Since the birth of the triplets in 1997, the couple, from Thrybergh in South Yorkshire, have had a fourth child, conceived naturally and unexpectedly.

BBC: Triplets mother wins IVF case

In a study of more than 13, 000 UK children, five-years-olds were about twice as likely to have asthma if they were not conceived naturally.

BBC: Fertility treatment 'asthma link'

Preston, who hasn't said whether she conceived naturally or with the help of donor eggs or any other form of technology, joins a list of celebrities who became pregnant in their mid- to late 40s.

CNN: Pregnant at 47: Can I do that?

However, Jacques Donnez and his colleagues at the Catholic University of Louvain, in Belgium, have gone one better, with news that they have overcome this hurdle, and that one of their cancer patients who received an ovarian graft has conceived naturally and is expecting a child at the end of September.

ECONOMIST: Frozen ovaries could help women to stay fertile

There is evidence, however, that IVF babies are at greater risk of birth defects than naturally conceived babies.

BBC: What is society's problem with elderly mothers?