He was a bright baby, though much more challenging then any of my other children, and well ahead of the developmental curve for many things, crawled early, walked early, began to talk early, but then about 14 months began to regress.

FORBES: Look Out For An Increase In Autism

Mr Albert also stresses that the reasons why teenagers get pregnant and carry a baby to term are much more complicated than the content of sex education lessons - and notes that many young people take no notice of what they are taught at school.

BBC: NEWS | Americas | Chastity pressed on US teens

Although the reason is not yet understood, earlier studies have shown that finger-length ratios are a robust marker of how much of that hormone a baby has been exposed to in utero the more testosterone, the longer the ring finger.

ECONOMIST: Autism