What fertility tests should I ask for?

What fertility tests should I ask for?

One of the most common things I hear from women who come to me is some version of this: "My GP said everything looks normal, but I still cannot get pregnant." And I understand exactly how confusing and demoralising that feels. Because here is something that most people are never told: the standard blood tests your GP orders are designed to identify serious disease, not to optimise fertility. Normal on a standard panel does not mean optimal for conception.

This is where my work begins. When I assess a client's fertility from a nutritional standpoint, I am looking at a completely different set of questions. Not just whether a number sits within an acceptable range, but whether it is at the level your body needs to conceive, sustain a pregnancy, and thrive. Those two things are very different, and the gap between them is often where the answers are hiding.

Let me walk you through the tests I consider most important, and why each one matters for your fertility.

Hormone tests: understanding your cycle from the inside

These are the tests most people are familiar with, and they form an important foundation. FSH, or follicle-stimulating hormone, is best tested on day two or three of your cycle and gives an indication of how hard your body is working to stimulate egg development. Elevated FSH can be a sign of reduced ovarian reserve. LH, or luteinising hormone, tested at the beginning of your cycle, helps identify hormonal imbalances including PCOS, and when tested mid-cycle it confirms whether ovulation is occurring. Oestradiol, tested alongside FSH on day two or three, helps give a fuller picture of ovarian function. Progesterone, tested around day 21 of a 28-day cycle, tells us whether ovulation has actually occurred and whether your luteal phase is strong enough to support implantation. Low progesterone is one of the most commonly missed contributors to conception difficulties and early pregnancy loss.

AMH, or anti-Müllerian hormone, is one of the most useful fertility markers available to us. It reflects your ovarian reserve, or how many eggs remain, and can be tested at any point in your cycle. It does not tell us about egg quality, but it gives important context for how your body is likely to respond to fertility treatments and helps shape the urgency and direction of your plan.

Prolactin is worth checking too. Elevated prolactin, which is produced by the pituitary gland, can suppress ovulation and is a treatable cause of cycle disruption that is frequently overlooked.

Androgens including testosterone and DHEAS are important if there is any suspicion of PCOS, excess hair growth, acne, or irregular cycles. An elevated free androgen index is a key marker in PCOS diagnosis.

Thyroid function: one of the most critical and most missed

I cannot emphasise this one enough. Thyroid health is deeply intertwined with fertility, and yet a standard GP panel will only check TSH. TSH alone is not enough. Hypothyroidism, Hashimoto's thyroiditis, and even subclinical thyroid dysfunction can all disrupt ovulation, impair implantation, increase miscarriage risk, and affect the neurological development of a baby in early pregnancy. Research has confirmed that thyroid antibodies negatively affect embryo quality and are associated with early pregnancy loss.

When I am working with a client, I want to see the full thyroid picture including TSH, free T3, free T4, and thyroid antibodies (anti-TPO and anti-thyroglobulin). Many women discover that despite a TSH within the standard reference range, their thyroid is not functioning at the level their fertility requires. This is a completely addressable issue when it is identified.

Nutritional markers: the layer that standard testing almost always misses

This is the area I find most rewarding to work in, because it is where we so often find the missing pieces of the puzzle. A comprehensive review of current evidence published in 2024 confirmed that deficiencies in key micronutrients including vitamins D, E, C, and B12, as well as minerals including zinc, iron, selenium, and magnesium, directly lead to hormonal imbalances, impaired egg development, and poor pregnancy outcomes. These deficiencies are extremely common, and extremely addressable when properly identified.

Vitamin D is one of the most consistently deficient nutrients I see in clinical practice, and one of the most significant for fertility. Research comparing infertile and fertile women has found meaningful differences in vitamin D levels between the two groups. Fertility clinics often prefer vitamin D levels to sit between 75 and 100 nmol/L, which is considerably higher than the standard reference range. Many women sitting in the "normal" range are still well below what their reproductive system needs.

