The dietary advice given to pregnant women is overrun with rules. Some are evidence-based and load-bearing — folic acid, vitamin D, alcohol — and absolutely worth following. Some (no caffeine, no sushi ever, no soft cheese of any description) are blunt-instrument versions of more nuanced guidance. Some (eat for two, no spicy food, no exercise, raspberry leaf tea, pineapple at 38 weeks) are pure folklore. The result is that women often follow rules that don't matter while missing the ones that do.
This piece focuses on what the actual evidence supports — the small set of nutrients where the data is genuinely strong, and the limited list of foods where the risk is real enough to act on. The other 95 per cent of your diet just needs to be varied and reasonably balanced.
The Healthbooq app covers pregnancy alongside the early years; recording supplements taken and any iron-related symptoms gives your midwife better information at booking and 28-week reviews than recall alone.
"Eating for Two" — What's Actually True
Energy requirements in pregnancy increase modestly, not enormously:
- First trimester: essentially no extra calories needed. The early embryo is small; energy demands are negligible.
- Second trimester: roughly 340 kcal extra per day (US Institute of Medicine). UK guidance is more conservative.
- Third trimester: roughly 200–450 kcal extra per day, depending on guideline. NHS uses ~200 kcal — about a banana and a handful of almonds, or a slice of toast with peanut butter.
The "eating for two" framing predates accurate measurement of pregnancy energy demands and was pushed back in the 1980s by the Royal College of Obstetricians and Gynaecologists, but folklore has been slow to catch up.
Total weight gain depends on starting BMI. The Institute of Medicine ranges (used in both US and UK practice):
| Pre-pregnancy BMI | Recommended total gain |
|—|—|
| <18.5 (underweight) | 12.5–18 kg (28–40 lb) |
| 18.5–24.9 (normal) | 11.5–16 kg (25–35 lb) |
| 25.0–29.9 (overweight) | 7–11.5 kg (15–25 lb) |
| ≥30.0 (obese) | 5–9 kg (11–20 lb) |
Excess weight gain raises the risk of gestational diabetes, large-for-gestational-age babies, instrumental and Caesarean delivery, and postpartum weight retention. Insufficient gain raises the risk of small-for-gestational-age babies and preterm delivery. Most women will fall within range without weighing themselves; midwives in the UK don't routinely weigh after booking, while US prenatal care typically tracks weight at every visit.
The Supplements That Actually Matter
There are exactly three supplements every pregnant woman in the UK is recommended to take, plus a couple more in specific circumstances. Don't waste money on a multivitamin marketed for pregnancy if it doesn't contain these three at adequate doses.
1. Folic Acid — 400 micrograms daily (or 5 mg if higher-risk)
This is the single most important supplement, and the timing matters enormously. The neural tube — the structure that becomes the brain and spinal cord — closes between days 21 and 28 after conception, which is before most women know they're pregnant. Folate adequacy at that exact window reduces neural tube defects (spina bifida, anencephaly, encephalocele) by roughly 70 per cent (MRC Vitamin Study, 1991, The Lancet — landmark trial).
Standard recommendation: 400 micrograms (0.4 mg) of folic acid daily, from preconception to 12 weeks of pregnancy. Available over the counter at any pharmacy.
Higher-dose recommendation: 5 mg daily (prescription-only at this strength) — for women who:
- Have previously had a pregnancy affected by a neural tube defect
- Have a personal or family history of NTD
- Take antiepileptic medications (sodium valproate, carbamazepine, phenobarbital, phenytoin)
- Take other folate-antagonist drugs (some chemotherapy, sulfasalazine, methotrexate)
- Have BMI ≥30
- Have diabetes (type 1 or type 2)
- Have coeliac disease, sickle cell disease, or thalassaemia
UK food has been voluntarily fortified with folic acid for decades; mandatory fortification of non-wholemeal flour is being implemented from 2024 onward, which will further reduce population NTD rates but does not replace supplementation.
If you started folic acid only after a positive test, take it as soon as you remember and continue to 12 weeks. The window for prevention is the first month, but partial protection persists.
