Follicular Phase

Definition - What does Follicular Phase mean?

The follicular phase of the menstrual cycle begins with the first day of menstruation, at which time the body begins preparing a new batch of follicles to produce a mature egg. It ends with ovulation when the mature egg is released to the fallopian tube where it may be fertilized by sperm. The last few days of the follicular phase, plus the ensuing ovulation, comprise the most fertile time in a woman's cycle.

The follicular phase may also be referred to as the proliferative phase.

FertilitySmarts explains Follicular Phase

During menstruation, the pituitary gland in the brain begins to release a hormone called follicle-stimulating hormone (FSH). This hormone triggers the ovaries and uterus to begin preparing for possible conception in several ways:

  • Within the ovaries, ovarian follicles begin to prepare to release an egg into the uterus.
  • The cervix starts to produce cervical mucus to assist sperm in entering the uterus.
  • Uterine lining thickens to prepare for possible pregnancy

Under the influence of FSH, five or more ovarian follicles begin to mature. Each follicle nurtures an egg cell, as well as producing other hormones that assist in driving the reproductive cycle.

Though several follicles begin the maturation process, in most cases only one follicle will emerge as "dominant" and release a mature egg. In rare cases, two or more mature eggs might be released, leading to the conception of fraternal twins or triplets. The ovaries may also be artificially induced to bring multiple eggs to maturation at once through the administration of hormones, as in preparation for in vitro fertilization (IVF).

The follicular phase is the part of the menstrual cycle that varies most from woman to woman. In some women, the process of egg maturation may take only a few days. In others, this process may take over two weeks. For an average woman with a menstrual cycle of 28 days, ovulation occurs around day 14 of the cycle.

A woman can learn on what day she ovulates by observing her body across multiple menstrual periods. Generally, the hormones that cause ovulation also cause a rise in body temperature when they are released. Cervical mucus also peaks immediately before ovulation, and the position of the cervix may shift as the body prepares for possible pregnancy. Urine tests for luteinizing hormone (LH) are also available, which may provide an additional indicator of whether ovulation is near.

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