Healthcare provider with anatomical diagram explaining what follicular phase is

What Is Follicular Phase?

Written on November 25, 2023 by Sendra Yang, PharmD, MBA. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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A female is born with millions of eggs at birth.[1] Over her lifetime, only a select few eggs fully mature. The process of an egg maturing is part of the menstrual cycle. You may have wondered what is the follicular phase. During the menstrual cycle, the follicular phase is the stage where eggs undergo development. The menstrual cycle includes two additional phases: the ovulatory and luteal phases.[2] Continue reading to learn more about the three different phases of the menstrual cycle.

The Menstrual Cycle

The menstrual cycle starts on the first day of menstruation or bleeding, which is the shedding of the uterus lining.[2] A menstrual cycle lasts anywhere from 24 to 38 days and prepares a woman’s body for potential pregnancy. Up to 15% of women have cycles that last 28 days, while at least 20% have irregular cycles. Irregular menstrual cycles can be longer or shorter than the normal range.

Four main hormones regulate the menstrual cycle. Luteinizing and follicle-stimulating hormones promote ovulation and stimulate the ovaries to produce two more hormones: progesterone and estrogen.[2,3] Estrogen and progesterone prepare the uterus and breasts for potential fertilization. The hormone levels change throughout the different phases menstrual cycle and can cause various menstrual symptoms.

Follicular, Ovulatory, and Luteal Phases

The menstrual cycle has three phases: follicular, ovulatory, and luteal.[2,3] The follicular phase occurs before the egg is released and involves developing the egg to maturity.[1,2] Ovulation starts with an increase in luteinizing hormone and follicle-stimulating hormone and ensues when the egg is released about 16 to 32 hours after the hormone increase. The egg can be fertilized for around 12 hours after its release.

The luteal phase begins after ovulation and occurs after the egg is released. The luteal phase lasts approximately 14 days and ends before the next menstrual period. In this phase, the increased estrogen and progesterone help to prepare the body for potential pregnancies. If the egg does not get fertilized or if the fertilized egg does not implant, a new menstrual cycle starts. If the fertilized egg is properly implanted, a hormone called human chorionic gonadotropin is produced and is detected in pregnancy tests.

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More about the Follicular Phase

The follicular phase is also known as the proliferative phase.[4] During the follicular phase of the menstrual cycle, the egg matures in the ovaries.[1,4] The follicular phase ranges from 14 to 21 days. The duration of the follicular phase is dependent on the time it takes the dominant follicle to form a mature egg. Having intercourse in the five days preceding and on the day of ovulation results in the greatest chance of becoming pregnant.

A long follicular phase usually means that the menstrual cycle is also longer.[1,4] The follicular phase can be extended for a few reasons, such as taking birth control or having a vitamin D deficiency. There is also a possibility of having a shorter follicular phase. A short follicular phase could potentially indicate issues with conceiving. It’s expected that when a woman approaches menopause, the follicular phase will usually get shorter.

Main Steps of the Follicular Phase

The initial step in the follicular phase is the release of follicle-stimulating hormone (FSH) from the pituitary gland.[1,4] The FSH stimulates the ovaries to produce follicles, which are fluid-filled sacs with eggs inside. The follicles begin to develop, and the eggs start to mature.

One follicle develops faster than the other follicles in the ovaries. The follicle that grows more quickly is called the dominant follicle. The dominant follicle then releases additional estrogen into the body. The increased estrogen levels thicken the uterus lining for possible implantation of a fertilized egg. Raised estrogen levels trigger a decrease in FSH, causing the less developed follicles to be reabsorbed back into the body and allowing the dominant follicle to mature fully. The increasing luteinizing hormone leads to the subsequent phases of the menstrual cycle.

At-Home Hormone Testing With Everlywell

With Everlywell, you can access an at-home Women’s Fertility Test to check on five key hormones that can affect your menstrual cycle, ovulation, and ability to become pregnant (sample collection is done at home, and you then mail the sample to a laboratory for testing). The test results will provide detailed information on the five hormones and whether your measurements are within the established normal ranges.

The lab test only requires a simple finger prick to collect a small blood sample, which is then mailed to a certified lab. An independent, board-certified healthcare provider reviews the results. The results are shared with you through a secure, HIPAA-compliant platform.

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  1. Follicular phase of menstrual cycle: Hormone levels & length. Cleveland Clinic. Accessed November 19, 2023.
  2. McLaughlin JE. Menstrual cycle - women’s health issues. Merck & Co, Inc. November 12, 2023. Accessed November 19, 2023.
  3. Menstrual cycle. Office on Women’s Health. Accessed November 19, 2023.
  4. Monis CN, Tetrokalashvili M. Menstrual cycle proliferative and follicular phase.[Updated 2022 Sep 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from:
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