By Caroline Ryan
BBC News Online health staff in Berlin
Hypnosis can double the success of IVF treatment, researchers have claimed.
A team from Soroka University, Israel, found 28% of women in the group who were hypnotised became pregnant, compared with 14% of those who were not.
The study of 185 women was presented to the European Society of Human Reproduction and Embryology conference in Berlin.
But other experts said the research failed to account for key differences between the two groups.
The longer a couple have been trying to conceive, the less likely they are to conceive
Dr Francoise Shenfield
The Israeli researchers were looking to see if hypnosis could make the embryo transfer stage of IVF more successful.
During this stage, the embryo is transferred into the womb. However, if the womb is contracting, it can affect the chances of the transplant being a success.
It was hoped hypnotherapy could help women relax and therefore improve the chances of success.
Women undergoing IVF were assessed to see if they were suitable to be hypnotised.
Eighty-nine women were then given hypnosis while their embryos were implanted. Some underwent more than one cycle of IVF treatment.
Ninety-six other women underwent embryo transfers without hypnosis. All received one cycle each.
Dr Eliahu Levitas, who led the research, told the conference: "Embryo transfer is known to be a stressful time for patients, and it may be that the procedure is the peak of their stress in IVF.
"Hypnosis may be related to a tranquilising effect.
"Performing embryo transfer under hypnosis may significantly contribute to an increased clinical pregnancy rate."
But experts said the study failed to take into account key differences between the groups which would have a major influence on their chances of conceiving.
On average, women in the non-hypnosis group had been trying to conceive for 7.4 years, compared with 4.7 years for those who did receive hypnosis.
Dr Francois Shenfield, of University College London Hospital, UK, said: "One of the very important confounding factors in this field is the duration of infertility.
"The longer a couple have been trying to conceive, the less likely they are to conceive spontaneously, and with technical help."