Prenatal diagnosis: a problem in verification.

Prenatal cytogenetic diagnosis based on cultured amniotic fluid cells demand confirmation from other fetal tissues in the event of pregnancy termination. Various fetal tissues, including cord blood, have been utilized for such cytogenetic confirmation. We wish to report a hazard which may be encountered in the use of fetal blood for such verification. Partial trisomy 15 (Fig. la) was diagnosed by amniocentesis during the 16th week of the fourth pregnancy of a mother known to carry a balanced 4/15 translocation (Fig. lb). The proposita of this family was a severely retarded 4 year old with partial trisomy 15 (to be reported in detail elsewhere). As a result of the cytogenetic findings, termination of pregnancy, 23 days later (19 weeks' gestation), was induced by hypertonic urea. A macerated fetus (histologically confirmed) was delivered 18 hours following the infusion. The placenta was not expelled spontaneously and was removed manually. Culture of the following fetal tissues was attempted: cord blood obtained at the bifurcation of the umbilical vein on the chorionic plate; fetal side of the placenta; amnion; skin; lung, and intestine. The only successful cultures were derived from cord blood and placenta. In 30 metaphases analysed from cord blood, all had a karyotype identical to that of the carrier mother 46,XX,t(4p+;15q-). No metaphases of 47,XX, + (15q -), as seen in all cells of the amniotic fluid culture, were observed. However, chromosome analysis of fetal placenta revealed only cells with the partially trisomic karyotype (Table I). Histological examination of the placenta revealed subchorionic necrosis with typical villi which, in some areas, appeared structurally normal with a covering of syncitium and a few cytotrophoblastic