Losing Pregnancies and Nobody Knows Why? Your Genes May Hold the Answer.

Your MTHFR gene produces an enzyme that catalyzes one of the most fundamental reactions in your body: the conversion of folate into its active, usable form. This process, called methylation, happens millions of times per second in every cell. It’s not just about energy; methylation directly controls whether your cells can divide properly, repair DNA, regulate inflammation, and produce neurotransmitters.

The C677T variant, carried by roughly 40% of people with European ancestry, reduces your enzyme’s efficiency by 40 to 70%. When you’re pregnant, the demand for active folate skyrockets. Your embryo is dividing rapidly. Your homocysteine needs to be tightly regulated, or it damages the placental blood vessels and increases clotting risk. If your MTHFR enzyme is running at half speed, you cannot meet the methylation demand of early pregnancy, no matter how much folic acid you consume. Standard folic acid won’t help; your broken enzyme can’t convert it.

This often feels like a mysterious pattern: you get pregnant, there’s a heartbeat at 8 weeks, then it vanishes by week 10 or 12. Or you miscarry without ever seeing a heartbeat. Your bloodwork looks normal. But elevated homocysteine from impaired methylation has been silently damaging your placental vessels since the blastocyst stage.

Your FSHR gene encodes the receptor that sits on the surface of your ovarian follicles. FSH from your pituitary gland binds to this receptor and tells your follicles to grow and mature. The more responsive your FSHR is, the more robustly your follicles respond to stimulation. But if you carry the N680S variant, your FSHR is less sensitive to FSH. Your follicles need more hormonal signal to grow at the same rate.

The S/S genotype appears in roughly 10 to 15% of women. People with this variant often have poor ovarian response to FSH stimulation during IVF cycles, produce fewer eggs, and those eggs are often lower quality. But it affects more than IVF; even in natural cycles, your follicles may take longer to mature, your estrogen may rise more slowly, and the eggs you produce may have higher rates of chromosomal abnormality. This is a primary driver of miscarriage, because chromosomally abnormal embryos almost always miscarry, usually before you even know you’re pregnant.

You might experience longer cycles, lighter periods, or difficulty conceiving despite having ‘normal’ hormone levels on day 3 testing. The test doesn’t capture the real problem, which is not the quantity of hormones but your ovaries’ ability to hear them.

Your ESR1 gene encodes the estrogen receptor, a protein that sits inside cells throughout your uterus and responds to estrogen. During the luteal phase of your cycle, when estrogen and progesterone rise together, your endometrium becomes receptive. The lining thickens, blood vessels proliferate, immune cells organize, and the molecular signals that allow an embryo to implant are turned on. Your estrogen receptors are the maestro conducting this orchestra.

The PvuII and XbaI variants of ESR1 affect how sensitive your endometrial cells are to estrogen. Roughly 40% of women carry at least one of these variants. When you have certain ESR1 variants, your endometrium becomes receptive at a different time in your cycle than in women without the variant, or it may never reach full receptivity at all. An embryo that arrives at your uterus on day 7 but your endometrium doesn’t become receptive until day 9 cannot implant. The timing is off.

You might have a perfectly normal-looking uterus on ultrasound, normal hormone levels, a normal luteal phase, and still not get pregnant. Or you get pregnant but miscarry early because implantation was weak and placentation never fully stabilized. ESR1 variants are invisible on standard testing but profoundly affect your fertility.

Your CFTR gene produces a protein that regulates chloride and water transport across cell membranes. Most people think of CFTR only in the context of cystic fibrosis, which requires two mutated copies. But carriers, with just one variant, face a different reproductive issue. In men, CFTR variants can lead to congenital bilateral absence of the vas deferens (CBAVD), the tubes that carry sperm from the testes to the urethra.

Roughly 1 in 25 people of European ancestry carry a CFTR variant. In men, certain variants prevent the vas deferens from developing properly, resulting in azoospermia (no sperm in the ejaculate) or severe oligospermia (very few sperm). Standard semen analysis will show the problem, but the cause is often not identified because CFTR variants are not routinely tested in fertility workups. A man with a CFTR variant will have a normal sperm count until suddenly he doesn’t; his reproductive anatomy is structurally missing. This is obstructive azoospermia, not hormonal infertility, and it requires a different approach.

If you and your partner are struggling to conceive and his semen analysis shows very low or absent sperm, CFTR testing should be part of the workup. If he carries a variant, options include surgical sperm retrieval followed by IVF, or genetic counseling if CFTR variants run in his family.

Your DAZL gene and its family members (collectively called azoospermia factor, or AZF) sit on the Y chromosome and encode proteins absolutely required for spermatogenesis, the process of turning immature cells into mature sperm. Without these genes, sperm cannot form. These are not subtle regulatory genes; they’re critical infrastructure. Deletions in AZFa, AZFb, or AZFc regions of the Y chromosome eliminate entire stretches of genetic code needed for sperm production.

AZF deletions occur in roughly 1 in 2,000 to 3,000 men with infertility. If a man carries a deletion, he will have azoospermia (no sperm) or severe oligospermia. The larger the deletion, the more severe the phenotype. A man with an AZFc deletion might have some sperm production but at very low levels. A man with an AZFa deletion typically has zero sperm. This is not a hormone problem and cannot be fixed with testosterone or FSH; the genes required to make sperm are physically absent.

If your partner has been diagnosed with azoospermia or very low sperm count, Y-chromosome microdeletion testing should be done. If a deletion is found, the couple needs to know that natural conception is not possible, but sperm retrieval and IVF with ICSI may work depending on which region is deleted.

Your AR gene encodes the androgen receptor, the protein that testosterone and DHT bind to in order to exert their effects. Every male cell with an androgen receptor listens to testosterone through this receptor. In the testis, androgen receptor signaling is absolutely essential for spermatogenesis. Without proper androgen receptor function, sperm cannot be produced.

The AR gene contains a stretch of CAG repeats; the number of repeats varies between individuals. Longer CAG repeat lengths correspond to lower androgen receptor sensitivity. If you have a normal-range repeat length, your testis responds robustly to testosterone and makes abundant sperm. If you have a longer repeat length, your androgen receptor is less sensitive, your testis receives a weaker signal, and sperm production drops. You can have normal testosterone levels but if your androgen receptor is less responsive, your spermatogenesis will be impaired. This is why some men with low sperm count also have normal or near-normal testosterone.

This is especially relevant if your partner has been diagnosed with oligospermia and testosterone supplementation hasn’t helped, or if he’s being treated with HCG to boost testosterone but sperm production isn’t improving. The problem may not be testosterone quantity but androgen receptor sensitivity.