The association between fetal karyotype and mean corpuscular volume.

To determine whether elevated fetal mean corpuscular volume is characteristic of a chromosome abnormality or fetal disease, 22 fetuses with chromosome abnormalities, 31 with uteroplacental insufficiency, 50 undergoing their first cordocentesis for hemolytic disease, and 50 control fetuses were identified. Chromosomally abnormal fetuses had a significantly higher mean corpuscular volume than the control fetuses. Among fetuses with chromosome abnormalities, the mean corpuscular volume for trisomic or triploid fetuses was significantly higher than for fetuses with other chromosome abnormalities. An elevated mean corpuscular volume was also associated with uteroplacental insufficiency, intrauterine growth retardation, and hemolytic disease. It correlated significantly with gestational age (p less than 0.002 in all cases) in all groups except trisomy or triploidy. In addition, it correlated with hematocrit in the hemolytic disease group (r = -0.60, p less than 0.0001) and with PO2 in fetuses with intrauterine growth retardation (r = -0.43, p = 0.005) from all causes including uteroplacental insufficiency. Trisomic or triploid fetuses showed no such relationships and therefore appear to have escaped the normal control mechanisms for erythropoiesis. One in 12 fetuses with an elevated mean corpuscular volume had trisomy or triploidy, whereas no fetus with trisomy or triploidy had a normal mean corpuscular volume. Thus an unexpectedly elevated fetal mean corpuscular volume in a patient undergoing cordocentesis for reasons other than evaluation of fetal chromosomes would appear to warrant further karyotypic analysis.