Preconception Supplements: The Stack That's Worth Taking

You are standing in front of a wall of bottles, or a shopping cart full of them, and you are trying to work out which preconception supplements are doing real work. Which are charging you forty pounds a month to do nothing. Most of what is marketed as a "fertility supplement" has thin evidence behind it. The honest list of compounds that earn their place in a preconception stack is short, specific, and considerably cheaper than the influencer aisle would suggest.

This post is a doctor's hierarchy of what to take, what to take only in specific situations, what to discuss with your clinician, and what to leave on the shelf. I have tried to be unhedged where the evidence is clear, and equally clear where it is not. Where a supplement deserves its own full post (folate forms, CoQ10 dose, myo-inositol for PCOS, vitamin D), I will point you to the supporting post rather than repeat the detail here.

The honest preconception supplements hierarchy

I think about preconception supplementation in four tiers. Tier 1 is for almost everyone. Tier 2 is for specific situations. Tier 3 is talk-to-your-clinician territory. The fourth group is the "no tier" pile, where I put the bottles I tell patients to put back.

Tier 1, evidence-backed for most people: Folate in any form at 400 to 800 micrograms daily. Vitamin D if your level is low, or as a sensible baseline dose if you cannot test. A basic prenatal multivitamin that contains folate, iodine, vitamin D, and ideally choline.

Tier 2, evidence-backed for specific situations: Myo-inositol for polycystic ovary syndrome (PCOS). Coenzyme Q10 (CoQ10) for advanced maternal age or diminished ovarian reserve. Additional iodine if your prenatal does not contain it. Omega-3 DHA if your diet is low in oily fish and your prenatal does not already include it.

Tier 3, mixed or thin evidence, discuss with your clinician: N-acetylcysteine (NAC). Melatonin in the context of an in vitro fertilisation (IVF) cycle. Dehydroepiandrosterone (DHEA), only under reproductive endocrinology supervision for documented diminished ovarian reserve. L-arginine. These are not on the shopping list. They are on the conversation list.

No tier: Royal jelly. Maca. Vitex or chasteberry. "Egg quality blends." "Fertility detox." Anything with a proprietary formula and no comparator trial. These are the bottles that make a preconception stack expensive without making it better.

A reasonable monthly cost for the stack that follows is roughly fifteen to forty pounds, or twenty to fifty dollars. If yours is running over a hundred a month, you are probably buying brand stories rather than active ingredients.

Tier 1: the non-negotiables

Folate, in any form

Folate is the single most evidence-backed preconception intervention in medicine, and it has been for more than thirty years. The Medical Research Council (MRC) Vitamin Study, published in The Lancet in 1991, randomised women with a prior pregnancy affected by a neural tube defect (NTD) to receive folic acid, other vitamins, both, or neither. Periconceptional folic acid reduced the recurrence of neural tube defects by approximately seventy percent.¹ The Czeizel and Dudás follow-up trial in 1992 extended the finding to first-occurrence NTDs in The New England Journal of Medicine.² The dose used was 400 to 800 micrograms of folic acid daily, started before conception. That is the dose almost every modern guideline still uses.

I tell most patients to start folate one to three months before they begin trying. Neural tube formation completes by approximately the fifth or sixth gestational week, which is the third or fourth week after conception, and is often before a pregnancy is recognised. Starting on the day of a positive test is too late for the most time-sensitive function folate has. Starting earlier is better. If you missed the ideal window, start today.

The high-dose conversation (4 to 5 milligrams daily, not micrograms) is reserved for specific indications. Those include: a prior pregnancy affected by a neural tube defect, certain antiepileptic medications, type 1 or type 2 diabetes, malabsorption conditions, and in some guidelines a body mass index (BMI) over 30. Do not self-prescribe the high dose. It is a clinician decision based on your history.

The folic acid versus methylfolate (5-methyltetrahydrofolate, 5-MTHF) question deserves its own post because it has been thoroughly muddled by direct-to-consumer genetics. For most readers, ordinary folic acid is fine, and it is the form that was used in the trials that proved folate prevents neural tube defects. If you want the full breakdown of MTHFR variants, who actually needs the active form, and when higher dose matters more than the form, see folic acid vs methylfolate.

