The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network

Jay D. Iams; Robert L. Goldenberg; Paul J. Meis; Brian M. Mercer; Atef Moawad; Anita Das; Elizabeth Thom; Donald McNellis; Rachel L. Copper; Francee Johnson; James M. Roberts

doi:10.1056/NEJM199602293340904

Uterine and Pelvic Conditions Cervical Conditions

The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network

Iams JD, Goldenberg RL, Meis PJ, Mercer BM, Moawad A, Das A, Thom E, McNellis D, Copper RL, Johnson F, Roberts JM

Published February 29, 1996 The New England Journal of Medicine, 334(9), 567-572

DOI 10.1056/NEJM199602293340904 PMID 8569824

RRM Academy Synopsis

A shorter cervix at 24 weeks goes with a higher risk of preterm birth

In a prospective cohort of 2915 women carrying one baby, risk of spontaneous birth before 35 weeks rose as cervical length fell on ultrasound at about 24 weeks. Of the 2915 women, 126 delivered spontaneously before 35 weeks. Risk was highest among the shortest cervixes, those at or below the 1st percentile.

Key Findings

Spontaneous preterm delivery before 35 weeks occurred in 126 of 2915 women (4.3 percent) examined at about 24 weeks; 2531 of them were examined again at about 28 weeks.
At 24 weeks, relative risk against women above the 75th percentile was 1.98 (95 percent confidence interval, 1.20 to 3.27) at or below the 75th percentile (40 mm).
With the same comparison, relative risk at or below the 1st percentile was 13.99 (95 percent confidence interval, 7.89 to 24.78) at 24 weeks and 24.94 (13.81 to 45.04) at 28 weeks.
Using 25 mm as the cutoff at 24 weeks, sensitivity was 37.3 percent, specificity 92.2 percent and positive predictive value 17.8 percent.
In logistic regression, each additional millimeter of cervical length carried an odds ratio for preterm delivery of 0.91 (95 percent confidence interval, 0.89 to 0.93).

Interpretation

This cohort study followed 2915 women carrying one baby, enrolled at 10 university-affiliated prenatal clinics. Cervical length on ultrasound at about 24 weeks was linked with the risk of spontaneous preterm delivery, with the shortest cervixes carrying by far the highest risk. Cerclage is a stitch that closes the cervix. The authors note that their findings raise, but do not resolve, the question of cerclage's role for women with a history of early preterm delivery. The findings support larger studies of cervical-length screening and its use in guiding cerclage decisions.

RRM Context

Restorative reproductive medicine starts with measurement. Cervical length on ultrasound is one such measure. The authors suggest a continuum of cervical performance. Textbooks describe the cervix as either competent or incompetent. Measuring first and labeling second fits the cause-based approach.

Our editorial summary of this paper, not the article's abstract.

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.

Topics

Uterine and Pelvic Conditions › Cervical Conditions › Cervical Insufficiency · Pregnancy › Preterm Birth › Prediction · Birth and Delivery › Birth Outcomes › Maternal Morbidity

Jay D. Iams, Robert L. Goldenberg, Paul J. Meis, Brian M. Mercer, Atef Moawad, Anita Das, Elizabeth Thom, Donald McNellis, Rachel L. Copper, Francee Johnson, James M. Roberts

J Iams, Bob Goldenberg, Rob Goldenberg, Bobby Goldenberg, R Goldenberg, P Meis, B Mercer, A Moawad, A Das, Liz Thom, Beth Thom, Betsy Thom, E Thom, Don McNellis, D McNellis, R Copper, F Johnson, Jim Roberts, Jimmy Roberts, J Roberts

PMID 8569824 8569824 DOI 10.1056/NEJM199602293340904 10.1056/NEJM199602293340904 Iams et al. 1996, Iams 1996

Keywords

Cervix Uteri/anatomy & Histology/diagnostic Imaging, Female, Humans, Obstetric Labor, Premature/epidemiology/etiology, Pregnancy, Pregnancy Trimester, Second, Prospective Studies, Regression Analysis, Risk, Sensitivity and Specificity, Ultrasonography, Prenatal/methods, Uterine Cervical Incompetence/classification/complications/diagnostic Imaging

The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network

A shorter cervix at 24 weeks goes with a higher risk of preterm birth

Key Findings

Interpretation

RRM Context

Abstract

Topics

By this author

Related research

Keywords