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Am Fam Physician. 2004;70(7):1359

Clinical Question: Does ultrasonographic screening for a short cervix at 22 to 24 weeks of gestation, followed by prophylactic cerclage in women who screen positive, reduce the rates of preterm birth?

Setting: Outpatient (specialty)

Study Design: Randomized controlled trial (nonblinded)

Allocation to Groups: Concealed

Synopsis: While previous studies of cerclage to prevent preterm birth in women with incompetent cervix have had conf licting results, this was the first study to undertake large-scale population screening (N = 47,123 from 12 hospitals in six countries). Women with an ultrasonographic finding of a cervical length of 15 mm or less at 22 to 24 weeks of gestation were eligible to participate in the intervention study. A total of 470 women met the selection criteria, 253 (54 percent) of whom agreed to participate in a randomized trial of cerclage versus expectant management. Analysis was by intention to treat; very few women did not receive the assigned treatment or were lost to follow-up.

The proportion of women with a preterm birth at less than 33 weeks of gestation was 22 percent in the cerclage group and 26 percent in the control group, which was not statistically significant. The study was powered to detect a 20-percent absolute risk difference that was expected based on pilot data. Stillbirths and perinatal deaths were 8 percent in the cerclage group and 12 percent in the control group. This would be a clinically significant difference, but the study was not large enough to determine whether it was a true difference. There were no significant differences in neonatal blood cultures, brochopulmonary dysplasia, intraventricular hemorrhage, retinopathy of prematurity, maternal pyrexia, or symptomatic vaginal discharge.

Bottom Line: Ultrasonographic screening for cervical length of 15 mm or less at 22 to 24 weeks of gestation identifies women at risk of preterm delivery at less than 33 weeks. A 4-percent absolute risk reduction for early preterm births was not statistically significant in the group treated with prophylactic cerclage but may be considered clinically significant if proved. The study was too small to detect clinically important differences in perinatal morbidity and mortality. (Level of Evidence: 1b–)

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