The surgery was designed to place the fetal cells precisely.

But the use of fetal cells was not all that made the experiment controversial.

This would avoid the ethical problems in using fetal cells.

"So a few fetal cells find their way into the mother's blood."

Did clinical improvements have anything at all to do with growth of the fetal cells?

The fetal cell was still in place under the outer skin of the egg.

In some patients, the fetal cells apparently grew too well.

One obstacle is that very few fetal cells survive, even in animals.

Experts said the new study showed that fetal cells can indeed be found in the blood of pregnant women.

These and other mutations can be identified through studies of fetal cells.