If you've been trying to conceive for a year without success, your fertility doctor may recommend intrauterine insemination (IUI) to give you a better chance of getting pregnant. But did you know that the size of your ovarian follicles can affect the outcome of IUI?
To better understand how follicles affect IUI, let's first learn what they are and what the ideal follicle size is for it.
What is an ovarian follicle?
An ovarian follicle is a fluid-filled sac located in each ovary. Initially, each follicle contains an immature egg, but during the menstrual cycle, several follicles begin to develop. In a typical 28-day cycle, only one follicle usually matures fully, reaching its optimal size and releasing the egg inside it around day 14.
As the egg is only released once the follicle has reached its ideal size, follicle size can affect the timing of ovulation and the quality of the egg. It also helps fertility specialists determine whether an egg is mature and ready for fertilisation.
However, the number of ovarian follicles is limited. At birth, the ovaries contain around 1-2 million follicles, which decreases to around 300,000 by the time puberty begins and to just 1,000 by the time menopause takes place.
What is the ideal follicle size for IUI treatments?
Since an intrauterine insemination is timed to coincide with ovulation, it's important that the follicle be at a certain size before releasing an egg. The ideal follicle size for IUI typically ranges from 18 to 24 millimetres in diameter, with the specific range depending on the fertility medications your specialist recommends:
18-20 mm for IUI cycles using oral medications such as Clomid or Letrozole
18-24 mm for IUI cycles using injectable gonadotropins
To ensure that your follicles reach the ideal size, your doctor will monitor their growth using a transvaginal ultrasound. This imaging technique allows the doctor to check follicle growth before carrying out the insemination procedure, thereby increasing your chances of conceiving.
You will typically have monitoring appointments every 1-2 days until at least one follicle has matured. At this point, your doctor will schedule the IUI procedure. In some cases, you may be given some medication to stimulate several follicles to mature.
To find out about your follicle size before undergoing an IUI procedure, schedule an appointment with Thomson Fertility Centre. Our fertility specialist can monitor the growth of your ovarian follicle development and ensure your IUI is timed to give you the best possible chance of success.
What factors affect your follicle development?
As follicle size is important for determining the optimal time for an intrauterine insemination procedure, there are several factors that can affect their development prior to reaching the ideal size. These factors include:
Age:
As you get older, particularly after 35, the maturation of follicles in the ovary (known as the follicular response) may decline. This means that follicles may take longer to reach their ideal size.
Ovarian reserve:
The number and quality of the remaining eggs in the ovaries, known as the ovarian reserve, play a crucial role in follicle development. Therefore, if ovarian reserve is low, fewer follicles may develop in each cycle.
The ovarian reserve is typically assessed through anti-Müllerian hormone tests or ultrasound scans that evaluate the number of antral follicles.
Fertility medication:
Some fertility medications can affect follicle development. For instance, oral medications such as Clomid encourage the maturation of one or two follicles, while injectable gonadotropins stimulate multiple follicles simultaneously.
Polycystic Ovary Syndrome (PCOS):
PCOS is a long-term health condition characterised by hormonal imbalances and metabolic issues, resulting in an abundance of immature ovarian follicles that are unable to mature.
Response to treatment:
The way each person responds to fertility treatments can sometimes affect follicle development. Some women's follicles are slower to grow, or they need higher doses of medication. While others develop many follicles quickly.
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How does the size of my follicle affect the success of my IUI treatment?
Your follicle is like a protective home for your developing egg. When your follicle is too small (under 18 mm), the egg inside is probably not mature enough to be fertilised. Conversely, if the size of your follicle exceeds 24 mm, it may indicate that the egg is no longer suitable for fertilisation.
The ideal size range, typically 18-24 mm, ensures that your egg is released at the optimal moment to ensure successful fertilisation.
What happens if my follicles are not growing?
If your follicles aren't developing as expected during monitoring by your doctor, there is no need to worry. Your doctor can do a few things to help, such as:
Adjust your medication dose to provide more stimulation
Switch medications (e.g. from oral drugs to injectable gonadotropins)
Delay your IUI cycle to give your follicles more time to develop properly
They can also cancel the cycle if the risk of failure or overstimulation is too high
In some cases, your doctor may recommend postponing the IUI cycle if there's concern about poor response or risk of overstimulation
To ensure your safety and a successful conception, your fertility specialist will discuss these options with you. For further information about the optimal follicle size prior to your IUI procedure, schedule an appointment with Thomson Fertility Centre.
