But although the technique is ideal for enabling natural childbirth, it can also be adapted for women who know they are going to have complications.

BBC: 'Why I chose hypnobirthing'

Professor Leridon said the study had been carried out because it was important to answer a range of practical questions about the chances of either natural or artificially aided conception so that couples could be given more precise information about the potential risks of postponing childbirth beyond a given age.

BBC: The researchers evaluated women's chances of conceiving