Fourteen numbers, one question

Kavya, 31, came in with a printout from a "fertility panel" she had ordered online. Fourteen markers, each with a reference range, three flagged in red. She had also been charting her temperature for four months. Her question was simple. "Which of these tells me whether I'm fertile?"

The honest answer is that none of them can, on its own. Biomarkers are genuinely useful in fertility care, but they work best as answers to specific questions, not as a fertility score. This piece sorts out which marker answers which question, and where the limits are.

What a biomarker is, and what it isn't

A biomarker is any measurable sign of a biological state: a hormone level, a physical change, a protein, a gene. In reproductive medicine, biomarkers do four jobs. They mark a stage of development or a disease, show an effect, show an exposure, or flag susceptibility.

One thing worth knowing from the research literature: reproductive biomarkers are still a young field [1]. Many candidates need extensive testing and validation before they earn a place in routine care. In practice, that means most markers on a panel are better at explaining a problem you already have than at predicting who will conceive.

Biomarkers you can observe yourself

Your cycle produces signs long before any blood is drawn. Cervical mucus becomes wetter and more slippery as estrogen rises. Basal body temperature, your resting morning temperature, rises after ovulation as progesterone increases. Urine tests detect the LH surge. Serial ultrasound scans follow a follicle, and its collapse after the egg is released is strong evidence that ovulation happened.

Two practical points. A temperature rise confirms ovulation after the fact. It cannot predict it. And a charted cycle gives your doctor something better than a guess about where you were in your cycle when blood was drawn, which matters because several hormone tests only make sense on specific cycle days.

What this means for you: if you are charting, bring the chart to your appointment. It makes every blood test easier to read.

Which fertility blood tests answer which question?

Marker

What it helps answer

What it can't tell you

AMH

How many follicles remain (ovarian reserve). Likely response to IVF stimulation

Egg quality. Your chance of conceiving naturally

FSH and estradiol (early cycle)

How the brain and ovaries are communicating

Fertility on its own. High FSH did not lower conception rates in one large cohort

LH

Timing of the ovulation surge

Whether an egg was actually released

Mid-luteal progesterone

Whether ovulation occurred

Anything, if drawn on the wrong cycle day

TSH (with free T4, antibodies where indicated)

Thyroid problems that affect cycles and pregnancy

Fertility potential. It screens for one treatable cause

Prolactin

A cause of irregular or missed periods

Routine need. It is not advised as a standard test when cycles are regular

Testosterone, SHBG, fasting glucose or insulin, HbA1c

The hormonal and metabolic picture in PMOS (formerly PCOS)

Day-to-day glucose swings, since HbA1c reflects a 2 to 3 month average

Vitamin D, ferritin, B12, folate

Deficiencies that are easy to correct

Fertility. These are nutrition markers, not fertility tests

CA-125 [12]

Can add to suspicion of endometriosis, but is not a diagnostic test on its own

Rules endometriosis out when normal. It also rises with fibroids and early pregnancy

AMH: the most misunderstood number

AMH reflects ovarian reserve, meaning how many follicles remain. It does not measure egg quality. It is a good predictor of how the ovaries will respond to stimulation in IVF. Its ability to predict who will have a baby is poor, even in IVF [6].

For natural conception, the evidence is consistent. In a US cohort of 750 women aged 30 to 44 with no history of infertility, women with low AMH (below 0.7 ng/mL) had a 65 percent chance of conceiving within 6 cycles, against 62 percent for women with normal AMH. FSH, inhibin B, and urinary FSH told the same story [2]. A meta-analysis of 11 studies and 4,388 women concluded that AMH has poor predictive value for natural pregnancy [3]. A Danish register study of 43,269 women found a positive association between AMH and pregnancy but a poor ability to predict it [4].

Not every study agrees. One cohort of 3,150 women linked AMH levels to time to pregnancy, so low AMH is not meaningless [5]. But it is a modest signal, not a verdict. ESHRE advises that in women with regular cycles, ovarian reserve testing is not needed to find a cause or to predict natural conception [8]. ASRM likewise says these tests cannot predict failure to conceive and should not be used to deny treatment [9].

A few interpretation points follow from this.

  • AMH usually runs lower while you are on hormonal contraception, so the timing of the test matters [7].

  • A high AMH is not automatically good news. It is often raised in PMOS.

  • AMH earns its place in planning. It informs IVF protocols and conversations about egg freezing, where the question is how much time and how many eggs to plan for.

What this means for you: a low AMH is information for planning, not a forecast. If your cycles are regular and you are trying to conceive naturally, it should not be what decides your next step.

Biomarkers for men

Semen analysis is the main test. It measures concentration, motility, and morphology. The WHO lower reference limits are 16 million sperm per mL, or 39 million in the whole ejaculate. These are reference limits, not fertility cut-offs. Men below them can father children, and men above them can struggle.

Inhibin B and FSH reflect how well sperm are being made. In one study, both correlated with sperm count, but the sperm concentration itself was the best predictor of natural fertilization, and pregnancy occurred in some men with very low inhibin B [11]. Sperm DNA fragmentation testing is not part of routine first-line evaluation under either AUA/ASRM or ESHRE guidance, though it may be considered in selected cases such as recurrent pregnancy loss [10].

Promising, but not ready for routine use

Researchers are studying implantation markers such as glycodelin and leukemia inhibitory factor, circulating microRNAs for PMOS, and seminal plasma proteins that may help diagnose the cause of azoospermia. Vaginal and semen microbiome testing is another area of interest. These are worth watching. None is a first-line test today, and a result that has not been validated can worry people without helping them.

How to use fertility blood tests sensibly

  1. Start with the question, not the panel. Irregular cycles point to ovulation, thyroid, and prolactin tests. Twelve months without conceiving points to semen analysis and tubal assessment. Thinking about egg freezing points to AMH and an ultrasound follicle count.

  2. Read every number in context. Age, cycle day, medications, and symptoms all change what a result means.

  3. Treat deficiencies, but be cautious about chasing "optimal." Correcting a true deficiency is reasonable. Pushing a normal result into a tighter range is only worth doing if a trial has shown it improves pregnancy rates.

  4. Notice who is selling the test. A doctor who orders a test for a reason is different from a bundled panel sold to everyone. More markers do not mean more answers.

The bottom line

A biomarker is a clue, not a forecast. The most useful fertility tests are the ones ordered to answer a specific question, interpreted alongside your age, your cycle, and your history. Kavya's fourteen numbers were not wrong. They were just not a question. Once we asked one, only three of them mattered.

References