Which biomarkers should we be testing for fertility?

It’s National Fertility Awareness Week, so whether you’re at the very start of your fertility journey, a couple of years down the line, prepping for IVF or gearing up to try for baby 2+, you may well be wondering what you can do to shed more light on your current fertility, or if there’s anything going on that may hinder your chances of conceiving.

As a Registered Nutritional Therapist specialising in Fertility, Natasha Evans guides us through the key tests she runs in clinic to help her clients understand their fertility, and identify any areas for optimisation.

It’s a personal preference and many people are happy to dive in and give it a go with no upfront testing.

If time and budget allows, testing upfront before you start trying to conceive can be helpful as it may pick up on things that could delay your chances of conceiving, increase risk of pregnancy complications or miscarriage, and even affect the health of the baby.

Whether you test upfront, or further down the line, there are plenty of tests available to understand your health and the factors that influence fertility. Here are some of the top biomarkers I look at with my fertility clients.

Vitamin D: Vitamin D deficiency has been associated with fertility issues, pregnancy complications, and issues with hormone and sperm production. Meanwhile, robust vitamin D levels have been associated with higher pregnancy rates. Vitamin D is also thought to play a significant role in supporting implantation process and immunological embryo-protection in the first trimester. Low vitamin D levels are also often seen in people with fertility-related conditions like PCOS or endometriosis. Low vitamin D levels can be easily addressed with supplementation.

Full Thyroid Panel: our thyroid gland regulates our metabolism, energy production, hormone levels - and more! If the thyroid isn’t functioning optimally, for example if it’s over or underactive, or there’s any autoimmunity of the thyroid, this can affect ovulation, sperm count and quality and make it difficult to conceive. Thyroid hormones also play an important part in growth, making them critical in pregnancy. Suboptimal thyroid function may contribute towards risk of miscarriage in the first trimester, or other pregnancy complications.

Sex hormones: our sex hormones regulate our fertility! They determine when or whether you ovulate, how thick the lining of the womb is, how well the lining of the womb holds in place after implantation, spermatogenesis, libido… everything! A comprehensive view of the sex hormones can be really helpful in understanding whether your reproductive system is working well. Useful markers include oestradiol, progesterone, LH, FSH, SHBG, DHEA and testosterone.

Semen analysis: the results of a semen analysis give you a good male-factor indication of your chances of conceiving, and also highlight any areas that need to be worked on. Markers of interest include sperm count, sperm concentration, motility (how well they swim) and morphology (are they the right shape?). DNA Fragmentation testing can also be very helpful, particularly in cases of unexplained infertility and recurrent miscarriage

Vaginal microbiome: emerging science has shown that the composition of your vaginal microbiome is strongly associated with fertility, implantation rates, IVF success outcomes, pregnancy outcomes - and even the health of the baby, if born via a vaginal birth. Some people might already know that they have a disrupted vaginal microbiome, for example if they regularly suffer from BV or thrush - but you can also have imbalances in the vaginal microbiome and be totally asymptomatic. The good news is that there are a number of companies now offering vaginal microbiome testing and it can be easily improved with diet, lifestyle and supplementation

Semen microbiome: whilst there is less research on the semen microbiome, we are now also starting to see patterns and links between the health of the semen microbiome and fecundity. A whole-couple approach is important in fertility and if, in a heterosexual relationship, there’s an imbalance in the vaginal microbiome, there’s likely to be something going on in the semen microbiome too.

MTHFR: this testing is often offered by fertility clinics now, but only a few years down the line, when someone is going down the assisted reproductive technology route. MTHFR is one of the genes involved in methylation, a process that affects almost all aspects of our health - including fertility. Mutations on the MTHFR gene have been associated with poorer egg quality, poorer sperm quality, an increased risk of infertility and even miscarriage. But variations on the MTHFR gene are very common - and if you know you have it, there’s plenty you can do about it. In particular, it influences which form of folate supplementation might be best for you (hint: methylfolate!)

The eagle-eyed amongst you might have noticed that AMH isn't included in this list. Anti-Müllerian Hormone (AMH) is an important marker, alongside Antral Follicle Count (AFC) in determining a medication protocol in IVF. However, now it is often being used outside of the IVF context, as an indicator of “ovarian reserve”. It’s unfortunately an imperfect metric as it can go up as well as down, and also tells you nothing about your egg quality, which is arguably more important. A recent 2024 study found that ovarian reserve, measured by AMH, did not influence natural conception; and a 2021 study concluded that “Serum AMH levels have poor predictive value for natural pregnancy”. This doesn’t mean to say that it’s never helpful: it’s certainly helpful in the IVF context and if AMH is very low, particularly for women over 40, then it may indeed be a reason to explore the IVF route sooner.

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