Second trimester uterocervical angle and spontaneous preterm birth in twins.

OBJECTIVE: To determine if there is an association between uterocervical angle (UCA) and spontaneous preterm birth (sPTB) < 37 weeks for women with twins.

MATERIALS AND METHODS: Retrospective cohort study from 2014 to 2017 of twin pregnancies with cervical length (CL) screening between 15 0/7 and 24 6/7 weeks. Monochorionic-monoamniotic twins were excluded. Post-hoc UCA measurements were analyzed as a continuous variable and a wide UCA was also defined as an angle >95° and >110°. The primary outcome was sPTB < 37 weeks. Secondary outcomes were sPTB <34 weeks, <32 weeks, CL, and performance metrics for UCA. Binary logistic regression controlled for age, tobacco use, prior sPTB, CL, and gestational age at CL measurement.

RESULTS: A total of 114 women were studied. The rate of sPTB <37 weeks was 35.0%, <34 weeks was 21.4%, and <32 weeks was 17.1%. As a continuous variable, mean UCA was 117.9° (SD 27.1°) for delivery ≥37 weeks and 133.1° (SD 23.1°) <37 weeks (p = .002). A wider mean UCA was also associated with sPTB <34 weeks (sPTB ≥34 weeks: 120.9° [SD 26.5°] vs. <34 weeks: 133.0° [SD 22.8°], p = .025) and sPTB <32 weeks (sPTB ≥32 weeks: 121.2° [SD 25.9°] vs. <32 weeks: 135.0° [SD 24.0°], p = .018). However, after controlling for age, prior sPTB, tobacco use, CL measurement, and gestational age at CL measurement, UCA was not associated with sPTB <37 weeks, <34 weeks, or <32 weeks. UCA >110° was associated with sPTB <37 weeks after controlling for confounders (aOR 3.6 [95% CI 1.2-10.5], p = 0.02). There was no association between UCA >110° and sPTB <34 or <32 weeks. Furthermore, a UCA >95° was not associated with sPTB <37, <34, or <32 weeks. As a screening tool for sPTB <37 weeks, a UCA of >110° had a sensitivity of 85.7%, specificity of 43.1%, positive predictive value of 53.2%, negative predictive value of 80.0%, positive likelihood ratio of 1.5, and negative likelihood ratio of 0.3.

CONCLUSIONS: In a cohort of dichorionic-diamniotic and monochroionic-diamniotic twins, UCA >110° was associated with sPTB <37 weeks. However, second trimester UCA had a low positive likelihood ratio and was not a robust marker for the prediction of sPTB in twins.