2. Vitamin D — 10 micrograms (400 IU) daily
UK latitude provides essentially no skin synthesis of vitamin D between October and April. Dietary sources (oily fish, eggs, fortified margarine) are limited. The default population assumption is that adults — especially pregnant women — are vitamin D insufficient through winter unless supplementing.
NHS recommendation: 10 micrograms (400 IU) daily throughout pregnancy and breastfeeding. Free under the NHS Healthy Start scheme for women receiving qualifying benefits.
Higher risk for deficiency: women with darker skin tones (more melanin reduces UVB-driven synthesis), women who cover their skin outdoors, women with limited outdoor time, women who are obese (vitamin D sequesters in adipose tissue). For these groups some clinicians measure 25-OH vitamin D and treat deficiency more aggressively.
Maternal vitamin D status influences fetal bone mineralisation, immune development, and possibly long-term bone health into childhood (MAVIDOS trial, Lancet Diabetes & Endocrinology 2016). Severe maternal deficiency is associated with neonatal hypocalcaemia and rickets.
3. Iodine — 140 micrograms daily
Iodine requirements rise sharply in pregnancy because thyroid hormone (which depends on iodine) drives fetal brain development, particularly in the first trimester. UK soils are iodine-poor and the dietary mainstays of iodine here are dairy products, eggs, and white fish. The Scientific Advisory Committee on Nutrition (SACN) recommends 140 micrograms daily in pregnancy and breastfeeding.
Most women hit this through diet alone if they regularly eat dairy and fish. Vegan and dairy-avoiding women, and women whose diets are low in fish, are the high-risk group — a UK iodine deficiency study (Bath et al., Lancet 2013) found around 60 per cent of pregnant women in a Surrey cohort were iodine-deficient by WHO criteria.
If supplementing, a pregnancy multivitamin (Pregnacare, Sanatogen Pronatal, Boots Pregnancy & Breastfeeding) will typically provide 140–200 micrograms of iodine — within the safe range. Do not use seaweed-based iodine supplements: kelp content varies enormously (from negligible to dangerously high), and excessive iodine can cause maternal or fetal hypothyroidism.
Iron — Treated If Low, Not Routinely Supplemented
Iron requirements roughly double in the second and third trimesters to expand maternal blood volume and lay down fetal iron stores. Iron deficiency anaemia (haemoglobin <110 g/L in the first trimester, <105 g/L from 28 weeks under UK guidelines) affects 15–20 per cent of UK pregnancies and increases the risk of preterm birth, low birthweight, and postpartum haemorrhage.
UK practice is to check ferritin/Hb at booking and at 28 weeks, and treat with oral iron (ferrous sulfate, ferrous fumarate) only if low — typically 100–200 mg elemental iron daily. Routine iron supplementation in non-anaemic women isn't recommended because of side effects (constipation, nausea, GI upset) and because excess iron in pregnancy is linked to its own complications.
If you have iron-deficiency anaemia:
- Take iron with vitamin C (orange juice, kiwi, tomato) to enhance absorption
- Take it on an empty stomach if tolerated; with food if not
- Avoid tea, coffee, and milk within 1–2 hours of the dose — tannins and calcium reduce absorption
- Alternate-day dosing has emerging evidence (Stoffel et al., Lancet Haematology 2017) that absorption is better than daily because of hepcidin response
DHA (Omega-3) — From Fish or Algae Supplement
Docosahexaenoic acid is required for fetal neural and retinal development, particularly in the third trimester. The richest dietary sources are oily fish: salmon, mackerel, sardines, trout, herring, kippers, fresh tuna.
NHS recommendation: up to two portions of oily fish per week in pregnancy (one portion = around 140 g cooked). Don't exceed two portions because of accumulated environmental contaminants (mercury, dioxins, PCBs).
If you don't eat fish, an algae-based DHA supplement (Pregnacare DHA, Vegan Pregnacare, Viridian Pregnancy Omega 3 Vegan) provides 200–500 mg DHA per day and is a clean alternative — algae are where fish get DHA from in the food chain. The Cochrane review (2018) of omega-3 supplementation showed a reduction in preterm birth (<37 weeks) of around 11 per cent and in early preterm birth (<34 weeks) of around 42 per cent in supplemented women.