Vitamin D, if you are low

Vitamin D deficiency is genuinely common at higher latitudes, in people with darker skin tones, in people who work indoors, and in winter months. Most reproductive medicine reviews recommend aiming for a 25-hydroxyvitamin D (25(OH)D) level above 75 nanomoles per litre (30 nanograms per millilitre) before conception. Observational data link low 25(OH)D to lower IVF live-birth rates, longer time to pregnancy, and a higher rate of pregnancy complications such as gestational diabetes and pre-eclampsia.⁵ Randomised supplementation trials are less consistent on whether topping up vitamin D in a person who is already replete improves conception. Repletion in a person who is deficient is unambiguously sensible.

If you cannot test your level in time, a baseline of 1,000 to 2,000 international units (IU) of vitamin D3 daily, taken with a fat-containing meal, is reasonable for most adults. If you can test and you are deficient, a course of 4,000 IU per day for eight to twelve weeks, followed by a retest and a step-down to a maintenance dose, is a standard approach. The detail, including the threshold numbers, who to test, and what not to expect from vitamin D, is in vitamin D and fertility.

A basic prenatal multivitamin

Choose a prenatal that contains folate at 400 micrograms or more, iodine at around 150 micrograms, vitamin D at 10 to 25 micrograms (400 to 1,000 IU), and ideally choline at 100 milligrams or more. Iron is included in most prenatals at around 27 milligrams. If your ferritin is normal and the iron is making you nauseous or constipated, switching to a prenatal with less iron is a kinder approach. Add a targeted iron dose only if your ferritin is low.

Brand is largely irrelevant if the formulation is right. A competent prenatal exists at the eight-to-fifteen-pound monthly price point. Premium "fertility-branded" prenatals frequently cost three to five times more without a better folate dose, more choline, or more iodine. A prenatal that contains 10,000 IU or more of retinol vitamin A is the one to avoid; that dose is teratogenic, and most prenatals correctly use beta-carotene or cap retinol well below that threshold.

For the label-reading guide, including when to start, what to do if your current prenatal is missing one ingredient, and the gummies-versus-capsules question, see prenatal vitamins: when to start and which to pick.

Tier 2: situation-specific

Myo-inositol, if you have PCOS

Myo-inositol is one of the few over-the-counter supplements in fertility care that has multiple randomised controlled trials, meta-analyses, and guideline acknowledgement behind it. The mechanism is real: myo-inositol acts as a second messenger in insulin signalling, and PCOS involves insulin signalling dysfunction in most phenotypes, including lean PCOS. Supplementation can improve insulin sensitivity, lower circulating androgens, and restore ovulation in a meaningful fraction of users.

The standard dose is 2 grams of myo-inositol taken twice daily with food, paired with 50 milligrams of D-chiro inositol twice daily, in a 40:1 myo-to-DCI ratio. That ratio reflects the ratio found in healthy ovarian follicular fluid. The 2023 International Evidence-based Guideline for PCOS, the Teede guideline, acknowledges inositol as an experimental therapy with a favourable side-effect profile and notes that women may choose to use it, while not making a strong first-line recommendation.⁶ A 2017 meta-analysis by Unfer and colleagues found consistent improvements in ovulation rate, menstrual regularity, and metabolic markers across the trials.³

Inositol does not cure PCOS, does not replace lifestyle work, and does not replace letrozole or clomiphene if you are actively trying with anovulatory cycles. It is a baseline support that builds over eight to twelve weeks. For the dose, the ratio, how it fits with metformin and letrozole, and the D-chiro paradox that pure high-dose D-chiro can actually worsen oocyte quality, see myo-inositol and D-chiro inositol for PCOS fertility.

CoQ10, if you are over 35 or have diminished ovarian reserve

CoQ10 is essential to mitochondrial ATP production, and oocytes are uniquely mitochondria-dense. A single mature egg contains more than one hundred thousand mitochondria. Mitochondrial dysfunction is one of the better-supported mechanisms behind age-related decline in egg quality and aneuploidy. The Ben-Meir mouse study in Aging Cell in 2015 showed CoQ10 supplementation rescued oocyte mitochondrial function in aged mice and is the mechanistic anchor people cite.⁴ The human trials are smaller, more heterogeneous, and use a mix of clinical pregnancy and embryo quality as their outcome rather than live birth.

The honest framing is that CoQ10 is real, plausible, and modest. It is not a cure for age-related infertility, and I do not put it on the list for under-thirty patients with normal reserve. I do consider it for patients over thirty-five, for patients with documented diminished ovarian reserve, and for patients who are poor responders preparing for an IVF cycle. The dose range in the literature is 200 to 600 milligrams per day, taken with a fat-containing meal because CoQ10 is fat-soluble, started at least sixty to ninety days before the trying cycle or retrieval.

