Fetal cerebral blood flow redistribution in late gestation: identificationof compromise in small fetuses with normal umbilical artery Doppler

Objective To evaluate the role of middle cerebral artery Doppler in small f etuses during the late third trimester. Design Prospective observational study of structurally normal fetuses with an estimated fetal weight < 5th percentile for gestation. Perinatal outcome was determined using a structured datasheet sent to each referring obstetr ician. Subjects Structurally normal fetuses at 35 or more weeks of gestation refer red during a 2-year period to the fetal growth clinic of a regional fetal m edicine unit in North London. Fetuses with aneuploidy and/or major structur al abnormalities were excluded. Methods Umbilical artery and middle cerebral artery (MCA) Doppler waveforms were recorded and considered abnormal if above 95th or below 5th percentil es, respectively. Amniotic fluid was considered reduced if the maximum vert ical cord-free pool was < 2 cm. The placenta was considered mature if the G rannum grade was II or III. The head circumference (HC)/abdominal circumfer ence (AC) ratio was considered abnormal if > 95th percentile for gestation. Fetal growth, amniotic fluid, biophysical profile score and umbilical arte ry Doppler were used to advise the referring obstetrician about fetal well- being and he/she independently decided both the timing and mode of delivery . Results Forty-seven fetuses fulfilled the entry criteria. Thirty-four (72%) demonstrated normal umbilical artery Doppler waveforms. Sixteen (34%) demo nstrated middle cerebral artery redistribution, of which nine (56%) had nor mal umbilical artery Doppler waveforms. MCA blood flow redistribution was a ssociated with an increased incidence of cesarean delivery and need for neo natal admission. Of all gray-scale parameters, an elevated HC/ AC ratio has the strongest association with MCA blood flow redistribution (15/16 vs. 1/ 31; P < 0.01). Conclusions MCA Doppler may be a useful tool to assess the health of small fetuses in the late third trimester. Redistribution may occur in the presen ce of normal umbilical artery Doppler and should be suspected when the HC/A C ratio is elevated.