Impact of general anesthesia with vasopressor support on uteroplacental perfusion during fetal spina bifida repair

OBJECTIVES: To evaluate the combined effect of maternal general anesthesia and vasopressor support on uterine hemodynamics during the second trimester in pregnancies undergoing fetal spina bifida repair and to determine whether fetal spina bifida repair alters uteroplacental perfusion. METHODS: This was a prospective single-center study conducted at the Fetal Medicine Unit of University Hospitals Leuven, Leuven, Belgium between August 2021 and April 2025. All participants underwent fetal spina bifida repair under general anesthesia with vasopressor support, titrated to maintain a mean arterial pressure ≥ 90% of the preoperative baseline value. Uterine artery (UtA) and umbilical artery Doppler measurements were obtained at six timepoints: (1) the day before surgery to establish preoperative baseline values; (2) immediately after epidural catheter placement, initiation of general anesthesia and intubation (at the initiation of noradrenaline); (3) 5 min after initiation of general anesthesia with vasopressor support; (4) at the end of surgery, after maternal skin closure and before extubation; (5) on postoperative day 1; and (6) on postoperative day 6. The primary outcome was the change in UtA pulsatility index (PI) 5 min after initiation of general anesthesia compared with the preoperative baseline value. Secondary outcomes included UtA blood flow estimated from time-averaged maximum velocity and vessel diameter and fetal umbilical artery Doppler parameters. Statistical analysis included paired t-tests, Wilcoxon signed-rank tests and mixed-effects models. RESULTS: A total of 33 women undergoing fetal spina bifida repair were included, of whom 23 underwent open repair and 10 underwent fetoscopic repair. At the preoperative baseline, median UtA-PI was 0.77 (interquartile range (IQR), 0.64-0.95), median UtA resistance index (RI) was 0.52 (IQR, 0.45-0.59) and median UtA blood flow was 307.5 (IQR, 209.8-542.2) mL/min. At 5 min after the initiation of general anesthesia with vasopressor support, UtA-PI (median, 0.87 (IQR, 0.68-1.04)) and UtA blood flow (median, 310.7 (IQR, 199.0-421.4) mL/min) were comparable to baseline values (both P > 0.05). At this timepoint, umbilical artery PI was higher than the baseline value (P = 0.008) while fetal heart rate decreased. At the end of surgery, UtA-PI (median, 1.46 (IQR, 1.04-2.21)) and UtA-RI (median, 0.76 (IQR, 0.62-0.91)) were elevated compared with baseline values (both P < 0.001) and UtA blood flow was reduced (median, 182.1 (IQR, 79.8-351.5) mL/min; P = 0.031). Elevation of UtA-PI and UtA-RI persisted on postoperative days 1 and 6, but umbilical artery indices generally normalized back to preoperative baseline levels. There were no significant differences in UtA or fetal Doppler parameters between surgical techniques. CONCLUSIONS: General anesthesia with vasopressor support preserved uterine perfusion and blood flow without increasing vascular resistance. During fetal spina bifida repair, UtA resistance increased and UtA blood flow decreased. These parameters did not normalize back to preoperative baseline values within 6 days after surgery. In contrast, perioperative fetal Doppler changes resolved immediately postoperatively © 2026 International Society of Ultrasound in Obstetrics and Gynecology.