A technique for detecting abnormalities in embryos may have been giving misleading results, according to papers presented at a Montreal conference of US and Canadian fertility doctors. In pre- implantation genetic diagnosis (PGD) one cell from an eight-cell embryo is extracted and examined for abnormalities. If an embryo appears to be healthy, it is implanted in the mother's womb. If not, it is usually discarded. Children born after the technique appear to be healthy, although there are no long-term studies.

However, it now appears that defective embryos are able to correct defects as they mature. One American experiment discovered that about half of the cells in "defective" embryos were normal by the blastocyst stage. This suggested two things to the fertility specialists. First, that defective embryos might be a viable source of embryonic stem cells, and second, that many embryos discarded as defective could have developed into healthy babies.

One initiative to emerge from the meeting is a US database to track the safety of PGD. American clinics are not presently required to report their data.