Chorionic chromosome abnormalities and intrauterine growth retardation.

Chorion, placental membranes, and embryo all arise from the same fertilized oocyte; therefore, chorionic cells are presumed to reflect fetal chromosome status. Progenitor cells of the embryo are selected from the blastocyst, however, at a very early stage of development. If mitotic nondisjunction were to occur in one of the blastocyst cells destined to become trophoblast, the resultant abnormal cell line would be restricted to extraembryonic tissues. Indeed, chromosome mosaicism confined to the placenta has been found repeatedly in diagnostic chorionic villus sampling, and occasionally in third trimester placentas. Cytogenetically abnormal placental cells are morphologically and perhaps functionally abnormal. Such aberrations might result in deficient oxygen or nutrient supply to the fetus, causing intrauterine growth retardation (IUGR). To investigate this hypothesis we studied chorion and cord blood samples after delivery from 11 confirmed IUGR pregnancies. A minimum of 10 cells were analyzed from each cord blood and chorion specimen (mean number of cells from cord blood = 27; from chorion = 17). None of the cases showed true mosaicism for a hyperdiploid line. We conclude from this preliminary study that few, if any, cases of IUGR are likely to be due to chorionic mosaicism.