Abnormal immunological development in fetuses with trisomy 18

Flow cytometry was used to enumerate the lymphocyte subpopulations in fetal blood obtained by cordocentesis from eight trisomy 18 fetuses at 20–36 weeks' gestation. Compared with values in chromosomally normal fetuses, in trisomy 18 the mean T- and natural killer (NK) cell counts were significantly lower (t= ? 7·63, P<0·001 and t= ? 3·58, P<0·01, respectively); the mean B-cell count was not significantly different (t= ? 1·32). These findings demonstrate that in trisomy 18 there is abnormal intrauterine development of the immune system.