How do Free Androgen Levels Affect Fertility and Egg Freezing?

Now this one’s quite unique, we know.

While not as common as other hormones on our menstrual board, like oestrogen and progesterone, Free androgen Index still plays a role in helping us understand our fertility.

It’s a marker that helps us understand how much active testosterone is circulating in your body - and that can make all the difference when it comes to ovulation and fertility treatments.

But how exactly does FAI play a role in your fertility journey, and when should you be getting tested for it?

We’re discussing exactly that in this article.

What is Free Androgen Index (FAI)?

The Free Androgen Index isn't actually a hormone itself - it's a calculated ratio or marker that helps us understand how much "active" testosterone is available in your body.

In fact, here’s how to calculate it:

FAI = [Total Testosterone (nmol/L)  ÷ SHBG (nmol/L)] × 100

Now, before it starts feeling like a math class, let’s get back to understanding what this means and why FAI is calculated this way.

Free Androgen Index Normal Range in Females 

Normal FAI values can vary between laboratories, because of different assay techniques. But when your albumin and SHBG levels are normal, here’s the FAI range to look out for:

Source

Here’s also what to remember. In case your albumin or SHBG levels are abnormal, then these results should be interpreted with caution, as it can affect the accuracy of the calculation.

How does FAI affect Fertility?

Typically, only about 1-3% of testosterone in our body is “active” or “available to the cells”. Rest are either attached to SHBG or albumin.

But this active testosterone directly translates to active androgens, affecting our hormones, menstrual cycles and much more.

For instance, elevated levels of FAI could mean more active androgens, affecting ovulation and disrupting hormonal feedback systems and cycles. On the other hand, lower FAI levels could mean androgen deficiency, leading to irregular menstrual cycles, disrupted follicular growth, and so on.

Here’s a glimpse into how FAI can affect fertility:

FAI can disrupt ovulation:

Elevated androgens, indicated by a high FAI, can disturb the hormonal feedback systems (FSH and LH cycles) that regulate normal ovulation.

FAI is a diagnostic marker of PCOS:

Studies confirm that FAI and free testosterone can predict fertility outcomes in infertile PCOS patients. 

FAI levels can dictate treatment response:

Insufficient or high androgen levels can affect the response to treatment during ovarian stimulation as well.

When should I test my FAI levels?

FAI testing is typically recommended when you show signs of elevated androgen levels or as a part of a full hormone test. Here are some reasons why a doctor might consider an FAI test:

• Irregular or missing periods: If your cycles are very unpredictable or stop altogether, it could be a sign of problems with ovulation. This is common in PCOS. The FAI test can show if higher male hormones (androgens) are playing a role.
• Excess hair growth (hirsutism): Extra hair on the face, chest, or body is one of the most visible signs of higher androgens. Checking FAI can help confirm if hormones are driving this.
• Hair thinning or hair loss: Losing hair at the temples or crown of the head in a “male-pattern” style may point toward high androgen levels.
• Persistent acne in adulthood: Breakouts that are severe, hard to treat, or show up later in life can sometimes be linked to higher androgens. FAI testing can help clarify this.
• Trouble conceiving: Since androgens can interfere with ovulation and endometrial receptivity, FAI is often checked as part of fertility testing.
• Suspected or known PCOS: Because PCOS is often linked with elevated FAI, the test is commonly used when PCOS is suspected.‍
• Unexplained weight gain, especially around the belly: Weight changes, particularly when combined with other symptoms like irregular cycles or excess hair, may point to PCOS or other hormone-related causes.

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How is Free Androgen Index Tested?

The Free Androgen Index (FAI) isn’t a direct test on its own. Instead, it’s calculated from two blood tests taken at the same time:

• Total testosterone
• Sex Hormone Binding Globulin (SHBG)

Your doctor uses these results to calculate the index, which helps assess if high male hormone (androgen) levels are affecting your health.

How do I Prepare for my FAI Test?

The FAI test is a simple blood test usually done in the morning (between 7 and 11 am) for accuracy. Once you visit the clinic and settle in, blood is drawn from a vein in your arm. The sample is processed the same day, but results may take a few days.

Now, if you have regular periods, your doctor may recommend testing during the first few days of your cycle (day 2 to 5). If your cycles are irregular or absent, the test can be done anytime, with the timing noted for accuracy.

Here’s what else to keep in mind before taking the FAI test:

• Hormonal birth control or hormone therapy: If you’re on the pill, using a hormonal IUD, or taking hormone replacement therapy (HRT), it’s best to avoid testing or consult a doctor on when to get tested, since these treatments can make results unreliable.
• Medications and supplements: Always let your doctor know about any medicines or supplements you take, especially steroids, anti-seizure medications, or HIV treatments, as these may affect results.
• Biotin (vitamin B7): If you take high-dose biotin (>5mg/day), skip it for at least 8 hours before your test, as it can interfere with results.
• Fasting: While it’s not strictly required for FAI or a female hormone panel, if your doctor is also checking cholesterol, sugar, or insulin, they may ask you to fast overnight.
• Other health factors: Severe illness, major recent weight changes, or testing too soon after pregnancy may temporarily affect results, so your doctor may recommend waiting.

What causes high FAI levels?

If your reports show FAI levels on the higher end, know that this doesn’t have a single cause, but rather could be due to these factors: 

Polycystic Ovary Syndrome (PCOS)

PCOS is the most common reason for a high FAI in women of reproductive age. In PCOS, the ovaries make too many male hormones (androgens), which can cause symptoms like irregular periods, weight gain, acne, and difficulty with insulin regulation.

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Insulin resistance

When your body struggles to respond to insulin, it triggers a chain reaction. Your ovaries start producing more androgens, while at the same time, your SHBG levels drop. 

