.lastname: Goldenberg
authors.forename: Roger B
authors.initials: RB
authors.lastname: Newman
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Weiner
authors.forename: Baha M
authors.initials: BM
authors.lastname: Sibai
authors.forename: Steve N
authors.initials: SN
authors.lastname: Caritis
authors.forename: Menachem
authors.initials: M
authors.lastname: Miodovnik
authors.forename: Mitchell P
authors.initials: MP
authors.lastname: Dombrowski
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D009765:Obesity / Q000150:complications*; D007752:Obstetric Labor, Premature / Q000209:etiology* / Q000503:physiopathology; D011247:Pregnancy; D011248:Pregnancy Complications; D012307:Risk Factors; D014590:Uterine Contraction