Taking Folic Acid and Still Worried. Here's Why Your Genes Matter.

Your MTHFR gene codes for the methylenetetrahydrofolate reductase enzyme, which is responsible for one of the most critical steps in your metabolism: converting dietary folate and supplemental folic acid into methylfolate, the form your cells actually use for DNA synthesis, repair, and methylation reactions.

Roughly 40 percent of people of European ancestry carry at least one copy of the C677T variant. This variant reduces enzyme efficiency by 40 to 70 percent. If you’re homozygous (two copies), the reduction is more severe. The A1298C variant has milder effects but often compounds C677T if you carry both.

During pregnancy, the demand for methylfolate increases dramatically. Your baby’s neural tube is closing in the first 28 days of gestation, before many women even know they’re pregnant. If your cells are folate-depleted due to MTHFR dysfunction, you face higher risk of neural tube defects, miscarriage, and impaired fetal development. Elevated homocysteine, a direct consequence of folate insufficiency, is itself a miscarriage risk factor.

Your VDR gene codes for the vitamin D receptor, a protein that sits on your cell surfaces and tells your cells what to do when vitamin D is present. It’s not about how much vitamin D you consume or how much sunlight you get; it’s about whether your cells can actually use that vitamin D when it arrives.

Approximately 30 to 50 percent of people carry VDR variants like BsmI or FokI that reduce receptor sensitivity. This means your cells require more vitamin D to trigger the same biological response as someone with the common variant. You might have normal or even high vitamin D blood levels and still be functionally deficient at the cellular level.

In pregnancy, vitamin D is critical for implantation, immune tolerance (preventing miscarriage), calcium absorption for fetal bone development, and reducing miscarriage risk. Women with VDR variants who don’t optimize their vitamin D levels face higher rates of implantation failure, pregnancy loss, and preeclampsia. Low vitamin D is also associated with poor ovulation and reduced fertility in the preconception phase.

Your COMT gene codes for catechol-O-methyltransferase, an enzyme that inactivates estrogen and the stress neurotransmitters dopamine and norepinephrine. The Val158Met variant is the most common, and it dramatically affects how fast your body clears estrogen.

Approximately 25 percent of people of European ancestry are homozygous for the slow variant (Met/Met). Slow COMT means estrogen accumulates in your system longer, and you can develop functionally elevated estrogen even with normal blood levels. This is not obvious from standard hormone panels.

Elevated estrogen drives endometriosis, PCOS, heavy periods, and compromised egg quality. During the luteal phase of your cycle, you need progesterone to rise and estrogen to fall; if your estrogen clears slowly, that signal never arrives clearly, disrupting ovulation quality and luteal function. Slow COMT is also associated with estrogen-dependent breast tissue sensitivity and increased miscarriage risk when estrogen feedback is disrupted.

Your FSHR gene codes for the follicle-stimulating hormone receptor, which sits on your ovarian cells and responds to FSH signaling during your menstrual cycle. FSH recruits and matures egg-containing follicles; without clear FSH receptor function, follicle recruitment is poor.

The N680S variant (rs6166) occurs in approximately 10 to 15 percent of women. Women with the S/S genotype have lower FSH receptor sensitivity and require higher FSH levels to recruit and mature eggs. This shows up as high FSH despite normal or low ovarian reserve, or as unexpectedly poor response to ovarian stimulation during IVF cycles.

Poor FSH sensitivity doesn’t mean you can’t conceive, but it means your ovaries work harder to respond. Your natural cycles may have fewer eggs recruited, lower egg quality, or delayed ovulation. In IVF, you require higher gonadotropin doses. More broadly, you may face diminished ovarian reserve or premature ovarian aging compared to women with typical FSH receptor sensitivity.

Your HFE gene codes for the hemochromatosis protein, which regulates hepcidin, the hormone that controls iron absorption. Too much hepcidin means less iron absorbed; too little means iron accumulates. The balance is critical because both iron deficiency and iron excess harm fertility and fetal development.

The H63D variant occurs in approximately 15 to 20 percent of people of European ancestry. H63D carriers often experience mild iron dysregulation; some absorb iron less efficiently, while others accumulate it. The C282Y variant causes full iron overload (hemochromatosis) and is less common but more severe.

During pregnancy, iron demands double because your blood volume expands and you’re building your baby’s iron stores. If you have the H63D variant, you may absorb iron poorly from food and supplements, leading to gestational anemia, reduced placental function, and intrauterine growth restriction. Conversely, if your variant causes iron accumulation, excess iron generates oxidative stress that damages eggs and placental tissue, increasing miscarriage risk. You need to know which direction your iron regulation is dysregulated so you can correct it.

Your SOD2 gene codes for superoxide dismutase 2, a mitochondrial enzyme that neutralizes reactive oxygen species and protects your cells from oxidative damage. Mitochondria generate energy for your eggs, your implanting embryo, and your developing placenta; if they’re damaged by oxidative stress, fertility and pregnancy outcomes suffer.

The Ala16Val variant (rs4880) is common in the population. The Val allele is associated with lower SOD2 activity and reduced mitochondrial protection, meaning your cells accumulate oxidative damage more readily. This is especially critical in eggs, where mitochondrial dysfunction directly impairs egg quality and fertilization rates.

Oxidative stress in eggs accelerates aging, reduces fertility, and increases miscarriage risk. Oxidative stress in the developing placenta impairs nutrient transfer and is linked to preeclampsia, gestational diabetes, and intrauterine growth restriction. Women with SOD2 variants who don’t aggressively manage oxidative stress face lower conception rates, higher miscarriage rates, and worse pregnancy outcomes if they do conceive.