Discouraging news for women over 30 who want to have a child comes from the UK. According to a study in the journal PLOS One, by the time a woman reaches 30, she has used up nearly 90% of her reserves of eggs. By the time she is 40, only 3% remains. Scientists at the University of St Andrews and Edinburgh in Scotland tracked the growth of the ovarian reserve from conception to 50. They found that the number of eggs declines far more rapidly than most women realise. "Our research shows that they are generally over-estimating their fertility prospects,” says Dr Hamish Wallace, one of the authors.

The study also dumps cold water on the intriguing theory that new eggs are produced in adults when germline stem cells in bone marrow reach the ovaries. Research on mice suggested that this might happen in humans, but the study is sceptical: “our model provides no supporting evidence of neo-oogenesis in normal human physiological ageing”. ~ London Telegraph, Jan 27; PLOS One, Jan 27