Middle cerebral artery velocimetry as a predictor of hypoxemia in fetuses with increased resistance to blood flow in the umbilical artery.

About half of all fetuses with increased resistance to blood flow, but with still detectable diastolic blood velocity in the umbilical artery (UA), show signs of imminent asphyxia during labour indicating a need for operative delivery. Fetal brain-sparing during hypoxia is characterized by an increase in diastolic and mean blood flow velocity in the middle cerebral artery (MCA). The aim of this study was to assess whether MCA blood velocity in pregnancies with increased resistance to blood flow in the feto-placental circulation could predict the development of fetal asphyxia during labour. Fifty pregnant women with signs of increased feto-placental vascular resistance between 31 and 42 weeks of gestation were studied serially by Doppler ultrasound and the last examination was correlated to perinatal outcome. The MCA pulsatility index (PI), cerebroplacental PI ratio and mean MCA blood velocity were calculated and correlated to fetal outcome. Fetal brain-sparing was defined as MCA PI < mean -2 S.D., cerebroplacental PI ratio < 1.08 and mean MCA blood velocity >mean + 2 S.D. No significant association was found between signs of fetal brain-sparing and the perinatal outcome. Among fetuses with signs of increased resistance to flow in the umbilical artery, velocimetry of the middle cerebral artery did not identify those that would not withstand the strain of labour.