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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. [ABSTRACT FROM AUTHOR]

Objectives: To identify whether a poorly developed lower uterine segment (PDLUS) observed during cervical length (CL) screening affects the duration of gestation in women with no prior spontaneous preterm birth (sPTB). Materials and Methods: A retrospective cohort study of women with a singleton gestation and no prior sPTB, who underwent transvaginal CL screening at our institution. We excluded women with progesterone exposure, major anomalies, and women delivering elsewhere. Women with PDLUS were compared to those with a measured (normal) CL ≥25 mm. Primary outcome: birth gestational age (GA). Secondary outcomes: sPTB <35 and 37 weeks, hospital evaluation for preterm labor without delivery, delivery indication, and mode. A Cox proportional‐hazards survival model considered time from CL scan to delivery. We powered the study to detect a one‐half week difference in birth GA. Results: We included 270 women with PDLUS and 985 women with normal CL. Mean birth GA was 38.9 ± 2.0 weeks with PDLUS versus 38.7 ± 2.4 weeks with normal CL (p =.10). Women with PDLUS were less likely to experience sPTB <37 weeks (1.1% vs 3.6%; p = 0.04). There was no difference in sPTB <35 weeks (0.8% vs 1.7%; p =.25). Hospital evaluation for preterm labor (17% vs 19%; p =.54), delivery indication, and mode were not different. The hazard ratio for earlier birth in women with PDLUS was 0.67 (95% CI 0.46, 0.98; p =.04). Conclusions: We observed no difference in mean GA at birth; however, PDLUS was protective against sPTB <37 weeks and was associated with a lower hazard ratio for earlier birth. [ABSTRACT FROM AUTHOR]