What Your GP Might Not Test For (And Why It Matters for Fertility)
When you visit your GP about fertility concerns, you'll typically get some basic testing after you have been trying to conceive for 6-12 months without success: day 3 hormone levels, maybe a progesterone test, possibly basic thyroid function. These tests are useful, but they often miss crucial pieces of the puzzle, especially if you have underlying health conditions.
Here's what standard NHS fertility testing typically includes, what it might be missing, and why more comprehensive assessment can make a real difference to understanding your fertility health.
Standard NHS Fertility Testing
What you'll usually get if you have been struggling to conceive:
For women:
Day 2-5 hormone panel (FSH, LH, oestradiol)
Basic thyroid function (TSH only)
Sometimes: prolactin, testosterone
What this tells you:
If there are obvious hormonal imbalances
Basic thyroid function
For many women (arguably all women)—especially those with PCOS, endometriosis, thyroid issues, or unexplained fertility challenges—this is far from the complete picture.
What Often Gets Missed
1. Comprehensive Thyroid Testing
Standard test: TSH (Thyroid Stimulating Hormone) only
Why this isn't enough:
Your GP will typically only test TSH and consider your thyroid "fine" if it's within the broad NHS reference range (usually 0.5-4.0 mIU/L). But:
TSH alone doesn't show the full picture. You can have "normal" TSH but low free T4 or T3 (the active thyroid hormones your body actually uses)
The reference range is too broad for optimal fertility. For conception, TSH ideally should be under 2.5 mIU/L
Thyroid antibodies aren't routinely checked. You could have Hashimoto's (autoimmune hypothyroidism) with "normal" TSH
Full thyroid panel includes:
TSH
Free T4
Free T3
Thyroid antibodies (TPO and TG)
Reverse T3 (if conversion is suspected to be an issue)
Why it matters: Thyroid dysfunction—even subclinical—significantly affects fertility, increases miscarriage risk, and impacts pregnancy outcomes. Many women only discover thyroid issues when they struggle to conceive.
2. Progesterone Throughout the Luteal Phase
Standard test: Sometimes single progesterone test on day 21 (or 7 days after assumed ovulation)
What's missing:
A single progesterone measurement tells you if ovulation likely occurred, but doesn't show:
Whether progesterone stays elevated throughout the luteal phase
If you have a luteal phase defect (short luteal phase, inadequate progesterone)
How progesterone changes across your cycle
Why it matters: Adequate progesterone throughout the luteal phase is essential for preparing the uterine lining for implantation. Low or declining progesterone can cause early pregnancy loss or prevent implantation entirely.
Some women ovulate but have inadequate progesterone support afterwards—this won't show up on a single day 21 test if that happened to catch the peak.
3. PCOS Diagnosis Criteria
Standard approach: If cycles are irregular and you have some signs, PCOS might be diagnosed. Or it might be missed entirely.
What's often incomplete:
PCOS diagnosis requires 2 out of 3 criteria (Rotterdam criteria):
Irregular or absent ovulation
Clinical or biochemical signs of hyperandrogenism (excess androgens)
Polycystic ovaries on ultrasound
What gets missed:
Lean PCOS – women who aren't overweight often don't get properly assessed
Comprehensive androgen testing – total testosterone is checked, but free testosterone, DHEA-S, and androstenedione are often not
Insulin resistance testing – fasting glucose and insulin, or glucose tolerance testing, can reveal insulin resistance even when weight is normal
Inflammation markers – useful for understanding overall metabolic health
Why it matters: PCOS is one of the most common causes of fertility issues, but it's frequently under-diagnosed, especially in women who don't fit the "typical" presentation.
Functional Testing
When standard testing doesn't reveal clear answers—or when you want a more comprehensive picture—functional testing can provide valuable insights. Examples include:
DUTCH Test (Dried Urine Test for Comprehensive Hormones)
What it measures:
Sex hormones (estrogen, progesterone, testosterone) and their metabolites throughout your cycle
How your body metabolises and clears hormones
Cortisol patterns (stress hormone)
Melatonin (sleep)
Organic acids that indicate nutritional deficiencies
Why it's useful:
Shows not just hormone levels but how you metabolise them
Can identify estrogen dominance patterns
Reveals cortisol dysregulation that can impact fertility and your HPA axis function
Identifies specific metabolic pathways that may need support
Best for: Women with hormone-related symptoms, stress-related fertility issues, burnout, or when standard testing is "normal" but symptoms persist.
