Objective: To evaluate if moderate-severe endometriosis impairs uterine arteries pulsatility index (UtA-PI) during pregnancy when compared to unaffected controls. Design: Observational prospective cohort study. Setting: University-affiliated obstetrics and fetal medicine Department in Italy. Population: Pregnant women with stage III-IV endometriosis according to revised American Fertility Society (r-AFS) classification, matched in a 1:2 ratio according with body mass index and parity with unaffected controls. Methods: UtA-PIs were assessed at 11–14, 19–22 and 26–34 weeks of gestation following major reference guidelines. A General Linear Model (GLM) was implemented to evaluate the association between endometriosis and UtA-PI Z-scores. Main Outcome Measure: UtA-PI Z-scores, calculated from published reference equations of previously validated normal range. Results: Significantly higher third trimester UtA-PI Z-scores were observed in patients with r-AFS stage III-IV endometriosis when compared to controls (p=0.024). In the GLM, endometriosis (p=0.026) and maternal age (p=0.007) were associated with increased third trimester UtA-PI Z-scores, whereas conception by in-vitro fertilization with frozen-thawed embryo transfer significantly decreased UtA-PI measures (p=0.011). No differences were observed in first or in second trimester UtA-PI Z-scores of cases vs. controls. Conclusions: Stage III-IV endometriosis according to r-AFS classification is associated with a clinically measurable impaired placental perfusion as shown by increased UtA-PI Z-scores in the third, but not in the first or second trimesters. Closer follow-up may be recommended in pregnant patients affected by moderate-severe endometriosis in order to attempt prediction and prevention of adverse pregnancy/perinatal outcomes due to a defective late placental perfusion. Funding: N/A.