The sperm carrying the X chromosome (female) is slightly larger than the sperm carrying the Y chromosome (male).
While the difference in size is minute, it does impact the speed of the sperm. Y-chromosome sperm are faster, but X-chromosome sperm live longer. This is because X-chromosome sperm are slightly larger and therefore have more resources.
The size difference is not significant enough to determine the sex of a baby. The sex of a baby is determined by the chromosome in the sperm that fertilizes the egg. If the sperm carries an X chromosome, the baby will be female. If the sperm carries a Y chromosome, the baby will be male.
