Doppler changes in umbilical artery, middle cerebral artery, cerebroplacental ratio and ductus venosus during open fetal microneurosurgery for intrauterine open spina bifida repair

Objective To describe changes in fetal Doppler parameters during a novel technique for open fetal microneurosurgery for open spina bifida (OSB) repair. Methods This was a prospective study of 44 fetuses undergoing open fetal surgery for OSB repair using a novel microneurosurgery approach that is characterized by a mini‐hysterotomy (diameter of 15 mm), minimal fetal manipulation and maintenance of a constant normal amniotic fluid volume throughout the procedure. Doppler velocimetry of the umbilical artery (UA), fetal middle cerebral artery (MCA) and ductus venosus (DV) was performed before the start of surgery and at prespecified timepoints during fetal surgery. UA pulsatility index (PI) > 95th percentile, DV‐PI > 95th percentile, MCA‐PI < 5th percentile and cerebroplacental ratio (CPR) < 5th percentile were considered abnormal. Results Median gestational age at fetal surgery was 25.2 weeks (range, 22.9–27.9 weeks). Doppler recordings were successfully obtained in all cases during all timepoints throughout the surgery. As compared with Doppler values before surgery, there was a significant increase in the proportion of fetuses with MCA‐PI < 5th percentile (63.6% vs 13.6%; P < 0.001), CPR < 5th percentile (65.9% vs 15.9%; P < 0.001) and DV‐PI > 95th percentile (22.7% vs 0%; P = 0.01) and a non‐significant increase in the proportion of fetuses with UA‐PI > 95th percentile (11.4% vs 0%; P = 0.12) during fetal surgery. None of the fetuses showed absent or reversed end‐diastolic velocity in the UA or absent or reversed DV a‐wave at any stage during OSB repair. All abnormal Doppler parameters returned to normal after surgery. Conclusions During open fetal surgery for OSB repair, a small hysterotomy, reduced fetal manipulation and maintenance of a normal amniotic fluid volume seem to prevent severe fetal Doppler abnormalities. The mild Doppler changes observed during fetal surgery could be a manifestation of fetal adaptation to the stress of fetal surgery.