Dr Allan Pacey, senior lecturer at the University of Sheffield and secretary of the British Fertility Society, said some studies had shown an increased risk associated with some assisted reproductive techniques .

BBC: IVF 'not reason for birth risks'

Scientific studies have shown that human fertility starts declining at the age of 31, which is the age many women are having their first babies.

BBC: The cost of fertility treatment 'tourism'

Studies showed that during periods of high fertility, women are more drawn to more rugged, dominant-looking men.

CNN: Beholding beauty: How it's been studied