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Birla Fertility & IVF
Birla Fertility & IVF

Ovarian Follicle Size for Conceiving

  • Published on April 16, 2022
Ovarian Follicle Size for Conceiving

Becoming parents is a dream for many, yet only some have an easy path to conception. Questions like ‘Why can’t I conceive?’ are too common among hopeful parents. Therefore, understanding your body is the first step, particularly the importance of egg and ovarian follicle size for pregnancy. The normal ovarian follicle size for conceiving is between 18-22 mm in diameter.

To find out why ovarian follicle size is relevant for pregnancy, let’s begin by exploring what an ovarian follicle is.

What is an Ovarian Follicle?

An ovarian follicle is a fluid-filled sac containing multiple immature eggs. Typically, a female is born with nearly 1 to 2 million follicles that start to decline as they grow old. By the time they reach puberty, they have a total of 300,000 to 400,000 follicles.

After puberty, each month during your menstrual cycle, a select group of follicles begin to grow and mature. In the ovulation phase, the follicle size increases as it matures and prepares to release the egg for fertilization.

What role does the Follicle size play in fertility treatment?

A wide range of fertility treatments for women includes ovarian stimulation. Your fertility doctor provides certain hormones and drugs to induce the development of follicle size and quality in your ovaries. These hormones stimulate the production of healthy and mature eggs. Common hormone injections include follicle-stimulating hormone (FSH), luteinizing hormone (LH) or both.

During fertility treatment like In Vitro Fertisation IVF, fertility specialists consider an ovarian follicle size of 18–20 mm (1.8–2 cm) in diameter which is optimal for fertilization and to achieve successful pregnancy.

Therefore, ovarian stimulation is an important step to achieving the optimal ovarian follicle size for conceiving during fertility treatments such as IVF and IUI. While it is possible to achieve conception even with one mature follicle, it is preferable to have more follicles while undergoing fertility treatments. The doctor suggests a routine pelvic ultrasound to regularly monitor the follicle’s number and size

What are the Development Stages of Ovarian Follicles?

The process of development and maturing of ovarian follicles is called folliculogenesis. Let’s discuss the different stages of ovarian follicles:

  • Primordial Follicles: Follicular development starts in the fetus. By five months in, a baby girl has 1-2 million follicles and stays until puberty.
  • Primary Follicle: Primordial follicles begin to develop and mature further when a woman reaches puberty. It is further divided into early and late bloomers.
  • Secondary Follicle: These upgraded follicles start assembling a team of cells that contribute to estrogen production.
  • Antral Follicle (Graafian Follicle): ast stage, is when the follicle is fully mature and ready to release during ovulation, with one follicle taking the lead while the rest keeps on growing.

What is the Dominant Ovarian Follicle?

The “leading follicle,” or dominant ovarian follicle, is an essential component of the female reproductive system. It grows larger and more quickly than the other follicles. This also predicts when ovulation will occur and increases the likelihood of successful conception. In addition, it helps in monitoring the chances of assisted reproduction techniques (ART) such as IUI and IVF.

How does Ovarian Follicle Size Affect Pregnancy?

Ovarian Follicle size plays a key role in determining your chances of getting pregnant as it ensures the ovulation process.

Nearly on the 14th day of your cycle, your follicles complete their development and begin to rupture. This process supports the release of a healthy, mature egg. The egg released from the follicle sac travels down the fallopian tube to be fertilised with sperm.

The chances for a healthy pregnancy depend on the proper growth of follicle size. Ovarian follicles are also responsible for the secretion of the estrogen hormone – which thickens the uterus wall and prepares it for pregnancy.

What Factors Affect the Changes in Ovarian Follicle Size?

Several variables can affect a woman’s ovarian follicle size, such as:

  • Menstrual Cycle: During the first half of the cycle, the ovaries prepare and grow follicles, which then decrease in size after ovulation.
  • PCOS: With PCOS, your ovaries are filled with tiny cysts (undeveloped follicles), leading to a noticeable size increase.
  • Ovarian Cysts: Any cyst, whether just passing through or sticking around, can bulk up your ovaries affecting the size of follicles.
  • Hormonal Imbalances: If your hormones are unbalanced, like in hyperstimulation syndrome, your ovaries might get swollen impacting the follicle size.
  • Age: Heading towards menopause means your ovaries and follicles size are gradually downsizing in both size and activity and so are follicles.
  • Medication: Certain medicines, especially those for IVF, can affect your ovarian follicle size

Can Ovarian Follicle Size Impact Fertility?

Your reproductive health is majorly dependent on your follicles’ size and the quality of the eggs.

If you have a good size and number of follicles, your potential of getting pregnant is higher as you have an abundance of immature eggs that can develop and burst leading to ovulation.

Furthermore, your follicle size and number begin to decline as you age. Therefore, it is recommended that women should try to conceive at an early age because the follicles’ size, number and quality are at their peak.

How is ovarian follicle size measured?

Ovarian follicle size can be measured with AFC. The antral follicle count (AFC) test is a transvaginal ultrasound that helps evaluate a woman’s ovarian follicle size and count. Follicles are visible and can be counted at the antral stage through the AFC test.

Besides evaluating the ovarian reserve, the antral follicle count test can help discover the following:

  • Provides an idea of how your age is affecting your fertility
  • Identifies premature ovarian failure
  • Helps diagnose polycystic ovarian syndrome (PCOS)
  • The size of follicles

If you are aged between 25 and 34 years, your antral follicle count should be nearly 15. And, if you are above the age of 35, your antral follicle count may drop to 9 or lower. The normal size of follicles for pregnancy is determined by an average diameter of 18-25 mm.


Understanding the right ovarian follicle size for conceiving is important for couples as it helps to enhance their chances of successful pregnancy. This article provides detailed information on ovarian follicle and their size for pregnancy. If you are trying to conceive and facing issues regarding follicle or egg quality & quantity, consult our fertility specialist by calling the given number or filling out an appointment form with the required details or you can visit our Fertility Centers.

Written by:
Dr. Meenu Vashisht Ahuja

Dr. Meenu Vashisht Ahuja

Dr. Meenu Vashisht Ahuja is a highly experienced IVF specialist with more than 17 years of experience. She has worked with renowned IVF centers in Delhi and is a member of esteemed healthcare societies. With her expertise in high risk cases and recurrent failures, she provides comprehensive care in the field of infertility and reproductive medicine.
Rohini, New Delhi

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