Tests on blood taken from a pregnant woman can reveal which genes are switched on in the placenta. The finding paves the way for non-invasive, safer, pre-natal tests for a range of disorders, including Down’s syndrome and pre-eclampsia.

In blood samples from pregnant women, researchers isolated molecules produced only by genes in the placenta. The molecules, messenger RNA, give genetic information about the fetus, not the mother, because genetically the placenta is part of the baby.
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