A new study challenges the long-held belief that the sex of a child is solely determined by the sperm's X or Y chromosome. Researchers suggest that a woman's age may also play a significant role in influencing the likelihood of conceiving a boy or a girl. This finding indicates the sex ratio at birth is not a simple 50/50 split, as previously assumed. Further research is needed to understand the exact mechanisms behind this age-related influence and its implications for family planning and population demographics.