Fertility

The research, published Monday in the journal Occupational and Environmental Medicine, also found that working antisocial hours (in the evenings or night) or rotating shifts, may also impact female fertility.

Though the underlying cause is not known and more research is needed to further verify the findings, the team at the Harvard T.H. Chan School of Public Health believes that women in their reproductive years may need to consider this when trying to conceive.

The five-month-old boy has the usual DNA from his mum and dad, plus a tiny bit of genetic code from a donor.

US doctors took the unprecedented step to ensure the baby boy would be free of a genetic condition that his Jordanian mother carries in her genes.

Experts say the move heralds a new era in medicine and could help other families with rare genetic conditions.

But they warn that rigorous checks of this new and controversial technology, called mitochondrial donation, are needed.