A 37-year-old, primigravid woman underwent amniocentesis at 16 weeks of gestation because of bilateral pleural effusion in the fetus and a high risk (1:31) result of trisomy 21 determined by second-trimester maternal serum screening. Prenatal ultrasound at 15 weeks of gestation showed bilateral pleural effusion, arrhythmia and hydrops fetalis. Using the DNA extracted from uncultured amniocytes by the application of quantitative fluorescent polymerase chain reaction (QF-PCR) and the informative polymorphic DNA markers of D21S1437, D21S2052 and D21S2054, a diagnosis of trisomy 21 was made ( Fig. 1 ). Simultaneous cytogenetic analysis of cultured amniocytes revealed the result of 47,XY,+21 ( Fig. 2 ). The parental karyotypes were normal. The pregnancy was subsequently terminated, and a malformed hydropic fetus was delivered. QF-PCR analysis on the DNA extracted from umbilical cord, placenta and parental bloods showed a maternal origin of the trisomy 21, consistent with maternal meiosis I non-disjunction ( Fig. 1 ).
