There are two kinds of sperms – the male one that embodies Y chromosome and the female one having X chromosome. The male sperm are known to be fast, but weak, whereas the female one is slower but more pliant. As such, this method is based on the timing and perceiving when you are ovulating. To enhance possibility of conceiving girl child, you need to have sex two to three days prior ovulation because female sperms are more existing power. To better chances of having boy, have sex as near ovulation as possible.