You got your results back. Everything is normal.
And yet you're exhausted. Your cycles are irregular. You've been trying to conceive for longer than you expected. You don't feel fine but on paper, you are.
This is not in your head. And it is not a mystery.
It comes down to a distinction that conventional medicine rarely explains: the difference between normal and optimal.For women navigating fertility challenges, this gap is not a technicality. It is often the entire story.
Why "Normal" Is Not Enough
Standard lab reference ranges are statistical constructs, not clinical benchmarks.
They are calculated from the central 95% of values in a large reference population a population that includes people who are overweight, sedentary, insulin resistant, and sub-fertile. Falling within this range means you resemble the average. It says nothing about whether your body is functioning well enough to conceive, sustain a pregnancy, or feel genuinely healthy.
Functional medicine uses a different standard: evidence-based optimal ranges derived from research into actual outcomes. The question is not "Is this result abnormal? but "Is this result good enough?"
For fertility specifically, the answer is often no even when your doctor says otherwise.
Four Markers That Illustrate the Gap
1. TSH ; Thyroid Stimulating Hormone
Standard upper limit: 4.0–5.0 mIU/L
Evidence-based fertility target: Below 2.5 mIU/L
Most laboratories will not flag your TSH until it exceeds 4.0 mIU/L. But the American Thyroid Association and multiple fertility societies now recommend TSH below 2.5 mIU/L as the target for women trying to conceive a threshold that a significant proportion of women with "normal" TSH do not meet.
The research is clear: TSH values between 2.5 and 4.0 are associated with higher rates of anovulation, elevated androgens, impaired implantation, and longer time to conception. These are not marginal differences. They are clinically meaningful.
What this means for you: A TSH of 3.2 will not raise a flag. But by fertility research standards, it warrants attention especially if you also experience fatigue, cold sensitivity, hair thinning, or irregular periods.
2. Ferritin; Iron Storage
Standard lower limit: 10–20 µg/L
Evidence-based fertility target: Above 70–100 µg/L
Ferritin is routinely tested and routinely misinterpreted. A result of 18 µg/L sits within the normal range and will be reported as such. But research published in Fertility and Sterility links ferritin levels below 30–40 µg/L to significantly poorer IVF outcomes, including reduced egg quality and lower fertilisation rates.
Ferritin is not merely an iron storage protein. It is essential for DNA synthesis, mitochondrial energy production, and the conversion of inactive T4 to active T3 thyroid hormone. Low ferritin quietly compounds thyroid dysfunction, disrupts follicular development, and undermines the very processes that conception depends on, all while your results appear unremarkable.
What this means for you: If your ferritin is 18 and you've been told your iron is fine, it is worth requesting a full iron panel and asking specifically where your level sits relative to fertility-optimised targets.
3. Vitamin D
Standard sufficiency threshold: Above 50 nmol/L
Evidence-based fertility target: 100–150 nmol/L
Vitamin D is far more than a bone health marker. Receptors for vitamin D are found in the ovaries, uterus, and placenta, it plays a direct role in follicular development, implantation, and early pregnancy support. A comprehensive meta-analysis in Human Reproduction Update found that women with vitamin D levels above 75 nmol/L had significantly higher clinical pregnancy and live birth rates in IVF cycles than those below this threshold.
Yet most laboratories consider anything above 50 nmol/L sufficient. Women living in northern climates including Canada frequently sit between 40 and 70 nmol/L through much of the year, technically sufficient, functionally suboptimal.
What this means for you: A vitamin D result of 55 nmol/L will not prompt concern. But for a woman trying to conceive, it represents meaningful room for improvement and targeted supplementation is safe, inexpensive, and evidence-supported.
4. Fasting Insulin
Standard upper limit: Up to 25 mIU/L (often not tested at all)
Evidence-based fertility target:Below 8 mIU/L
This is the marker most likely to be missing from your results entirely and one of the most important for fertility.
Fasting insulin is frequently excluded from standard panels. When it is measured, results below 25 mIU/L are typically considered acceptable. But research by Legro and colleagues demonstrated that fasting insulin above 10–12 mIU/L is independently associated with ovulatory dysfunction even in women without a PCOS diagnosis and with completely normal fasting glucose.
Subclinical insulin resistance drives androgen excess, disrupts follicular maturation, impairs implantation, and raises miscarriage risk. It does so without triggering a single abnormal result on a standard panel. The evidence-based optimal target is below 8 mIU/L — a threshold that places a fasting insulin of 14 firmly in the territory worth addressing.
What this means for you: If fasting insulin has never appeared on your bloodwork, it is worth asking for it specifically. It is one of the most modifiable markers in fertility health, and dietary intervention can shift it meaningfully within weeks.
The Gap Is Structural Not Personal
The distance between normal and optimal is not the result of negligent doctors or a broken system. It is a structural feature of how medicine is designed. Conventional care is built to identify and treat disease. It is not built to optimise function in people who fall just inside the disease-free threshold.
Functional medicine fills that space. It interprets results in the context of your goals not a statistical average and uses research-backed targets to identify what is worth addressing before it becomes a diagnosis.
For women trying to conceive, this reframe is not a luxury. It is often what finally makes the difference.
What next?
If any of these markers resonate with your own results, here is where to start:
Ask for your actual numbers. Not normal or abnormal, the specific value. You are entitled to this.
Request the markers that may be missing. Fasting insulin in particular is frequently omitted. Ask for it by name.
Compare against fertility-optimised targets.Use the thresholds outlined above as a starting point for an informed conversation with your practitioner.
Know that suboptimal is not irreversible. Every marker discussed here is modifiable through nutrition, targeted supplementation, and lifestyle intervention. The goal is not perfection. It is giving your body the conditions it needs.
You do not have to accept "everything looks fine"if it does not match how you feel or what you are experiencing. The research supports asking more and so do I.
References
-Alexander EK et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum. Thyroid. 2017.
- Somigliana E et al. Serum ferritin at the time of ovarian stimulation and IVF outcome in women with endometriosis. Fertil Steril.2018.
- Chu J et al. The role of vitamin D in successful implantation and pregnancy following assisted reproductive treatment. Hum Reprod Update. 2019.
- Legro RS et al. Fasting glucose to insulin ratio is a useful measure of insulin sensitivity in women with polycystic ovary syndrome. J Clin Endocrinol Metab. 1998.
Dr. Rose Ngandalo is a Medical Doctor specialising in Functional and Integrative Medicine, with a focus on metabolic and fertility health.
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