Uterine contraction may not be an independent risk factor for spontaneous preterm birth before 35 weeks in women with cervical shortening

Objective: To compare the risk of spontaneous preterm birth (SPTB) before 35 weeks in symptomatic and asymptomatic women with cervical shortening at 16–34 weeks under mid-trimester universal screening of cervical length (CL). Method: Multicenter retrospective cohort study involving six secondary/tertiary perinatal centers was planned in 2016. Primary outcomes were SPTB before 35 weeks. In all, 407 women were analyzed using multivariable logistic regression analysis for predicting SPTB before 35 weeks while adjusting for presence/absence of uterine contraction, gestational weeks, vaginal bleeding, and CL classification (1–9, 10–14, 15–19, and 20–24 mm) at admission, the execution of cervical cerclage, and the presence/absence of past history of preterm delivery. Results: SPTB before 35 weeks of pregnancy occurred in 14.5%. Presence of uterine contraction was not an independent risk factor for SPTB before 35 weeks (adjusted odds ratio [aOR] 1.22, 95% confidence interval [CI] 0.67–2.20). CL of 1–9 mm, CL of 10–14 mm, and vaginal bleeding at admission were independent risk factors for SPTB before 35 weeks (aOR 5.35, 95% CI 2.11–13.6; aOR 2.79, 95% CI 1.12–6.98; and aOR 2.37, 95% CI 1.12–5.10, respectively). Conclusion: In women with a cervical shortening at 16–34 weeks, presence of uterine contractions at admission may not be an independent risk factor for the occurrence of SPTB before 35 weeks.