Abstract
Objectives
To identify if there is an increased risk for spontaneous preterm birth (sPTB) across the continuum of measured, normal cervical lengths (CL) in low-risk women.
Methods
Retrospective cohort study of women with singleton pregnancies and no history of prior sPTB. Women were included if they underwent mid-trimester transvaginal CL measurement between February 2016 and August 2018 and had a measured, normal CL ≥25mm. Women were excluded for progesterone exposure, fetal anomalies, or an unmeasurable CL due to a poorly developed lower uterine segment. The primary study outcome was sPTB <37 weeks. Secondary outcomes included: sPTB <35 weeks, birth gestational age (GA), and the number of hospital evaluations for suspected preterm labor (PTL). Cervical length was considered in interval groups 25–29mm, 30–34mm, 35–39mm, 40–44mm, and ≥45mm. Outcomes were analyzed with χ2 test of trend and as a continuum (linear models, logistic regression and ROC curve), where appropriate.
Results
985 women were included. The incidence of sPTB <37 weeks was 3.7%, with a mean birth GA of 38.7 ± 2.4 weeks. The odds of sPTB <37 weeks decreased with increasing cervical length, considered in 5 mm intervals (odds ratio = 0.67; 95% confidence interval 0.49–0.90) and an increasing birth GA of 1 additional day for each CL increase of 3mm (p = .0002). Conversely, sPTB <35 weeks (p = .49) and mean hospital evaluations for PTL (p = .26) were similar across groups. The ROC curve area-under-the-curve for sPTB <37 weeks of 0.64 showed poor predictive value.
Conclusions
Among women without a history of sPTB, there was an association of decreased risk of sPTB <37 weeks and advanced delivery GA with increasing, but normal-range CL measurements. However, the association was poor and was not associated with spontaneous preterm birth <35 weeks, or the number of hospital evaluations for PTL.
Acknowledgements
The authors thank Mrs. Cherry Neely for her assistance in developing the database used for this project. This abstract was presented at the Society for Maternal-Fetal Medicine 40th Annual Pregnancy Meeting in Grapevine, TX, February 7, 2020.
Disclosure statement
No potential conflict of interest was reported by the author(s).