Poor uterine contractility and postpartum hemorrhage among low-risk women: A case-control study of a large-scale database from Japan.

Objective: To examine the association between the risk of postpartum hemorrhage (PPH) and poor uterine contractility, which is suggested by the characteristics of labor.

Methods: This case-control study used cases recorded in the Japan Perinatal Registry database during the period 2013-2016. After exclusion of women with specified known risk factors for PPH, we enrolled 174 082 primiparas who had a full-term live singleton vaginal birth. Participants were classified into four classes according to the diagnosis of abnormal labor patterns and use of uterotonics. χ tests were used to compare PPH cases with controls, and odds ratios (OR) were calculated by univariate and multivariate analyses.

Results: Among the enrolled women, 10 508 (6.0%) had PPH. Abnormal labor patterns were significantly associated with an increased risk of PPH. Compared with women without any abnormal labor patterns who had not used uterotonics, women with abnormal labor patterns were at a significantly increased risk for PPH regardless of whether they had used uterotonics (adjusted OR 1.23, 95% confidence interval [CI] 1.10-1.37) or not (adjusted OR 1.30, 95% CI 1.23-1.37).

Conclusion: Our study suggests that among low-risk women with PPH, poor uterine contractility in labor could be a significant predisposing risk factor for PPH.