Cohort study of the incidence of spontaneous preterm birth and septic abortion referred by pathological examination in Gifu prefecture in Japan.

Aims: To clarify the incidence of spontaneous preterm birth (PB) and septic abortion (sab) in Gifu prefecture in Japan.

Study Design: This prospective, population-based cohort study was approved by our hospital's Institutional Review Board. All 36 hospitals (100%) in Gifu prefecture offering obstetrical services participated in the study. Patient enrollment criteria were: sab and PB from 22 to <37weeks gestation (WG), excluding for maternal and fetal indications. Pathological examinations before 36 WG and associated factors for both PB and chorioamnionitis (CAM) stage 3 were analyzed by multiple logistic regression analysis judging from minimum daily clinical information in Gifu prefecture.

Results: The sab rate per all deliveries was 29/16871 (0.17%) at 16.9±2.9 WG. The total spontaneous PB rate was 615/16871 (3.65%) at 34.5±2.7 WG, with birth weight (BW) 2267±557g. There were 26 (0.15%) PBs from 22+0 to 27+6 WG (weeks+days) at 25.2±1.5 WG, with BW 745±199g. Among 214 pathological examinations, CAM was detected in 80% (sab) and 63% (PB<36 WG), respectively. Funisitis were 14% and 17% respectively. Episodes of serial genital bleeding and/or hematoma at <12 WG were more frequent in sab and earlier PB (<28 WG) associated with CAM stage 3 (odds 1.9, P<0.0001). Combined factors such as bleeding and past history of CAM correlated with earlier delivery at 23.4±5.9 WG (P=0.0032).

Conclusion: In Gifu prefecture, the incidence of sab was 0.17% (per all deliveries) and 3.65% of spontaneous PB. The combined risk of past CAM history and bleeding was associated with earlier delivery among total preterm birth.