Introduction: There is a paucity of data on the risk of preterm birth subcategorized by gestational age in pregnancies after the pre-pregnancy excisional treatment for cervical lesions. In addition, little is known about the effect of prophylactic cerclage on the risk of preterm birth. The aim of this study was to investigate the risk of preterm birth stratified by gestational period and its reduction by the prophylactic cerclage in women with prior excisional surgery. Materials and methods: We retrospectively analyzed a cohort of singleton pregnancies in the Japan Perinatal Registry Network Database (2013–2014, n = 307,001). Cases included pregnancies after the surgery (i.e. conization and loop electrosurgical excision procedure). Controls comprised the propensity-score matched pregnancies without pre-pregnancy surgery. The main outcome was the occurrence of preterm birth. The effect of prophylactic cervical cerclage on the risk of preterm birth after the excisional surgery was also examined using cases. Results: In the propensity-score matched population (cases, n = 1389; controls, n = 1389), cases exhibited a higher risk of preterm birth and preterm prelabor rupture of membranes (PROM), compared with controls (preterm birth: 25.3 versus 10.6%; preterm PROM: 14.0 versus 3.5%: both p <.0001). Odds ratios (OR; 95% confidence interval [CI]) for preterm birth at 22–27 weeks, 28–31 weeks, 32–33 weeks, and 34–36 weeks were 3.4 [1.8–6.5], 4.6 [2.7–7.7], 2.2 [1.4–3.5], and 2.1 [1.6–2.7], respectively. The association was stronger for preterm PROM at earlier gestational age (22–27 weeks, 28–31 weeks, 32–33 weeks, and 34–36 weeks: 5.2 [2.3–11.8], 7.1 [3.4–15.0], 3.8 [1.7–8.3], and 3.9 [1.8–4.6], respectively). In cases, 171 underwent the prophylactic cervical cerclage. The occurrence of preterm birth and preterm PROM was comparable between those with and without the cerclage (28.7 versus 24.2, and 12.9 versus 13.3%, respectively). Conclusions: Pre-pregnancy excisional cervical surgery was associated with the increased risk of preterm birth, especially before 32 weeks of gestation. The prophylactic cerclage did not reduce the risk of preterm birth.
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