Platelet count in normal, small, and anemic fetuses.

A reference range for fetal platelet count with gestation was established from the study of samples obtained by cordocentesis from 229 pregnancies that had prenatal diagnosis. The mean platelet count increased from 187 +/- 47 x 10(9)/L at 15 weeks to 274 +/- 47 x 10(9)/L at 40 weeks' gestation. In 113 red cell-isoimmunized pregnancies, the moderately anemic fetuses were significantly thrombocythenic, whereas the severely anemic fetuses were thrombocytopenic. In 136 small-for-gestational-age fetuses the platelet count was reduced and there were significant correlations between the magnitude of the thrombocytopenia and the degree of fetal smallness, hypoxemia, and acidemia.