If you've been trying to conceive for a year without success, your fertility specialist may discuss intrauterine insemination (IUI) as one of the treatment options that may be suitable for your individual circumstances. 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.
Follicle size helps your fertility specialist assess follicle development and determine the appropriate timing for treatment. 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 to help determine the appropriate timing for the IUI procedure.
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 follicles and advise on the most appropriate timing for your treatment.
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 before they reach the size your fertility specialist is monitoring. 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 ovarian follicle 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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Why is follicle size monitored during 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 may not yet be fully mature.On the other hand, if a follicle measures more than 24 mm, it may suggest that the egg has become over-mature, which can affect its suitability for fertilisation.
The ideal size range, typically 18-24 mm, helps your fertility specialist determine the appropriate timing for the IUI procedure.
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 depending on your response to treatment
In some cases, your doctor may recommend postponing the IUI cycle if there's concern about poor response or risk of overstimulation
Your fertility specialist will talk you through these options and help you understand what may be most appropriate for your individual circumstances. 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 your overall health during fertility treatment. 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, your doctor may recommend certain supplements, such as zinc, coenzyme Q10 (CoQ10), iron, vitamins D and B6, selenium and folic acid.
Maintain an ideal body weight, as being underweight or overweight may 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 your overall wellbeing.
Manage stress by practicing techniques such as meditation, maintaining a positive attitude, and doing breathing exercises.
Adopting healthy lifestyle habits can help support your overall well-being and provide your body with the nutrients needed for reproductive health, including follicle development.
FAQ
What follicle size is usually monitored before IUI?
In IUI treatment, a follicle measuring around 18 to 24 mm is generally considered mature enough for ovulation to be triggered. At this stage, the egg is usually thought to be ready for release in response to a trigger injection or the body’s natural hormone surge.
Your fertility specialist will monitor your follicles with ultrasound and may recommend a trigger injection once at least one follicle has reached an appropriate size, depending on your individual treatment plan.
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 may be appropriate depending on your treatment plan, while also taking into account the risk of multiple pregnancy.
- 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.
While having more mature follicles may increase the likelihood of pregnancy, it can also raise the chance of twins or multiple pregnancy. Your fertility specialist will guide you on the most appropriate treatment approach based on your individual circumstances and treatment goals.
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?
Follicles measuring around 24 mm may still be considered within the expected range for treatment, depending on your individual circumstances. 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 follicle size may be associated with twins in IUI?
If two or more mature follicles, usually measuring 18 mm or more, are present at the time of ovulation, the chance of twins or multiple pregnancy may be higher during IUI treatment.
Published figures from some studies have reported that:
- Two mature follicles may be associated with a twin pregnancy rate of around 5–10%
- Three to four mature follicles may be associated with a higher chance of twins or higher-order multiple pregnancy, with some reports suggesting 20% or more
Your fertility specialist will take this into account when guiding your treatment plan and discussing the possible risks of multiple pregnancy.
What is the usual follicle size for IUI?
The egg itself cannot be measured on ultrasound, but it is usually released from a follicle once the follicle reaches around 18 to 24 mm. In some cases, particularly in younger women or in faster-growing cycles, a 16 mm follicle may already contain a mature egg.
In most IUI cycles, your fertility specialist will usually consider triggering ovulation once at least one follicle has reached around 18 mm or more, as this is generally considered an appropriate stage of follicle maturity.
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
- Novena: 6399 3758, 8811 0358 (WA)