Remember, SHBG is the protein that binds to these hormones—so when there's less of it, more androgens become "free" and active. This is why FAI goes up. Insulin resistance is common in PCOS, but you can also develop it independently, particularly if you're carrying extra weight.

Thyroid problems

Both an overactive thyroid (hyperthyroidism) and an underactive thyroid (hypothyroidism) can affect SHBG levels, which in turn changes FAI. Hyperthyroidism may lower FAI, while hypothyroidism may raise it.

Ovarian or adrenal tumours (rare)

In rare cases, a sudden rise in androgens — with symptoms like very rapid hair growth, deepening of the voice, or severe acne — could point to a tumour in the ovaries or adrenal glands.

Congenital Adrenal Hyperplasia (CAH)

This is a genetic condition where the adrenal glands don’t make hormones properly, leading to higher androgen levels and a raised FAI.

Obesity

Carrying extra weight can lower SHBG and increase androgen levels, making FAI higher. This effect is even stronger if PCOS and insulin resistance are also present.

Medications

Certain medications — such as anabolic steroids, some antidepressants, or hormonal treatments — may also raise androgen levels and affect your FAI.

What causes Low FAI levels?

Low FAI isn’t as common as high FAI, but it can happen when your body either makes less testosterone or binds up too much of it. Here are some common reasons why it might happen:

High SHBG levels

SHBG is a protein that binds to testosterone in the blood. If there’s too much SHBG, it “locks away” more testosterone, leaving less available for your body to use. This can happen with liver problems, an overactive thyroid, certain hormone therapies (like oestrogen), or sometimes just due to genetic factors.

Low testosterone production

Sometimes the ovaries (or the brain signals that control them) don’t make enough testosterone. This can happen with conditions like premature menopause, pituitary problems, or ovarian dysfunction. When testosterone levels are too low, FAI naturally drops.

Liver disease

Since the liver helps make SHBG, liver problems can upset the balance — often raising SHBG levels and lowering free androgens in the process.

Medications

Certain medicines can affect your hormone balance. For example, oral contraceptives and estrogen therapies tend to raise SHBG, while steroids or anti-androgen drugs can lower testosterone production. Both can lead to lower FAI.

Extreme weight loss or eating disorders

Significant weight loss, restrictive eating, or conditions like anorexia nervosa can disrupt the signals from the brain that regulate the ovaries. This reduces hormone production, including testosterone, and lowers FAI. 

Free Androgen Index and Egg Freezing: What's the Connection?

Before starting an egg freezing cycle, your doctor may check your Free Androgen Index (FAI). This helps doctors assess your hormone balance and can help them predict how your ovaries might respond to the stimulation medicines used in the process.

If your FAI is higher than normal, it may suggest that your body produces more male hormones (androgens). In that case, your doctor might adjust your stimulation plan or even start you on medications such as metformin or inositols, alongside lifestyle changes like healthy weight management and regular exercise, to improve your response.

If your FAI is in the normal range, most women respond well to standard stimulation protocols. And if your FAI is on the lower side, your doctor may take a different approach to encourage better egg development.

Get an Affordable FAI Blood test in the UK, via Amilis

About 751,000 women are waiting for gynaecological care in the UK, of which 30,000 women have been waiting more than a year for an appointment.

Be it egg freezing, getting a comprehensive hormone panel done, or even basic fertility assessments.

So at Amilis, we decided: This narrative, no more.

That's why we are working to make reproductive care accessible and affordable in the UK.

Here's how:

• Get your FAI tested as part of a comprehensive female hormone panel for just 130 (50% less than fertility clinics) with minimal to no wait times.
• Get a free, personalised report on what FAI levels mean for your age, along with other hormones.
• Get free doctor consultations with top fertility experts in the UK, to interpret your results and next steps
• Get free consultations with top fertility clinics in the UK

And throughout, you'll have Amilis experts supporting you on your journey, with 1-1 free calls and guidance.

Figuring out where to get started? Book a free call, or take our personalised fertility quiz to know more!

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Frequently asked questions

Does high FAI affect egg retrieval?

A higher FAI usually means higher levels of male hormones (androgens). This can sometimes affect how your ovaries respond to stimulation and may influence egg quality (as it influences follicular growth). However, patients are usually tested for FAI prior to the procedure, and if the levels are abnormal, the stimulation doses are adjusted accordingly, thus reducing its effect on egg retrieval. 

Can high FAI cause infertility?

Yes, it can. High FAI means there is more active testosterone in the body, which can interfere with the normal signals needed for ovulation. That is why women with PCOS and elevated FAI may have irregular or missing periods, making it harder to conceive naturally. 

How to calculate free androgen index?

FAI is not measured directly. It is worked out from two simple blood tests: total testosterone and sex hormone-binding globulin (SHBG). The lab uses these numbers in this formula:

FAI = [Total Testosterone (nmol/L)  ÷ SHBG (nmol/L)] × 100

Which gives your doctor the index.

What does the free androgen index indicate?

FAI gives an estimate of how much “free” or active testosterone is in your blood. It is a useful way to check for androgen excess, especially in conditions like PCOS where too much testosterone is often part of the picture.

Can FAI help diagnose PCOS?

Along with symptoms and ultrasound findings, a raised FAI is one of the key markers doctors look at when diagnosing PCOS. It helps confirm the presence of androgen excess, which is central to the condition.

What is the normal range of free androgen index?

It can vary depending on the lab, but for women of reproductive age, it is usually between 0.7 and 6.4 per cent. A higher result may suggest androgen excess, as seen in PCOS, while a lower one may mean your body is not making enough testosterone.