in human females, what happens when
(i) egg is fertilized
(ii) the egg is not fertilized

(i)

If the egg is fertilized, the egg creates a barrier so that no other sperm can get in. At the instant of fertilization, your baby's genes and sex are set.During fertilization, the haploid nucleus of the sperm and ovum fuse to form a zygote. This zygote divides to form an embryo. It keeps dividing as it moves slowly through the fallopian tube to the uterus. Its next job is to attach to the lining of uterus. This is called implantation. Here, the zygote divides to form an embryo, which develops into a foetus. Food is provided to the feotus by placenta.This leads to pregnancy and new baby is born.

(ii)

If the egg is not fertilized, the inner lining of the uterus (endometrium) which is chiefly maintained for the implantation of fertilized egg gets degenerated and discharged from the uterus as menstrual bleeding.
This process is called menstruation.

In short we can say that, if egg is fertilized it leads to pregnancy and if the egg is not fertilized it leads to menstruation.