The incidence of PPH was compared among the three historical cohorts who received different oxytocin regimens (10 IU IM, group A; 5 IU IV, group B; and 10 IU IV, group C) following propensity score matching for those variables that proved to be significantly associated with PPH.<h4>Results</h4>During the study period, 3850 women had a vaginal birth at our tertiary care unit (1245 in the 10 IU IM group, 1291 in the 5 IU IV group and 1314 in the 10 IU IV group) and were enrolled in the study population. This evidence concerns the gene OXT and pulmonary arterial hypertension.