Full Thyroid Panel (Private Testing)
As mentioned above, this goes beyond TSH to include free T4, free T3, and antibodies.
Why it's useful:
Catches subclinical hypothyroidism or Hashimoto's
Identifies poor T4 to T3 conversion
Reveals autoimmune thyroid issues before they're severe enough for NHS diagnosis
Best for: Anyone with fertility concerns, but especially if you have fatigue, weight issues, hair loss, cold intolerance, or family history of thyroid disease.
Gut Health Testing (Comprehensive Stool Analysis)
What it measures:
Gut microbiome diversity and balance
Presence of pathogenic bacteria, parasites, or yeast overgrowth
Digestive function (enzyme production, fat absorption)
Inflammation markers in the gut
Short-chain fatty acid production
Why it's useful for fertility:
Gut health directly impacts hormone metabolism and immune function
Gut dysbiosis (imbalance) is linked to inflammation, which can affect fertility
Your gut microbiome influences oestrogen metabolism
Chronic gut issues can impair nutrient absorption critical for fertility
Best for: Women with digestive issues (IBS, bloating, irregular bowel movements), endometriosis (gut-endo connection), or immune-related fertility issues.
Vaginal Microbiome Testing
What it measures:
Bacterial balance in the vaginal microbiome
Presence of beneficial lactobacilli species
Pathogenic bacteria or yeast overgrowth
pH levels
Why it's useful for fertility:
Vaginal microbiome health affects conception and pregnancy outcomes
Bacterial vaginosis and dysbiosis increase miscarriage risk
An optimal vaginal environment supports sperm survival and implantation
Certain infections can impact fertility without obvious symptoms
Best for: Women with recurrent vaginal infections, unexplained fertility issues, or history of miscarriage.
Nutrient Testing
What can be tested:
Vitamin D
Iron and ferritin
B12 and folate
Zinc
Magnesium
Omega-3 levels
Why it's useful:
Nutrient deficiencies directly impact egg quality, hormone production, and fertility
Iron deficiency is extremely common in women of reproductive age
Low vitamin D is linked to PCOS, endometriosis, and poor fertility outcomes
Testing reveals what you actually need rather than guessing with supplements
Best for: Anyone wanting to optimise fertility and hormone health, especially if dietary intake is limited or you have absorption issues.
When Is Functional Testing Worth It?
Consider functional testing if:
Standard testing is "normal" but you have symptoms or aren't conceiving
You have diagnosed or suspect PCOS, endometriosis, or thyroid issues and want deeper insight
You've had recurrent miscarriages
You have digestive or immune issues
You want to optimise before starting fertility treatment
Your cycles are irregular despite "normal" hormone levels
Functional testing isn't always necessary for everyone, but it can provide answers when standard testing leaves gaps—especially for women with complex hormone or health challenges.
How to Advocate for More Comprehensive Testing
If you feel standard testing isn't giving you the full picture, you can advocate for yourself with the GP.
1. Ask specific questions:
"Can we test free T3 and T4, not just TSH?"
"Could we check thyroid antibodies?"
"I'd like to test insulin and fasting glucose to rule out insulin resistance"
"Can we do progesterone testing at multiple points in my luteal phase?"
2. Be specific about symptoms: Don't just say "I'm tired" or "my cycles are irregular." Document specific symptoms, how often they occur, and how they impact your life.
3. Request referrals: If your GP isn't willing to do more comprehensive testing, ask for a referral to a gynaecologist or endocrinologist who specialises in fertility or women’s health.
4. Consider private testing: If NHS testing is limited and you can afford it, private testing (either through private clinics or functional testing companies) can give you answers more quickly.
5. Work with a nutritional therapist or functional medicine practitioner: We can order and interpret functional testing, then create targeted nutrition and supplement protocols based on your results—working alongside your medical care.
The Bottom Line
Standard fertility testing gives you important baseline information, but it's not designed to catch everything—especially subtle hormone imbalances, nutrient deficiencies, or metabolic issues that significantly impact fertility.
If you've been told "everything is normal" but you know something isn't right, trust yourself to investigate further. More comprehensive testing can reveal what's been missed and give you a clear path forward.
If you're navigating fertility challenges and want support understanding your test results or pursuing more comprehensive assessment, book a free discovery call to discuss whether working together makes sense for you.
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