More than 1 million babies have been born with the help of in-vitro fertilization.

But some IVF research is under fire, after Norbert Gleicher, a leader in the IVF industry, told a scientific meeting that he had transplanted male cells into three-day old female embryos.

"The basic experiment was to see can one transplant from one embryo to another," Gleicher said.

Gleicher said the experiment showed that cells from a sibling could be transplanted into an embryo to prevent certain genetic diseases.

"So the purpose of our experiment was not to create a mixture of female or male embryo, that was just a tool to answer the question, whether the transplant worked," Gleicher said.

But the experiment has been criticized by some scientists and ethicists.

"I don't know whether Gleicher's research was unethical or not; I'm not saying that. But I am saying that if it was possible to do the experiment in other ways, then it was unwise and unnecessary for the scientist to make a hybrid embryo, part male, part female," said Thomas Murray of Hastings Center for Bioethics.

Murray said that this may have increased public mistrust in science.

"People are frightened enough about what goes on. The scientific laboratories should not have something unnecessary like that to further make them mistrustful of science," Murray said.

Gleicher disagrees and said the research could lead to progress in curing many single gene diseases.

The IVF industry is self-regulated because it does not receive any government funding. For more information, visit www.sciencentral.com.