SURPRISINGLY large amounts of fetal DNA circulate in maternal blood.
Researchers looked for pieces of the Y chromosome鈥攚hich only men
possess鈥攊n 27 women who were carrying a male child. Early in their
pregnancy, an average of 3.4 per cent of the DNA in their blood plasma was
fetal. It could be detected as early as the 7th week of gestation鈥攁bout
two months before amniocentesis is possible.
The DNA doesn鈥檛 seem to come from intact fetal cells; these are more than 10
000 times less abundant than maternal cells in blood. More detailed genetic
analysis of the free-floating DNA could provide rapid diagnosis for genetic
abnormalities in the fetus (American Journal of Human Genetics, vol 62,
p 768).
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