Medical researchers in Britain say they have found an unexpected risk in test-tube baby techniques.

They have discovered a case in which two embryos, one male and one female, fused in development to form a single child.

The case, outlined in the New England Journal of Medicine, surfaced when an otherwise healthy child was treated because his left testicle had not descended normally.

Unexpected risk in test-tube baby techniques

Surgeons discovered an ovary and a fallopian tube on the left side.

In medical terms the child is known as a chimera, after the Greek monster that was part lion, part goat and part serpent.

Researchers at the University of Edinburgh in Scotland think that the standard practice of implanting more than one embryo in the womb during in vitro fertilisation (IVF) made it possible for the two embryos to fuse.

Chimerism can happen naturally but it is so rare that the researchers think this case suggests that IVF makes it more likely.

The risk of chimerism has risen in recent years because more women are taking fertility drugs which release multiple eggs for fertilisation.

In IVF doctors routinely put back more than one embryo into the womb to improve the chances of a successful pregnancy, which increases the risk of chimerism even further.

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