Noninvasive assessment of fetal anaemia

Abstract

In pregnancies complicated by severe red cell alloimmunization, fetal haemolytic anaemia can lead to intrauterine demise as early as 17 weeks' gestation. Intrauterine intraperitoneal blood transfusion, introduced by Liley in 1963, proved to be the first successful example of fetal therapy. The use of this complex procedure, involving X-ray guided puncture of the fetal peritoneal cavity, was limited to fetuses with a gestational age ranging from 24 to 33 weeks. When performed below 26 weeks, survival rates were as low as 16%. The need for intrauterine transfusion was mainly based on determination of bilirubin levels in amniotic fluid, and plotting the results in a three-zone chart devised by Liley. This chart was based on correlations of amniotic fluid bilirubin concentrations with the degree of neonatal anaemia, and ranged from 27 to 41 weeks' gestation. In the 1980s, with the introduction of ultrasound-guided intravascular transfusion, treatment became possible from 17–18 weeks' gestation onwards. Consequently, there was a need for diagnostic tests to assess the degree of anaemia in the second trimester fetus. The use of the Liley chart was shown to be unreliable in the prediction of disease severity before 27 weeks' gestation. Ultrasonographic detection of fetal hydrops in these pregnancies reliably indicates severe anaemia, but for reasons that are still unclear, a significant number of severely anaemic fetuses do not show ultrasonographic signs of hydrops. In 1988, Nicolaides et al studied the use of several ultrasonographic parameters to predict anaemia in nonhydropic fetuses. Their results were disappointing, and they concluded that the only reliable diagnostic test to assess the degree of fetal disease was fetal blood sampling.