Follicular Phase

What is the follicular phase of the menstrual cycle?

The follicular phase refers to that part of your menstrual cycle when an egg matures in your ovaries. It’s part of an ongoing process in your body during your reproductive years when hormones activate changes in your body that make it possible for you to become pregnant.

Your menstrual cycle consists of two phases: the follicular phase and the luteal phase. Menstruation (your period) and ovulation are important events during your cycle that correspond with each phase.

• During menstruation, or your period, you shed your uterus lining (endometrium) through your vagina. The follicular phase begins on the first day you menstruate. It lasts until ovulation, when one of your ovaries releases a mature egg.
• During the follicular phase, fluid-filled sacs in your ovaries called follicles house immature eggs. One of these follicles, the dominant follicle, houses an egg that’s bigger and healthier than the rest. The follicular phase is the longest phase of your menstrual cycle.
• During ovulation, your ovary releases the egg that matured during the follicular phase. It begins its journey to your fallopian tubes. Ovulation marks the end of the follicular phase and the beginning of the luteal phase.
• During the luteal phase, the dominant follicle that released the mature egg changes into a structure called the corpus luteum. The corpus luteum produces important pregnancy hormones. If you don’t get pregnant, the corpus luteum will disappear, and you’ll shed your uterus lining (menstruation).

With menstruation, the cycle repeats.

What happens during the follicular phase of the menstrual cycle?

You’re born with about a million eggs. This reserve declines as you grow older. Once you start menstruating, your body begins a process of maturing these eggs. Only a select few fully mature over your lifetime. During the follicular phase of your menstrual cycle, around 11 to 20 eggs begin developing, but only one matures completely.

Hormones in your brain and your ovaries regulate the changes in your body that make this process possible.

1. Your pituitary gland releases follicle-stimulating hormone (FSH). A part of your brain called your hypothalamus controls your pituitary gland. Your pituitary gland helps your body make the hormones it needs to regulate important processes. The FSH from your pituitary gland activates your ovaries to start producing follicles, the fluid-filled sacs where your eggs can mature.
2. A dominant follicle forms. A single follicle, called the dominant follicle, starts to develop more quickly than the other follicles in your ovaries. As the dominant follicle matures, so does the egg inside that will eventually be released when you ovulate.
3. The dominant follicle releases more estrogen into your body. The increased estrogen thickens your uterus lining so that a fertilized egg (embryo) can implant there. This stage is sometimes called the proliferative phase.
4. The increased estrogen triggers a decrease in FSH. Your pituitary gland responds to the increase in estrogen by decreasing the amount of FSH it produces. This decrease causes the other follicles to begin to wither away and reabsorb into your body. Meanwhile, the egg inside the dominant follicle reaches full maturity.

Toward the end of the follicular phase, high estrogen levels trigger your pituitary gland to release a surge of luteinizing hormone (LH), the hormone associated with the luteal phase. LH activates the mature egg to escape the follicle and the ovary (ovulation).

What is the normal time range for the follicular phase?

The average menstrual cycle lasts from 28 to 35 days. The follicular phase ranges from 14 to 21 days. The luteal phase lasts about 14 days. Unlike the luteal phase, which stays fairly consistent, the length of your follicular phase may vary at different stages of your life.

The length of your follicular phase depends on how long it takes the dominant follicle to form a fully matured egg.

Long follicular phase

Having a long follicular phase doesn’t mean you’re less likely to become pregnant. A long follicular phase most likely means that your menstrual cycle is longer, too. You can have a long follicular phase for a variety of reasons:

• It’s just your body’s normal timetable.
• You’re taking birth control that’s lengthening your follicular phase.
• You have a vitamin D deficiency.

Short follicular phase

A short follicular phase could indicate that you may have trouble becoming pregnant. It’s common for your follicular phase to shorten (for example, from 14 days on average to 10 days) as you approach menopause. Menopause signals a shift in your life when you no longer get your period.

Starting in your late 30s, your FSH levels may still increase during your follicular phase, but your LH levels may not spike as they did previously. As a result, the follicle may mature faster than the egg inside and release it too soon. These eggs may not be viable for pregnancy.

Can you get pregnant during the follicular phase?

Yes. You have the greatest chance of becoming pregnant if you have intercourse during the five days leading up to ovulation and on the day you ovulate. This timetable provides an ideal window for an egg and sperm to meet. Ovulation calendars can help you keep track of your cycle.

What are the symptoms of the follicular phase?

Your body temperature at rest provides clues about the various phases of your menstrual cycle. Knowing when you’re in the follicular phase can be useful if you’re trying to become pregnant.

Take your temperature each morning at the same time, right after you wake. During the follicular phase, your temperature should range between 97 and 97.6 degrees Fahrenheit. It should increase during ovulation and remain elevated when you’re in the luteal phase.

A note from Cleveland Clinic

Knowing when the various phases of your menstrual cycle are occurring can help you plan the best time to try for a baby. You have the best chance of becoming pregnant in the days surrounding ovulation, including the end of the follicular phase. Speak to a healthcare provider or a fertility specialist about the best strategies for tracking your cycle and symptoms to increase your likelihood of becoming pregnant.