What is the follicular phase of the menstrual cycle. How long does it last?

By (embryologist) and .
Last Update: 12/23/2022

The follicular phase is the first phase of a woman's menstrual cycle, in which the hormone FSH (follicle stimulating hormone) and estrogens are the main hormones.

The menstrual cycle begins with menstruation, so the first day of menstrual bleeding marks the beginning of the cycle and the start of the follicular phase.

This phase extends over a more or less variable period of time, but covers about 14 days in a typical 28-day menstrual cycle until ovulation occurs, i.e. the expulsion of a mature egg from the ovary.

What is the follicular phase?

The follicular phase is one of the phases into which the female menstrual cycle can be divided. Specifically, the follicular phase is the first phase of the cycle, which begins with the onset of menstruation.

Thus, we can speak of three phases of the menstrual cycle:

Follicular Phase
this phase is characterized by the development of several follicles in the ovary, by the action of the FSH hormone or follicle stimulating hormone. However, only one of them will complete this development, which is why it is called the dominant follicle dominant follicle. This phase spans from menstruation to ovulation.
Ovulation phase
the dominant follicle expels the mature egg it contains in a process known as ovulation.
Luteal phase
the remains of the empty follicle in the ovary will form the corpus luteum, which will be responsible for secreting the progesterone that characterizes this phase of the menstrual cycle. The luteal phase extends from ovulation until the arrival of the next menstrual period (if pregnancy has not occurred).

Therefore, the follicular phase is a pre-ovulatory period in which follicular development takes place, leading to the release of an egg into the fallopian tubes, where it will await the possible arrival of a sperm to be fertilized.

In the following article you can read more detailed information about the menstrual cycle: The menstrual cycle: what happens in each of its phases?

What happens in the follicular phase?

During a woman's menstrual cycle, it is important to be aware of the changes that occur in both the ovaries and the uterus. In this case, the following are the main changes that occur at both levels in the follicular phase of the cycle.

In the ovary

The secretion of FSH hormone by the pituitary gland (in the brain) stimulates the development of several follicles in the ovary. However, one of the follicles will grow over the rest by a process of selection and dominance, the dominant follicle. Instead, the remaining follicles in the cohort will not continue their development and will degenerate in a process known as atresia.

Follicular development will cause the follicular granulosa cells to secrete estrogens. In this way, there will be an increase in estrogen levels as the follicular phase progresses, due to the large production of the dominant follicle, until it reaches such high levels that it will produce (possibly also aided by the hormone progesterone) the discharge of large amounts of LH or luteinizing hormone. This LH peak triggers ovulation and thus the end of the follicular phase.

In the uterus

The follicular phase of the menstrual cycle begins with menstruation, so the uterine endometrium will be shed and expelled through the vagina in menstrual bleeding.

However, increasing estrogen levels as the ovarian follicular phase progresses lead to endometrial proliferation. Thus, the endometrium is said to undergo a proliferative phase in which it will regenerate from its basal layer proliferative phasephase in which it will regenerate, starting from its basal layer.

In addition, the cervical mucus (produced by the cervix) also undergoes changes due to increased estrogen levels during the follicular phase. While cervical mucus is scanty during menstruation, as estrogen increases it will become more abundant, elastic and transparent (like raw egg white). This change will allow sperm to pass through the cervix close to ovulation.

How long does the follicular phase last?

In a typical 28-day menstrual cycle, the follicular phase lasts about 14 days, until the time when ovulation is expected to occur. Of these, the first 3-6 days correspond to menstruation. However, the follicular phase of the menstrual cycle is usually the most variable of all.

Therefore, when the menstrual cycle lasts more or less than 28 days, it usually corresponds to a lengthening or shortening of the follicular phase.

Stress, travel that involves a time change, sudden weight changes and strenuous physical exercise are factors that can affect the entire hormonal control that regulates the menstrual cycle. In case of irregular menstrual cycles, it is best to visit a specialist so that he/she can check that everything is all right.

FAQs from users

Is pregnancy possible in the follicular phase of the menstrual cycle?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Yes, although ovulation must have occurred for fertilization to occur and the egg must be in the fallopian tubes, a woman can become pregnant in the follicular or pre-ovulatory phase.

The reason is that sperm survive for a period of about 3-5 days in the woman's reproductive tract, so pregnancy could occur from sexual intercourse days before ovulation.

However, the egg only survives for about 12-24 hours after ovulation. Therefore, a woman's most fertile days are the 3-5 days before ovulation, the day of ovulation and the day after ovulation.

However, calculating the day when the follicular phase ends and ovulation occurs can be complicated. The day of ovulation can be variable, although the length of cycles is predictable. Therefore, it is best to combine the calendar method of estimating ovulation with other methods such as increased basal body temperature, the appearance of cervical mucus or, more accurately, with ovulation tests that detect the LH hormone in urine.

Are the pre-ovulatory phase and the follicular phase of the menstrual cycle the same thing?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

Sí, la fase folicular del ciclo menstrual es la fase del ciclo que va desde el inicio de la menstruación hasta la ovulación. Therefore, it is the preovulatory period of the menstrual cycle and, for this reason, this phase may also be known as preovulatory phase.

On the other hand, it is also possible to know the follicular phase as the estrogenic phase, due to the increase in this hormone that occurs.

How is the flow in the follicular phase?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

The discharge that a woman may observe will vary throughout the follicular phase. During menstruation, it will be scanty and will go unnoticed with the menstrual bleeding.

Subsequently, in the days following menstruation, a thin, sticky mucus will be observed, which will become more abundant, transparent, elastic and filmy as the follicular phase progresses and ovulation approaches.

This is why periovulatory mucus is said to have an appearance similar to raw egg white.

Suggested for you

If you want to learn more about ovulation, we recommend reading the following article: When does ovulation occur and what are the symptoms?

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FAQs from users: 'Is pregnancy possible in the follicular phase of the menstrual cycle?', 'Are the pre-ovulatory phase and the follicular phase of the menstrual cycle the same thing?' and 'How is the flow in the follicular phase?'.

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 Silvia Azaña Gutiérrez
Silvia Azaña Gutiérrez
B.Sc., M.Sc.
Graduate in Health Biology from the University of Alcalá and specialized in Clinical Genetics from the same university. Master in Assisted Reproduction by the University of Valencia in collaboration with IVI clinics. More information about Silvia Azaña Gutiérrez
License: 3435-CV
Adapted into english by:

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