The follicular phase is part of a woman's monthly cycle. It begins on the first day the menstrual period starts and ends as soon as ovulation occurs. There is no set length of time that the follicular phase lasts. Every woman's cycle is different, and the length of this phase can vary by a great number of days. Some women may have a follicular phase that lasts for just a week, while for others it might last for several weeks. After this phase ends, ovulation and the luteal phase normally follow before the cycle starts all over again the next month.
During the follicular phase and just as the menstrual period begins, levels of estrogen and progesterone hormones are at their lowest points. A woman's body will release the FSH, or follicle stimulating hormone, at this time to give the ovarian follicles the signal that it is time to start maturing new eggs. One follicle is typically dominant over the others, and the egg inside it is the one that is released. When this happens, the follicular phase has officially ended and ovulation has begun. Ovulation is considered to be the best time of the month for the average woman to get pregnant, but pregnancy can also occur during the follicular and luteal phases.
The onset of ovulation varies among women, but for most it occurs between days 12 and 14 of the monthly cycle. Many women can determine exactly when ovulation is happening by using a calendar and noting the start and end days of their periods. After the period has ended, a woman might start experiencing symptoms of ovulation, such as an increase in body temperature and changes in the consistency of her cervical mucus. The day that ovulation begins is also considered day one of the luteal phase.
In most cases, the luteal phase of the average woman will last for the same number of days each month. Tracking it on a calendar for a few months can give a woman a good idea of how long it lasts and exactly when she should expect her period to arrive. For most women, the length of the luteal phase is 14 to 16 days. The last day of the luteal phase is considered to be the last day before the menstrual period begins. On the first day that a woman's period starts, the entire cycle begins again with the follicular phase.