Can cervical length predict delivery time?

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Cervical length (CL) measurement is a reliable indicator for predicting preterm delivery in women with threatened preterm labor, according to a retrospective cohort study in The Journal of Maternal-Fetal & Maternal Medicine.

Methods
The Australian study consisted of all women who presented between 22 weeks, 0 days and 35 weeks, 6 days gestation in threatened preterm labor who were admitted for ongoing management to the Royal Brisbane and Women’s Hospital from April 2014 to March 2018.

Management included a transvaginal sonographic CL measurement at time of admission, for which the accuracy of CL for predicting time of delivery was compared between women with a short cervix (CL < 25 mm) and those with a normal cervix (CL ≥ 25 mm).

Results
A total of 146 women with threatened preterm labor met the inclusion criteria, of whom 50.7% had a short cervix and 49.3% had a normal cervix. Mean maternal age was comparable for both groups, as was gestational age at time of presentation (26.7 weeks for a short cervix vs. 26.9 weeks for a normal cervix).

However, the group with a short cervix was more likely to deliver prematurely (before 37 weeks’ gestation), as well as having a shorter time interval between initial presentation and delivery and delivery within 14 days from presentation (P = 0.0002, P = 0.0001 and P = 0.0001, respectively).

For the area under the receiver operator characteristic curves, the CL measurement was also found to be significant for time of delivery before or after 37 weeks (P < 0.0001), preterm delivery before 34 weeks (P = 0.0003) and before 31 weeks (P <  0.0001).

In addition, the CL measurement significantly correlated with preterm delivery within 14 days from presentation ( P< 0.0001).

The CL measurement had a high negative predictive value, ranging from 94.9% to 97.1%, depending on the CL threshold. “The negative predictive value and predictive accuracy of CL as a single measure were of significance,” the authors wrote.

Conclusions
The study’s findings of the statistical significance of sonographic CL alone in predicting time of delivery and the likeliness of delivery within 14 days of presentation could result in cost savings for ongoing management of preterm labor.

A limitation of the current study is its retrospective nature, which makes it impossible to exclude potential confounders such as maternal body mass index (BMI), a history of cigarette smoking or previous preterm birth (PTB) and use of tocolysis. Also, factors like poorly controlled preeclampsia, hypertension, vaginal bleeding, and preterm premature rupture of membranes were not considered.

Nonetheless, the study verifies the findings of previous studies that a sonographic short cervix is a strong predictor of PTB. The authors noted that additional studies are needed to assess combining sonographic CL measurement with other predictive tools like fetal fibronectin in women with symptoms of preterm labor, which might improve the predictive accuracy for PTB.