Risk Factors of Preterm Birth in Okinawa Prefecture, the Southernmost Island Prefecture of Japan.

OBJECTIVES: A high rate of preterm birth has been reported in Okinawa Prefecture, the southernmost island prefecture of Japan. Hence, this study aimed to identify the risk factors for preterm birth in this prefecture. METHODS: This retrospective study included data from January 2013 to December 2019 from three facilities in Okinawa Prefecture. Of 13,468 cases of preterm birth at ≥ 22 weeks of gestation, 11,868 were included in this study. Stillbirth and multiparity cases were excluded. First, we compared the overall preterm and full-term birth groups by categorizing the patient background, obstetric, and fetal risk factors. Further, we categorized preterm births into three groups (22-27, 28-33, and 34-36 weeks of gestation) and examined patient background factors to identify potential risk factors for the occurrence of preterm birth in each group. RESULTS: Preterm births accounted for 21.2% (2,521 cases) of all cases, with the rates of 2.6% (317 cases), 6.7% (800 cases), and 11.8% (1,404 cases) at 22-27, 28-33, and 34-36 weeks of gestation, respectively. To prevent preterm birth in Okinawa Prefecture, the present study specifically focused on patient background characteristics. In the multinomial logistic regression, the risk factors for preterm birth at 22-27 weeks of gestation were previous preterm birth (P < 0.0001) and lower age (P = 0.026); at 28-33 weeks of gestation, the risk factors were previous preterm birth (P < 0.0001) and history of cervical conization (P = 0.009); and at 34-36 weeks of gestation, only previous preterm birth (P < 0.0001) was a risk factor. CONCLUSIONS FOR PRACTICE: Previous preterm birth, younger age, and history of cervical conization were risk factors for Preterm birth in Okinawa. To reduce premature births in Okinawa Prefecture, it is important to pick up women with these risk factors and provide them with appropriate guidance and education on an ongoing basis.