For the dose-form-timing detail, including when ubiquinol is worth the extra cost over ubiquinone and when CoQ10 simply is not the priority, see CoQ10 for egg quality.

Omega-3 DHA

Docosahexaenoic acid (DHA) at 200 to 300 milligrams per day supports fetal neurodevelopment. Some preconception data look at follicular fluid composition, but the strongest evidence is on pregnancy outcomes. Many modern prenatals already include DHA, so check the label before doubling up. If you eat oily fish twice a week, you are probably covered. If you do not, a separate algae-based or fish-oil DHA capsule is a reasonable addition.

Iodine, if your prenatal does not include it

Iodine is required for fetal brain development. UK-formulated prenatals often omit it, while US prenatals usually include 150 micrograms. The Avon Longitudinal Study of Parents and Children (ALSPAC) found that mild-to-moderate iodine deficiency in UK pregnant women was associated with lower verbal IQ in their children at age eight. If your prenatal does not contain iodine, add a separate 150 microgram potassium iodide tablet, or switch brand.

Tier 3: the conversation list

The supplements in this tier are not on the shopping list. They are on the list of things to raise with your clinician if your situation suggests them.

NAC has small RCTs in PCOS and unexplained infertility. It is not standard of care, and its place in routine preconception is not established. I do not start it without a reason.

Melatonin has emerging IVF data on oocyte quality. It is sometimes added to a stimulation protocol by the reproductive endocrinologist (RE), not self-prescribed. The 2023 European Society of Human Reproduction and Embryology (ESHRE) add-ons guidance places melatonin in a research-only or neutral category.

DHEA is the one in this tier I want to flag most strongly: it should not be a self-prescribed supplement. DHEA is an androgen precursor, has real side effects, and is used in selected cases of documented diminished ovarian reserve under RE supervision. If a wellness website is selling you DHEA without a lab workup, walk away.

L-arginine has been studied for endometrial perfusion and ovulation induction adjunct use with mixed results. It is reasonable to discuss in specific scenarios; it is not on the baseline list.

What to skip, and why we keep being told to take them

Royal jelly, maca, vitex (chasteberry), and "fertility teas." No reliable randomised trial evidence for time to pregnancy or live birth. Vitex in particular has hormonal effects, no standard dose, and no quality control across brands. The marketing exists because the supplement industry is lightly regulated and these compounds are inexpensive to source and easy to sell.

"Fertility detox" or "cleanse" protocols: Biologically incoherent in healthy adults with working kidneys and a working liver. There is no detoxification benefit to short-term restrictive eating or supplement combinations marketed as cleanses, and they sometimes displace genuinely useful interventions.

Eighty-pound "egg quality" blends with proprietary ratios: The proprietary label is the tell. If a product cannot tell you the exact dose of each ingredient because the formula is "proprietary," you cannot match it to any trial. Most of these blends contain the Tier 1 and Tier 2 ingredients above at sub-trial doses, packaged for a markup.

Anyone, clinician or influencer, promising a specific percentage improvement in live birth from a supplement: There is no supplement that improves live birth by a defined percentage in the general TTC population. The number is invented.

The reason we keep being told to take these is that the supplement market is approximately a fifty-billion-dollar industry, fertility-marketing is one of its highest-margin segments, and a stressed pre-conception reader is one of its most receptive audiences. None of that is your fault. It is just useful to name.

How to actually build your stack: a decision tree

This is the version I would write on a piece of paper for a patient in clinic.

1. Pick one good prenatal multivitamin: look for folate 400 micrograms, iodine 150 micrograms, vitamin D 10 to 25 micrograms, and choline 100 milligrams or more. Take it daily, anchored to a habit such as toothbrushing or morning coffee.
2. Add vitamin D 1,000 to 2,000 IU if you have not been tested or if you have known low levels. If you can test and you are deficient, take 4,000 IU for eight to twelve weeks and retest.
3. Only if you have PCOS: add myo-inositol 2 grams plus 50 milligrams D-chiro inositol, twice daily with food, in the 40:1 ratio.
4. Only if you are 35 or older, or have documented diminished ovarian reserve, or are preparing for IVF as a poor responder: add CoQ10 200 to 400 milligrams daily with a fatty meal, ideally starting sixty to ninety days before the trying cycle or retrieval.
5. Stop. That is the stack for most readers. Anything else is a conversation with your clinician, not a default addition.

If your stack ends at step three and costs you fifteen to thirty pounds a month, you are doing this correctly. If it has eleven bottles in it, something has been added on faith rather than evidence.

What about the partner's stack?

