Follicles usually begin to grow initially between days 6-14 of the menstrual cycle, during which time the primordial follicle in the ovary begins to grow and develop. The period of 8-10 days from the start of development is known as the follicular phase, during which only one good quality follicle emerges, which eventually grows into a mature follicle of 18mm or more, while the other follicles are inhibited from further development. The other follicles will be inhibited from further development. By the 16th day of a woman’s menstrual period, the mature follicle will be expelled, i.e., ovulation will occur. At this time, intercourse is easy to conceive, and it is very easy for a fertilized egg to be produced. So the follicular growth period of most women can be deduced from the timing of the menstrual period. The follicles usually start to develop after the menstrual period and grow at a rate of about 1-2mm per day, the closer they are to ovulation, the faster they grow.