Foods to Actually Avoid (Short List)
Most pregnancy "avoid" lists are too long. Here's the short, evidence-based version:
Always avoid:
- Liver and liver products (pâté, liver sausage, foie gras). Vitamin A as retinol is teratogenic at high doses; liver delivers a single-meal retinol load that can exceed safe limits. Beta-carotene from carrots and pumpkins is not the same molecule and is fine.
- Standard multivitamins not formulated for pregnancy if they contain retinol. Pregnancy formulations use beta-carotene.
- Shark, swordfish, marlin. High methylmercury accumulation. Tuna intake limited to 2 fresh steaks or 4 medium cans (140 g) per week.
- Alcohol. No safe level has been established for any trimester. UK CMO and NICE guidance: avoid completely.
Listeria-prevention list (the UK NHS and US CDC lists are similar):
- Unpasteurised milk and unpasteurised soft cheeses
- Mould-ripened soft cheeses (brie, camembert, chèvre with rind) and soft blue cheeses (Roquefort, Danish blue, gorgonzola) — unless cooked through and bubbling
- Pâtés (animal or vegetable; the listeria risk is in the manufacture, not the meat itself)
- Cold cured meats — UK 2017 advice now permits these if heated through; raw cold ham/salami carries a small toxoplasma risk but the evidence here is less robust than for listeria
- Smoked or cold-cured fish only if shop-bought, refrigerated correctly, and within use-by date
Salmonella-prevention:
- Raw or partially cooked eggs unless British Lion-marked (these are now considered safe to eat raw in pregnancy under UK Food Standards Agency 2017 guidance — homemade mayonnaise, soft-boiled eggs, runny yolks)
- Imported (non-Lion) eggs should be cooked through
Toxoplasmosis-prevention:
- Cured meats not heated through (parma ham, salami)
- Raw or undercooked meat
- Unwashed soil-grown vegetables
- Wear gloves when gardening; wash hands after handling cat litter (or get someone else to do it)
Things that are fine but commonly avoided unnecessarily:
- Most cheese — hard cheeses (cheddar, parmesan, gouda) are fine; pasteurised soft cheeses without rinds (mozzarella, ricotta, cottage cheese, feta, paneer, halloumi, cream cheese) are fine
- Sushi made with previously-frozen fish in reputable restaurants is generally fine in the UK (FSA 2017); the older blanket ban relates to freshly-caught fish and parasites
- Coffee — up to 200 mg of caffeine daily is considered safe (one filter coffee or two instant)
- Spicy food, peanut, garlic, exercise, sex — all unaffected by pregnancy under normal circumstances
The Big Picture
The evidence-supported pregnancy diet is not exotic. It looks like:
- A varied diet built around vegetables, fruit, whole grains, dairy or fortified plant milks, legumes, eggs, lean meat or fish
- A small daily folic acid + vitamin D + iodine supplement (or a pregnancy multivitamin that delivers these), preferably starting before conception
- Two portions of oily fish a week, or an algae DHA supplement
- An iron supplement only if you become anaemic
- Avoidance of the short list above
Stress about specific foods less than the women's-magazine industry would suggest. Stress about supplements more than your great-aunt does. Most of the dietary work that affects your baby is being done by the unremarkable contents of your normal weekly shop.
Key Takeaways
Pregnancy is not a time of doubled calorie needs (third trimester adds about 200 kcal — a banana and a small handful of nuts). The bits that genuinely matter are a short list of micronutrients with strong evidence: 400 micrograms of folic acid daily from preconception through 12 weeks (5 mg if higher-risk), 10 micrograms of vitamin D throughout pregnancy and breastfeeding, 140 micrograms of iodine, adequate iron, and DHA from oily fish twice a week or an algae supplement if you don't eat fish. Foods to actually avoid: liver and pâté (retinol toxicity), shark/swordfish/marlin (mercury), unpasteurised dairy and certain soft cheeses (listeria), and alcohol entirely. Most other 'pregnancy food rules' are folklore.
