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Previous Volume 334:567-573 February 29, 1996 Number 9 Next

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ABSTRACT

Background The role of the cervix in the pathogenesis of premature delivery is controversial. In a prospective, multicenter study of pregnant women, we used vaginal ultrasonography to measure the length of the cervix; we also documented the incidence of spontaneous delivery before 35 weeks' gestation.

Methods At 10 university-affiliated prenatal clinics, we performed vaginal ultrasonography at approximately 24 and 28 weeks of gestation in women with singleton pregnancies. We then assessed the relation between the length of the cervix and the risk of spontaneous preterm delivery.

Results We examined 2915 women at approximately 24 weeks of gestation and 2531 of these women again at approximately 28 weeks. Spontaneous preterm delivery (at less than 35 weeks) occurred in 126 of the women (4.3 percent) examined at 24 weeks. The length of the cervix was normally distributed at 24 and 28 weeks (mean [±SD], 35.2±8.3 mm and 33.7±8.5 mm, respectively). The relative risk of preterm delivery increased as the length of the cervix decreased. When women with shorter cervixes at 24 weeks were compared with women with values above the 75th percentile, the relative risks of preterm delivery among the women with shorter cervixes were as follows: 1.98 for cervical lengths at or below the 75th percentile (40 mm), 2.35 for lengths at or below the 50th percentile (35 mm), 3.79 for lengths at or below the 25th percentile (30 mm), 6.19 for lengths at or below the 10th percentile (26 mm), 9.49 for lengths at or below the 5th percentile (22 mm), and 13.99 for lengths at or below the 1st percentile (13 mm) (P<0.001 for values at or below the 50th percentile; P = 0.008 for values at or below the 75th percentile). For the lengths measured at 28 weeks, the corresponding relative risks were 2.80, 3.52, 5.39, 9.57, 13.88, and 24.94 (P<0.001 for values at or below the 50th percentile; P = 0.003 for values at the 75th percentile).

Conclusions The risk of spontaneous preterm delivery is increased in women who are found to have a short cervix by vaginal ultrasonography during pregnancy.

Source Information

From the Departments of Obstetrics and Gynecology at Ohio State University, Columbus (J.D.I., F.J.), the University of Alabama, Birmingham (R.L.G., R.L.C.), Bowman Gray School of Medicine, Winston-Salem, N.C. (P.J.M.), the University of Tennessee, Memphis (B.M.M.), and the University of Chicago, Chicago (A.M.); the Biostatistics Center, George Washington University, Washington, D.C. (A.D., E.T.); the National Institute of Child Health and Human Development (NICHD), Bethesda, Md. (D.M.); and the University of Pittsburgh, Pittsburgh (J.M.R.). Other contributing authors were Menachem Miodovnik, M.D. (University of Cincinnati, Cincinnati), J. Peter Van Dorsten, M.D. (Medical University of South Carolina, Charleston), Steve N. Caritis, M.D. (University of Pittsburgh, Pittsburgh), Gary R. Thurnau, M.D. (University of Oklahoma, Oklahoma City), and Sidney F. Bottoms, M.D. (Wayne State University, Detroit).

Address reprint requests to Dr. Iams at the Department of Obstetrics and Gynecology, Ohio State University, 1654 Upham Dr., Columbus, OH 43210.

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