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Cervical Length Measurement Predicts Preterm Delivery


 

From the Annual Meeting of the American College of Obstetricians and Gynecologists

Major Finding: Measurements of vaginal cervical length using a disposable probe were similar to fetal fibronectin tests in predicting the likelihood of preterm delivery in women with threatened preterm labor.

Data Source: Study of 52 women with threatened preterm labor.

Disclosures: One of Dr. Burwick's associates in the study, Dr. Michael Ross, is medical director of CerviLenz Inc., the company that makes the device, and provided it free to the study. The investigators reported having no other conflicts of interest.

SAN FRANCISCO — A disposable probe that measures vaginal cervical length during speculum examination appeared to be similar in efficacy to fetal fibronectin testing for predicting the likelihood of preterm delivery, in a study of 52 at-risk women.

A cervical length less than 30 mm as measured by the CerviLenz probe correlated with fetal fibronectin positivity and with preterm birth within 7 days, Dr. Richard M. Burwick reported at the meeting.

The sensitivity for preterm delivery within 7 days was 67% with either a CerviLenz measurement of less than 30 mm or fetal fibronectin positivity. The specificity was 83% with the CerviLenz probe and 78% with fetal fibronectin, reported Dr. Burwick, who led the study at Harbor-UCLA Medical Center before moving to Brigham and Women's Hospital, Boston.

The positive predictive value for preterm delivery within 7 days was 22% with a CerviLenz measurement of less than 30 mm and 17% with fetal fibronectin positivity, and the negative predictive value was 97% in each group.

Both measures were less accurate in predicting delivery prior to 37 weeks' gestation. Sensitivity was 29% with a CerviLenz measurement of vaginal cervical length less than 30 mm and 40% with fetal fibronectin positivity. Specificity was 81% and 80%, respectively. The positive predictive value for delivery before 37 weeks was 22% with the CerviLenz measure and 33% with fetal fibronectin results, and the negative predictive value was 85% and 84%, respectively.

“Symptomatic women with a CerviLenz cervical length of less than 30 mm should undergo further observation and consideration of tocolytic and maternal glucocorticoid therapy,” Dr. Burwick said.

Immediate and quantifiable measures of cervical length using the CerviLenz probe may be less variable than the most common way of measuring—by digital exam—and speedier than waiting for fetal fibronectin results, he suggested. The CerviLenz probe also can be used after intercourse or bleeding, he added.

In a previous study by some of the same investigators in the current study, the CerviLenz probe had good predictive value compared with transvaginal ultrasound in identifying women with a cervix shorter than 30 mm (J. Reprod. Med. 2007;52:385-9).

The study enrolled women with singletons at 24-34 weeks' gestational age who were at risk for preterm delivery, with uterine contractions, less than 3 cm cervical dilation, intact membranes, and no vaginal bleeding or recent intercourse. During a speculum examination, fetal fibronectin was collected, cervical length was measured by the CerviLenz probe, and cervical cultures were taken in most patients.

Fetal fibronectin tests in 49 patients were positive in 12 (24%), and CerviLenz measurements were less than 30 mm in 9 of 43 patients (21%). The mean cervical length measurement was 34 mm. The cohort was predominantly Hispanic (38 patients), and 15 patients had a prior preterm birth.

Previous data have shown that only 21%-27% of women with symptoms of preterm labor will have preterm births. Cervical length and cervical effacement help assess preterm birth risk in symptomatic women.

In asymptomatic women, cervical length shorter than 25 mm has been linked to a sixfold increase in risk for preterm birth.

Sensitivity for preterm delivery within 7 days was 67% with either the CerviLenz probe or fetal fibronectin.

Source DR. BURWICK

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