Which blood tests are worth asking for before you conceive?

There's a long list circulating of labs you "must" have before trying. Some are genuinely useful, some are reasonable to ask for, and some cost money without changing anything. Here's the honest sorting.

Worth having

• TSH. Thyroid problems are common, easy to find and treatable. What the numbers mean →
• Complete blood count, with ferritin. A normal blood count can hide low iron stores: you can have plenty of red cells and still be running on empty. Ferritin is the number that shows it, and low iron is worth correcting before pregnancy, when demand roughly doubles.
• Vitamin D. What the evidence supports →
• Rubella and varicella immunity. Both vaccines are live, so they can't be given in pregnancy. This is the moment to find out.
• Blood type and antibody screen. Matters if you bleed or miscarry.

Reasonable to ask for, in the right situation

• Celiac screening (tTG-IgA, with total IgA) if you've had unexplained infertility, recurrent loss, iron deficiency that won't resolve, or gut symptoms. Celiac disease affects around 1% of people, is often silent, and several studies have found it more common in unexplained infertility. You must still be eating gluten for the test to mean anything.
• Vitamin B12 if you're vegetarian or vegan, take metformin, or have had gastric surgery — all of which lower it. Low B12 has been associated with recurrent loss in observational studies, but there are no trials showing that supplementing it prevents miscarriage on its own. If you're deficient, fix it; it isn't a fertility treatment.
• Fasting glucose and HbA1c, especially with PCOS, a family history of diabetes, or a previous pregnancy with gestational diabetes.
• Prolactin if your cycles are irregular or you have milky discharge.

What the guidelines actually say about iron

Insufficient evidence The US Preventive Services Task Force reviewed screening for iron deficiency in pregnancy in 2024 and concluded the evidence is insufficient either way — not that it's useless, but that the trials needed to prove benefit haven't been done. Meanwhile iron deficiency is genuinely common in women who menstruate, and treating it makes people feel better. That's a fair thing to ask for, with clear eyes about what's proven.

Usually not worth your money

• Insufficient evidence IgG food sensitivity panels. They measure exposure, not intolerance, and aren't a valid test for food reactions.
• Insufficient evidence Salivary cortisol panels for "adrenal fatigue." Not a recognized diagnosis, and the testing doesn't lead anywhere.
• Insufficient evidence Broad heavy metal or mold panels without a specific exposure.
• Limited or mixed Extensive thrombophilia panels beyond antiphospholipid testing after recurrent loss. What's actually recommended →

Questions to ask

"Which of these would change what we do?" "If it comes back abnormal, what happens next?" "Is this covered, and if not, what does it cost?"