Getting pregnant with hypothyroidism is absolutely possible, but it usually requires getting your thyroid levels well controlled before you start trying. An underactive thyroid disrupts ovulation, raises the risk of miscarriage, and can interfere with fertility in ways that go beyond just “feeling tired.” The good news is that most of these effects are reversible once your thyroid hormone levels are optimized.
How Hypothyroidism Disrupts Fertility
Your thyroid hormones play a surprisingly central role in reproduction. When thyroid levels drop too low, your brain produces more of a hormone called TRH to compensate. TRH also stimulates prolactin, the same hormone responsible for breast milk production. Elevated prolactin suppresses the chain of signals your brain sends to your ovaries to trigger ovulation. So even if your periods seem somewhat regular, you may not be ovulating consistently.
The disruption goes deeper than ovulation timing. Thyroid hormones directly support the ovarian cells that nurture developing eggs, helping them respond to FSH (the hormone that drives follicle growth). In a hypothyroid state, those cells become less responsive to FSH, which can mean eggs don’t mature properly or follicles stall before reaching the point of release. In one study, both LH and FSH were suppressed in hypothyroid women and increased once thyroid levels returned to normal.
Your TSH Target Before Conceiving
There’s been a lot of conflicting advice about the “ideal” TSH for getting pregnant. For years, many practitioners aimed for a TSH below 2.5 before conception. The American Society for Reproductive Medicine has since clarified that a TSH between 2.5 and 4.0 is not associated with an increased risk of miscarriage. Their current recommendation is to use standard age-based lab reference ranges rather than stricter pregnancy-specific cutoffs while you’re still trying to conceive.
When your lab doesn’t provide age-specific ranges, the general upper limit is 4.12 for nonpregnant patients and those attempting pregnancy. Once you become pregnant, that threshold drops by about 0.5 in the first trimester. The practical takeaway: you don’t necessarily need to push your TSH below 2.5 before trying, but you do need to be within normal range and have a plan for adjusting quickly once pregnant.
Miscarriage Risk With Elevated TSH
The stakes of uncontrolled hypothyroidism become clearer once conception happens. Women with a TSH between 4.5 and 10 during early pregnancy have 1.8 times the risk of miscarriage compared to women with a TSH between 0.2 and 2.5. For those with a TSH above 10, that risk jumps to nearly 4 times higher. This is why preconception thyroid management matters so much: you want your levels stable before pregnancy, not scrambling to correct them after.
Adjusting Medication Once Pregnant
If you’re already on thyroid hormone replacement, your dose will likely need to increase as soon as you get a positive test. The standard recommendation is to raise your dose by 20 to 30 percent immediately upon confirming pregnancy. A simple way to do this: take two extra doses per week on top of your usual daily pill. This prevents a gap in coverage during the critical early weeks when your baby’s brain development depends heavily on your thyroid hormones.
Ideally, you’ll have discussed this plan with your provider before you start trying. Preconception counseling for women with known hypothyroidism should cover exactly when and how to adjust, so you’re not waiting for an appointment while your levels drift. If pregnancy is planned, thyroid screening should happen before conception or as soon as pregnancy is suspected.
Thyroid Antibodies Add a Separate Risk
Hashimoto’s thyroiditis, the autoimmune condition behind most hypothyroidism cases, introduces an additional layer of complexity. Even when your TSH and thyroid hormone levels are perfectly normal, the presence of thyroid peroxidase (TPO) antibodies independently raises the risk of early pregnancy loss. In a study of over 1,200 women undergoing IVF, those who were euthyroid (normal thyroid levels) but had positive TPO antibodies had a miscarriage rate of 15% compared to 8.7% in women without the antibodies. The risk of a biochemical pregnancy, where a test briefly turns positive but the pregnancy doesn’t progress, was also roughly double.
This means that even if your thyroid numbers look good on paper, it’s worth knowing your antibody status. About 12% of women in that study tested positive for TPO antibodies. If you have Hashimoto’s, your provider may monitor you more closely in early pregnancy or consider treatment strategies beyond standard hormone replacement.
When Your Partner Has Hypothyroidism
Thyroid problems aren’t exclusively a female fertility issue. In men, low thyroid hormones reduce testosterone and impair sperm production at a fundamental level. The thyroid hormone T3 activates gene transcription in testicular cells and stimulates the support cells responsible for producing and maturing sperm. Without adequate T3, sperm count, motility, and the percentage of normally shaped sperm all decline significantly.
Hypothyroidism also creates oxidative stress within testicular tissue, damaging sperm cells directly. Men with untreated hypothyroidism show lower levels of protective antioxidant enzymes and higher levels of damaged proteins in their reproductive tissue. If you’ve been struggling to conceive and your partner hasn’t had thyroid testing, it’s a worthwhile step. Treating male hypothyroidism can improve sperm quality substantially.
Nutrition That Supports Thyroid Function
Two nutrients deserve specific attention when you’re trying to conceive with a thyroid condition: iodine and selenium. Your thyroid needs iodine as the raw material for producing thyroid hormones, and selenium supports the enzymes that convert those hormones into their active form. The recommended daily intake of iodine for women in the preconception period is 150 micrograms per day, increasing to 250 micrograms once pregnant or breastfeeding.
Selenium is particularly relevant for women with Hashimoto’s. There is active research into whether supplementing with around 100 micrograms of selenium daily alongside iodine may help reduce the autoimmune thyroid flare-ups that sometimes occur during pregnancy. Good dietary sources of selenium include Brazil nuts (just one or two per day can meet your needs), seafood, eggs, and poultry. For iodine, dairy products, seaweed, iodized salt, and fish are the most reliable sources. If you’re on a restricted diet, a prenatal vitamin with iodine can help close the gap.
A Practical Timeline for Trying
If you’ve recently been diagnosed or your levels aren’t yet stable, give yourself at least a few months of consistent treatment before actively trying. Thyroid medication typically takes 4 to 6 weeks to reach its full effect after a dose change, and you may need more than one adjustment to hit your target range. A reasonable approach is to confirm your TSH is within normal range on at least one blood test before conceiving, then retest early in pregnancy to guide any dose changes.
Once you’re trying, treat a positive pregnancy test as a signal to act immediately on your medication plan. The first trimester is when thyroid demand surges and when the risk from inadequate levels is highest. Having a clear protocol already in place, knowing exactly how many extra pills to take and when to get blood drawn, removes the guesswork during a time when speed matters.