Vitamin B12 appears on most “best supplements for TTC” lists and in many prenatal and cycle-support formulas. Do you need extra, and what should you check on a label before you buy? This guide sticks to published intake guidance so you can decide with your doctor.
This is educational, not medical advice. For the full overview of options, see fertility supplements to get pregnant.
1. What vitamin B12 is
Vitamin B12 (cobalamin) is a water-soluble vitamin involved in red blood cell formation, nerve function and DNA synthesis. It works alongside folate, which is why the two are often discussed together on preconception checklists. It is found mainly in animal foods (meat, fish, eggs, dairy) and in fortified foods.
2. Intake guidance to know (NIH Office of Dietary Supplements)
| Group | Adult guidance | Upper limit |
|---|---|---|
| Adults (19+) | RDA is 2.4 mcg/day | No upper level has been set for B12 |
| Pregnancy | RDA is 2.6 mcg/day | No upper level has been set |
“No upper level” does not mean “more is better” — it means the NIH found no established harm at high intakes from food and supplements. Check current figures on the NIH ODS site and confirm your own targets with your doctor.
3. What the research does and does not show
- Fertility outcomes: there is no large, high-quality trial showing that extra B12 raises the chance of pregnancy in people who already get enough.
- Deficiency: low B12 is a recognized nutrition issue, and a doctor can check it with a blood test. Correcting a confirmed low level is care guided by a result, not a guess.
- Preconception nutrition: B12 and folate status are part of standard preconception nutrition discussions; ask your provider which tests make sense for you.
If your cycle is the real concern, start with a work-up — see ovulation cycle tracking.
4. Who may want to ask a doctor about B12 first
- Vegan or vegetarian diets: B12 comes mostly from animal foods — read vegan and vegetarian TTC supplement checks.
- Metformin or acid-reducing medicines: some medicines can affect B12 absorption — ask your doctor or pharmacist whether testing makes sense.
- Digestive or absorption conditions: ask before assuming a standard supplement is enough.
- In an IVF or IUI cycle: follow your clinic’s protocol — read what to ask your clinic.
5. Buying B12: 5 quick checks
- Add up the total. List every product you take — prenatal, multivitamin, TTC formula — and the mcg of B12 in each.
- Form: labels list cyanocobalamin, methylcobalamin or others; ask your doctor if the form matters for you.
- Amount in mcg clearly listed, not hidden inside a proprietary blend.
- Third-party testing (USP, NSF or a certificate of analysis). In Canada, look for an NPN.
- Ask for the full label of any AGO product you are considering — the care team shares it on request so you can compare per-serving amounts.
Results vary and no supplement guarantees pregnancy. Bring your labels to your next visit — our doctor checklist helps, and the methylfolate vs folic acid guide covers its partner nutrient. Get a free personalized plan.
FAQ
Should I take vitamin B12 when trying to conceive?
B12 is an everyday nutrient, and many people get it from food and from a prenatal or TTC formula. Whether to add more is a question for your doctor, ideally based on your diet and any test results.
How much B12 do adults need?
The NIH lists an RDA of 2.4 mcg/day for adults and 2.6 mcg/day during pregnancy. Confirm your own needs with your doctor.
Is there an upper limit for vitamin B12?
The NIH has not set an upper level for B12, but that does not mean higher amounts are better. Count every product you take.
Is B12 already in AGO Mom?
Ask the AGO care team for the product label — they send it on request so you can see what is in each serving and avoid doubling up with other products.
Does he need B12 too?
Men have the same intake guidance. There is limited evidence for a fertility benefit from extra amounts, so ask his doctor before adding it.