Abstract
Objective: Half of all preterm births occur in women without clinical risk factors. Our goal
was to assess fetal fibronectin assay, Bishop score, and cervical ultrasonography
as screening tests to predict which low-risk pregnancies will end in preterm birth.
Study Design: We performed a secondary analysis of data collected at 22 to 24 weeks’ gestation
from low-risk subjects enrolled in the Preterm Prediction Study, an observational
study of risk factors for preterm birth conducted by the National Institute of Child
Health and Human Development Maternal-Fetal Medicine Units Network. Analysis was limited
to primigravid women and to women who did not have a history of preterm birth or spontaneous
pregnancy loss at <20 weeks’ gestation. Bishop score (≥4), fetal fibronectin level
(≥50 ng/mL), and cervical length (≤25 mm) at 24 weeks’ gestation were evaluated alone
and in sequence as tests to predict spontaneous delivery before 35 weeks’ gestation.
Results: Of the 2929 subjects enrolled in the original study, 2197 (1207 primigravid women
and 900 low-risk multiparous women) met criteria for this analysis. There were 64
spontaneous births before 35 weeks’ gestation (3.04%). All three tests were significantly
related to birth before 35 weeks’ gestation (high Bishop score: relative risk, 3.6;
95% confidence interval, 2.1-6.3; fetal fibronectin detection: relative risk, 8.2;
95% confidence interval, 4.8-13.9; short cervical length: relative risk, 6.9; 95%
confidence interval, 4.3-11.1). However, the sensitivities of the tests alone were
low (23.4% for high Bishop score, 23.4% for fetal fibronectin detection, and 39.1%
for short cervix), as were the sensitivities for Bishop score followed by cervical
ultrasonography (14.1%) and fetal fibronectin assay followed by cervical scan (15.6%).
Conclusion: In the setting of low-risk pregnancy, fetal fibronectin assay and cervical ultrasonography
have low sensitivity for preterm birth before 35 weeks’ gestation. Sequential screening
with Bishop score or fetal fibronectin assay followed by cervical ultrasonography
further decreased sensitivity to only 15% among low-risk women. (Am J Obstet Gynecol
2001;184:652-5.)
Keywords
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References
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Article Info
Publication History
Accepted:
August 31,
2000
Received in revised form:
July 13,
2000
Received:
April 20,
2000
Footnotes
☆Supported by grants HD21410, HD21414, HD21434, HD27860, HD27861, HD27869, HD27883, HD27889, HD27905, HD27915, HD27917, and HD19897 from the National Institute of Child Health and Human Development, Bethesda, Maryland.
☆☆Participating members of the National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network and their institutional affiliations are listed at the end of the article.
★Reprint requests: Jay D. Iams, MD, Department of Obstetrics and Gynecology, The Ohio State University Medical Center, Fifth Floor, Means Hall, 1654 Upham Dr, Columbus, OH 43210.
Identification
Copyright
© 2001 Mosby, Inc. Published by Elsevier Inc. All rights reserved.
