Longitudinal measurement of peak systolic velocity in the fetal middle cerebral artery for monitoring pregnancies complicated by red cell alloimmunisation: a prospective multicentre trial with intention-to-treat.

OBJECTIVE: To evaluate the utilisation measurements of peak systolic velocities in the middle cerebral artery combined with B-mode ultrasound imaging to predict anaemia in an unselected population of pregnancies complicated by alloimmune antibodies known to cause immunological hydrops.
DESIGN: Prospective study on an intention-to-treat basis.
SETTING: Multicentre study in five large tertiary referral centres. POPULATION: One hundred twenty-five fetuses with maternal alloantibodies known to cause immunological hydrops.
METHODS: If peak systolic velocity and B-mode scan were reassuring the pregnancy was monitored at 7-14 days interval. If either method showed signs of anaemia, an umbilical fetal blood sampling was performed. When the gestational age was greater than 35 weeks, labour was induced. MAIN OUTCOME MEASURE: Moderate to severe anaemia at delivery.
RESULTS: Overall sensitivity to detect moderate to severe anaemia below 35 weeks (haemoglobin level below 0.65 multiples of median) was 88%. Specificity was 87%; positive predictive value was 53% and negative predictive value was 98%. The diagnosis of severe anaemia was missed in one fetus; however, the final outcome was good. The method was not useful after 35 weeks.
CONCLUSIONS: Middle cerebral artery peak systolic velocity is a highly sensitive non-invasive means for determining the degree of anaemia present in red blood cell alloimmunised pregnancies. The widespread use of the Doppler method will minimise fetal complications associated with amniocentesis and fetal blood sampling. Non-invasive measurement of middle cerebral artery peak systolic velocities is more convenient and acceptable to alloimmunised pregnancies and may significantly lower health care costs. A Doppler interval of seven days is recommended.