Iron and ferritin are essential for oxygen delivery to the reproductive organs, for healthy ovulation, and for early pregnancy development. Low ferritin was identified in 45.5% of infertile patients in a study comparing infertile and fertile women, making it one of the most commonly deficient markers I see. Standard panels may show haemoglobin within range while ferritin, the stored form of iron, is critically low.

Vitamin B12 is another marker I check carefully, particularly in women who eat a largely plant-based diet or take metformin. B12 deficiency can cause blood clotting abnormalities that increase miscarriage risk and may prevent a fertilised embryo from implanting properly. It also works in close partnership with folate, and the two need to be in balance to function correctly.

Folate and homocysteine are assessed together in my practice. Homocysteine is an amino acid that rises when folate, B12, or B6 are insufficient. Elevated homocysteine disrupts follicular growth, oocyte quality, embryo development, and endometrial receptivity, increasing the risk of implantation failure, miscarriage, and pregnancy complications. It is a highly modifiable factor, and one that is rarely tested in standard fertility workups.

Zinc levels deserve attention in both female and male fertility. In women, zinc deficiency is linked to increased pregnancy loss, poor hormonal function, and compromised egg quality. Research has found that infertile women have significantly lower serum zinc levels compared to fertile women, and that women experiencing threatened miscarriage had zinc levels 35.7% lower than healthy pregnant women.

Selenium supports thyroid function, protects eggs from oxidative damage, and is essential for healthy gametogenesis. Lower selenium concentrations in serum and follicular fluid are associated with increased infertility rates and are something I assess as part of a thorough nutritional workup.

Genetic markers: understanding how your body processes nutrients

MTHFR gene variants are present in approximately 40% of the population and affect the body's ability to convert synthetic folic acid into the active form of folate the body can actually use. Women with MTHFR variants who are taking standard folic acid supplements may not be getting the folate protection they think they are, which has implications for neural tube defect prevention, homocysteine metabolism, and miscarriage risk. Knowing your MTHFR status allows us to personalise your supplementation precisely.

Gut health and the microbiome

This is an area that standard fertility investigations do not touch at all, and yet the evidence linking gut health to hormonal metabolism, immune function, nutrient absorption, and reproductive outcomes is growing rapidly. A comprehensive stool analysis can reveal dysbiosis, gut infections, inflammatory patterns, and digestive insufficiencies that are quietly affecting your fertility from the inside. The vaginal microbiome is also emerging as an important factor in implantation success, and is something I consider when the picture calls for it.

For your partner too

Fertility is a two-person equation, and sperm quality accounts for a significant proportion of conception challenges. A full semen analysis is the starting point, but the nutritional markers that affect sperm health, including zinc, selenium, CoQ10, vitamin D, folate, and antioxidant status, are just as worth assessing in a male partner as they are in you.

The difference between testing and truly understanding

What I do in my practice is not just order tests and hand you a printout. It is to look at all of these markers together, in the context of your full health history, your symptoms, your cycle, and your goals, and understand what the picture is telling us. A result that sits within a standard reference range may still be inadequate for your fertility. A result that looks borderline may be the key to everything.

If you have been told everything is normal and you still cannot conceive, or if you have simply never had a thorough nutritional assessment, this is where I would start. Because the answers are often there in the data. You just need someone who knows what to look for.

Sources: PMC 2024 (nutritional deficiencies and subfertility, comprehensive review); PMC 2023 (thyroid hormones, vitamins and microelements in female infertility); Frontiers in Nutrition 2025 (MTHFR, homocysteine and vitamin D in infertile patients); MDPI Nutrients 2025 (homocysteine and fertility, literature review); Dr Jolene Brighten 2024 (lab work when trying to conceive); Levy Health (fertility blood testing and cycle timing); Progyny (fertility blood tests overview); Loma Linda University Center for Fertility; Nutritionist Resource (key nutrition blood tests for fertility); WeNatal (nutrients and miscarriage risk).