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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Article Info
Publication History
Accepted:
March 2,
2004
Received in revised form:
January 23,
2004
Received:
January 23,
2004
for the National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units (see end of article for complete list of participants)Footnotes
☆Supported by grants from the National Institute of Child Health and Human Development (HD 19897, HD 21410, HD 21414, HD 21434, HD 27860, HD 27861, HD 27869, HD 27883, HD 27889, HD 27905, HD 27915, HD 27917, and HD-36801).
☆Reprints not available from the authors.
Identification
Copyright
© 2004 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
