Mid-Trimester Cervical Length Screening: Effect of Poorly Developed Lower Uterine Segment on Pregnancy Outcome.

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.