What is the follicular phase of the menstrual cycle?

What is the follicular phase and when does it start?

The follicular phase is the first phase of the menstrual cycle. It starts on the first day of your period and lasts until ovulation. This phase usually lasts about 14 days for women who have a 28-day cycle. However, some women have shorter and longer cycles, so the length of the follicular phase may vary from woman to woman.

What happens during the follicular phase of a period cycle?

You are born with all the eggs you’ll ever have. This is called your ovarian reserve. Over the course of your lifetime, this gradually declines. For example, at birth you’ll have anywhere between 1-2 million eggs. By the time you reach puberty, you’ll have 300,000 to 500,000. These immature eggs (called oocytes) are found in the primordial follicles, which are located inside the ovaries.

Most of the primordial follicles remain in a dormant state known as the primordial follicle stage. However, during the lead up to the follicular phase, lots of changes occur to these follicles.

After menstruation, a small number of primordial follicles are ‘recruited’ to start growing. When this happens, they enter the what’s called the primary follicle stage. The majority of these follicles will eventually shrink and die off. Usually in a natural cycle, only one follicle will continue to develop, until one egg is ovulated.

Follicles and eggs within them start developing three months prior to the menstrual cycle in which a dominant egg is selected and released. This highlights the importance of looking after your health and wellbeing for several months prior to trying to fall pregnant.

Hormonal changes during the follicular phase

This process of follicle selection is essential for natural fertility. While multiple follicles begin to mature early in the follicular stage, only one will become the dominant follicle and release an egg during ovulation. This ensures that only one mature egg is produced during ovulation, giving it a chance to be fertilised.

Several hormones are involved in regulating the follicular phase.

Follicle stimulating hormone (FSH) stimulates several follicles to grow.

As follicles grow, they produce the hormone oestrogen. The dominant follicle becomes the largest and produces the most oestrogen. This inhibits the growth of other follicles.

When the dominant follicle reaches its peak size, levels of luteinising hormone (LH) and follicle stimulating hormone (FSH) surge, which triggers the final maturation of the egg and ovulation.

As the dominant follicle matures it secretes inhibin. This, along with the rise in oestrogen, suppresses FSH production which prevents more follicles from developing and ensures that only one follicle becomes the dominant one.

Symptoms of the follicular phase

The follicular phase begins when you get your period. Other signs you’re in the follicular phase include:

• Cervical mucus changes: After your period, cervical mucus tends to be dry or minimal. However, as oestrogen rises, it becomes more abundant, thin, and slippery – a sign your body is gearing up for ovulation.
• Increased energy: Increased oestrogen levels may make you feel more energetic or motivated.
• Cravings and mood shifts: Fluctuating hormones can lead to changes in mood, cravings, or even some mild bloating.

Tracking your menstrual cycle, ovulation, and the symptoms you experience can help you identify when you're in the follicular phase.

Why the follicular phase matters for conception

The follicular phase matters for conception for several reasons.

Follicle development: The primary function of the follicular phase is to prepare the highest quality egg available for ovulation.

Egg quality: If follicular development is impaired it may reduce the quality of the egg released during ovulation.

Endometrium development: Hormonal changes that occur in the follicular phase cause the uterine lining (endometrium) to thicken, which is crucial for successful implantation and early pregnancy.

Sperm survival: The cervical mucus produced in the follicular phase helps protect sperm, allowing them to survive for several days while waiting for ovulation.

When to seek help

Fertility can vary greatly from person to person so it can be hard to know when to seek help. However, there are key situations where you should consult with a fertility specialist.

You’ve been trying to conceive for a year without success

If you’re under the age of 35 and have been trying to conceive for 12 months or more, make an appointment to see a fertility specialist.

Women over 35 should seek help after 6 months due to the rapid decline in fertility after this age.

You have irregular or absent periods

If your periods are irregular or you miss periods altogether, it may indicate underlying fertility issues. Consulting with a fertility specialist can help diagnose any potential issues early on.

You have known medical conditions that impact fertility

Certain medical conditions can significantly affect a woman’s ability to conceive, including:

• polycystic ovarian syndrome (PCOS)
• endometriosis
• fibroids
• previous pelvic infections or surgery.

If you have these conditions it’s important to seek fertility advice even if you haven’t been actively trying to conceive yet. These conditions can cause issues with ovulation, egg quality, or the uterine environment, making it harder to fall pregnant when you want to.

You have painful periods or pain during sex

Painful periods or pain during sex can be signs of endometriosis which can affect fertility. If you’re experiencing these symptoms and want to have a baby, we recommend you see a fertility specialist.

Your partner has known fertility issues

Fertility issues can affect both partners. If your male partner has a history of low sperm count, low motility, or any known health conditions affecting his reproductive health, it’s important for both partners to seek evaluation from a fertility specialist.

Male infertility cannot be underestimated. Rates of male infertility are increasing substantially with male factor infertility being a primary or contributing factor in around 50% of couples.[1]

You’re over 35 and trying to conceive

By 35, fertility begins to decrease significantly, which can make conception more challenging. Women who are 35 or older should seek fertility advice if they haven’t fallen pregnant within 6 months of trying. Women over 40 should seek help even earlier, as the chances of conceiving naturally decrease substantially, while the risk of miscarriage and chromosomal abnormalities rises.

You have a family history of infertility

Conditions such as endometriosis or premature menopause can run in families. It’s important to seek advice early if you have a family history of those conditions.

Male infertility can also be inherited through several genetic mutations, so it’s important to ask whether your male partner or any member of his family has any fertility issues.

You or your partner are a known carrier of a genetic condition or have a family history of a genetic disorder

If you or your partner are carriers of a genetic condition you run the risk of having a child with a serious condition. Speaking to a fertility specialist early can help you identify risks and the best options for you.

Regardless of your situation, a fertility specialist can provide personalised guidance and treatment to maximise your chances of having a baby. To book a consultation, contact us below. 

[1] Agarwal A, Baskaran S, Parekh N, et al. Male infertility. Lancet. 2021;397(10271):319-333. doi:10.1016/S0140-6736(20)32667-2