A new chemical treatment that can segregate male and female spermcould one day mean parents going through IVF could choose whether they have a boy or girl. 

Scientists discovered the sperm with the X chromosome (which gives rise to females) slowed down when when a certain chemical was added while sperm with the (male) Y chromosome sped up. 

In experiments with mice sperm, scientists found they could produce litters that were 90 per cent male, according to the study published in Plos Biology. When the slower sperm were used, litters were 81 per cent female.