Maternal obesity, uterine activity, and the risk of spontaneous preterm birth.
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.
Ehrenberg
Hugh M
HM
* 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.
Iams
Jay D
JD
Goldenberg
Robert L
RL
Newman
Roger B
RB
Weiner
Steven J
SJ
Sibai
Baha M
BM
Caritis
Steve N
SN
Miodovnik
Menachem
M
Dombrowski
Mitchell P
MP
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