Follicular Phase–The days immediately post menstruation till ovulation is considered follicular phase when few follicles grow every cycle in the ovary . One of these follicle becomes the dominant follicle and outgrows other follicles .
LH surge 36 hours prior to ovulation there surge in the LH levels leading to dominant follicle releasing the egg from the dominant follicle which is called ovulation. Egg survives in birth canal for 24 hours and should meet the sperm during this period for fertilisation to take place .
Luteal Phase – Following ovulation the ovary produces progesterone under influence of which necessary changes take place in the endometrium which favours implantation. During luteal phase progesterone level is increased in blood which continues to be high if pregnancy takes place. In the absence of pregnancy the progesterone level falls leading to shedding of endometrium which comes out of vaginal track in the form of menstrual blood .