Making women laugh by "medical clowning" has been found to boost the chances of success during fertility treatment, in a study that appears to prove the therapeutic powers of humour.

Doctors in Israel have literally sent in the clowns to try to increase the chances of successfully transferring IVF embryos into the wombs of women undergoing fertility treatment.

Using a professionally trained clown to make 93 women laugh after the stressful operation of embryo transfer, the scientists found that the rate of successful pregnancies increased from 20 per cent to 35 per cent.

"A specially devised medical clowning session of 10 to 15 minutes was composed by our clown team. Women after embryo transfer lie for an hour in bed and the clown has a session with them," said Shevach Friedler of the Assaf Harofeh Medical Centre in Zerifin, Israel. "The clown approaches the bed where the woman is lying and he makes contact first by eye, then with conversation. The point is to get the women to smile and laugh. They use magic tricks and tell some jokes," Dr Friedler said.

One of the medical team, Shlomi Algussi, is a trained clown who dresses up in a chef's hat and a yellow and white vest."It makes them laugh and feel less anxious. After embryo transfer, stress could be critical," Dr Friedler said.