The Follicular Phase of the Menstrual Cycle

The Beginning of Your Period

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The follicular phase of your menstrual cycle, also known as the proliferative phase, begins on Day One of your cycle. Day One is, by definition, the day your period starts. This phase ends when a hormone called luteinizing hormone (LH) peaks and ovulation occurs, at which point you pass into the luteal phase of your cycle.

What Happens During the Follicular Phase?

In the early stages of the follicular phase, but after your menstrual flow has ended, the lining of the uterus is at its most thin, and your levels of estrogen and progesterone are at their lowest.

Later on in the follicular phase, proliferation (or thickening) of the uterine lining occurs. This thickened lining is preparing your body for a possible pregnancy.

The follicular phase typically lasts about 14 days, at which point the luteal phase begins.

What Implications Do the Follicular Phase, and the Follicles in General, Have on Your Fertility?

Follicle growth and development are regularly tracked during fertility treatments. During superovulation, used during in-vitro fertilization (IVF), the goal is to stimulate the ovaries to develop several mature follicles at once.

So what happens during the follicular phase that gets your follicles ready for possible pregnancy?

At around Day Five, of your cycle, increasing amounts of LH are released to help your follicles mature. As they do so, they begin to produce estrogen. Estrogen works to stimulate more LH production, which continues the maturation process of these follicles.

Around Day Eight of your cycle, one of these developing follicles emerges as the dominant one, and all of the others begin to shrivel and disintegrate.

Around the twelfth day, as mentioned above, the increasing level of estrogen causes the lining of your uterus to thicken as it prepares for the implantation of a fertilized egg.

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