Is there any way to increase the follicle size?
While there is no direct way to increase follicle size, certain lifestyle changes can support follicular development and improve egg quality. These include:
Eating a nutritionally balanced diet that is rich in lean protein, antioxidants, omega-3 fatty acids, and vitamins.
Stay well-hydrated by drinking at least 2-3 litres of water throughout the day to support your body's natural functions.
Depending on your individual needs, it may be beneficial to take supplements containing zinc, coenzyme Q10 (CoQ10), iron, vitamins D and B6, selenium, and folic acid.
Maintain an ideal body weight, as being underweight or overweight can affect fertility.
Engage in regular moderate exercise, such as walking, swimming, or yoga, to help reduce stress and support your overall health.
Aim to get 7-9 hours of sleep each night to support hormonal balance and overall well-being.
Manage stress by practicing techniques such as meditation, maintaining a positive attitude, and doing breathing exercises.
Adopting these healthy lifestyle habits helps provide your body with the essential nutrients required for optimal follicle development and increases the chance of conception.
FAQ
What size follicle is required for successful IUI?
The ideal follicle size for triggering ovulation during IUI is usually between 18 and 24 mm in diameter. When your follicle reaches this size, it’s considered mature and is most likely to release a healthy, fertilisable egg in response to medication or a natural hormone surge.
Your doctor will monitor your follicles using ultrasound and typically recommend a trigger shot once at least one has reached 18 mm or more.
What is the normal follicle count for IUI?
The ideal number of mature follicles for IUI depends on factors such as your age, diagnosis, and treatment plan.
- When using oral medications such as Clomid or Letrozole, doctors typically aim for one or two mature follicles, as this increases the likelihood of pregnancy while minimising the risk of multiple pregnancies.
- However, with injectable gonadotropins, it is common to have 2-4 mature follicles, but close monitoring is needed to reduce the risk of overstimulation and multiple pregnancies.
Although having more mature follicles can increase your chance of conceiving, they also raise the likelihood of twins or even a multiple pregnancy. Your fertility specialist will tailor your treatment to balance effectiveness and safety.
Can a 16 mm follicle have a mature egg for IUI?
Yes, a 16 mm follicle can sometimes contain a mature egg, especially in younger women, natural cycles, or when follicles develop quickly. However, it’s a bit less predictable than follicles measuring 18 mm or more, so your doctor will often aim for a slightly larger size before triggering ovulation if possible.
Is a follicle measuring 24 mm too big for IUI?
Not necessarily. A 24 mm follicle is still within the normal range for maturity, and many successful pregnancies result from follicles of this size. However, if a follicle grows much larger (26 mm or more), there is a higher chance that it has already ovulated or that the egg is past its best.
This is why your doctor will typically trigger IUI when the follicle measures around 20-22 mm, to catch the optimal window.
What size follicle is likely to result in twins with IUI?
The presence of two or more mature follicles, typically measuring ≥18 mm, at the time of ovulation increases the likelihood of twins. If you have two or more follicles measuring 18 mm or more, the risk of twins or higher-order multiples increases.
Studies show that the likelihood of having twins is around 5–10% with two mature follicles and up to 20% or more with three to four follicles.
What is the best size egg for IUI?
The mature egg itself can’t be measured on ultrasound but is usually released when the follicle measures around 18-24 mm. Sometimes, particularly in younger patients or fast-growing cycles, a 16 mm follicle may already contain a mature egg.
However, your doctor will usually aim to trigger ovulation when follicles reach 18 mm or more, as this provides the best chance that the egg is fully mature and ready for fertilisation.
The information provided is for general guidance only and should not be considered as medical advice. For a personalised fertility consultation and tailored advice, schedule an appointment with Thomson Fertility Centre today.
For more information, contact us:
Thomson Fertility Centre
- Paragon: 6252 7766
Thomson Specialists (Women's Health)
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