The female stack is only half the picture. Sperm production takes approximately seventy-four days from spermatogenesis to ejaculation, which means the window for the partner to do meaningful preparation overlaps almost exactly with the female preparation window. The partner's stack is shorter (a basic men's multivitamin, zinc, vitamin D if low, and CoQ10 in specific male-factor scenarios) and is covered in the male fertility supplement guide. If both of you are doing this seriously, do it together.

What to ask before your next appointment

These are the questions worth taking into the GP or the RE visit, written down. Most clinicians will appreciate a focused list more than a general "what should I take?"

• What is my 25(OH)D level, and do I need to dose-adjust my vitamin D?
• Given my history, is there any reason to switch from folic acid to methylfolate, or to step up to the 5 milligram folate dose?
• Does my current prenatal cover iodine, choline, and DHA at the recommended doses, or do I need a separate tablet for any of them?
• Are there interactions between any supplement I am considering and any medication I am currently taking?
• If I have PCOS or known low ovarian reserve, is myo-inositol or CoQ10 specifically reasonable in my case?

Common worries: what's normal, what's a red flag

A few side effects come up often and are not a reason to stop.

• Mild nausea on a prenatal: try taking it with food or at bedtime, or switch to a different formulation. Some people tolerate split-dose (half in the morning, half in the evening) better than a single large tablet.
• Bright yellow urine on B-complex vitamins: this is riboflavin (vitamin B2) being excreted. It is normal, not a sign of overdose.
• Constipation from iron: switch to a slow-release form, to ferrous bisglycinate (which is gentler), or to a prenatal with less iron paired with a separate small iron dose only if your ferritin needs it.
• Mild bloating or loose stools on starting inositol: common in the first week. Start at half dose, titrate up over three to five days, and the gut usually settles.

A few symptoms are reasons to stop and contact your clinician.

• New rash, swelling, or breathing difficulty after starting any supplement.
• Jaundice, persistent right-upper-quadrant pain, or dark urine that does not resolve.
• Severe headache with visual change while on any new supplement.
• Pregnancy: at a positive test, stop any supplement that is not part of your prenatal stack and check in with your clinician about what to continue and what to drop.

A note on cost honesty

A defensible preconception supplement stack costs roughly fifteen to forty pounds, or twenty to fifty dollars, per month. Most of that is the prenatal multivitamin and vitamin D. The myo-inositol and CoQ10 additions, when indicated, will push the upper end. If you are spending more, you are probably paying for marketing, packaging, or a "fertility blend" that duplicates ingredients you already have in your prenatal.

The same applies to your partner's stack: a basic men's multivitamin, zinc, and vitamin D add up to under ten pounds a month at the supermarket. Anything beyond that should be tied to a specific reason.

You do not have to take everything to be doing this well. Folate, a good prenatal, vitamin D if low, and one situation-specific addition is a complete set of preconception supplements for most readers. That is the honest version.

What's next

• If you have PCOS: read myo-inositol and D-chiro inositol for PCOS fertility and PCOS, insulin resistance, and fertility.
• If you are 35 or older or have low ovarian reserve: read CoQ10 for egg quality.
• If you are not sure whether your current prenatal is the right one: read prenatal vitamins: when to start and which to pick.
• If you have been told you have an MTHFR variant: read folic acid vs methylfolate.
• For your partner's parallel stack: read male fertility supplements.

Sources

1. MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet 1991;338(8760):131-137. Link
2. Showell MG, Mackenzie-Proctor R, Jordan V, Hodgson R, Farquhar C. Antioxidants for female subfertility. Cochrane Database of Systematic Reviews 2020;(8):CD007807. Link
3. Unfer V, Facchinetti F, Orrù B, Giordani B, Nestler J. Myo-inositol effects in women with PCOS: a meta-analysis of randomized controlled trials. Endocrine Connections 2017;6(8):647-658. Link
4. Ben-Meir A, Burstein E, Borrego-Alvarez A, et al. Coenzyme Q10 restores oocyte mitochondrial function and fertility during reproductive aging. Aging Cell 2015;14(5):887-895. Link
5. Pilz S, Zittermann A, Obeid R, et al. The role of vitamin D in fertility and during pregnancy and lactation: a review of clinical data. International Journal of Environmental Research and Public Health 2018;15(10):2241. Link
6. Teede HJ, Tay CT, Laven JJE, et al. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Fertility and Sterility 2023;120(4):767-793. Link
7. Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Use of multivitamins, intake of B vitamins, and risk of ovulatory infertility. Fertility and Sterility 2008;89(3):668-676. Link