The advice around eating in pregnancy has accumulated a mixture of evidence-based recommendations, well-intentioned but unsubstantiated rules, and cultural mythology. The result is that pregnant women are frequently told to avoid things that are fine and not always told clearly about the things that genuinely matter.
What matters most is a varied, nutrient-dense diet supported by a small number of specific supplements – particularly folic acid and vitamin D – with awareness of a limited number of genuine food safety risks. The vast majority of dietary decisions in pregnancy do not have the degree of consequence that the volume of advice implies.
Healthbooq (healthbooq.com) covers nutrition and health in pregnancy.
Calorie Needs in Pregnancy
The widely cited advice to "eat for two" significantly overstates calorie requirements. In the first and second trimesters, calorie requirements do not increase substantially. In the third trimester, an additional approximately 200kcal per day is recommended – equivalent to a small banana and a handful of nuts, not a second meal.
Weight gain recommendations in pregnancy depend on pre-pregnancy BMI. The Institute of Medicine guidelines (widely used in the UK as well as the US) recommend total weight gain of 11.5-16kg for women with a pre-pregnancy BMI in the healthy range (18.5-24.9); less for women with higher pre-pregnancy BMI. Excessive weight gain in pregnancy increases the risk of gestational diabetes, large-for-gestational-age infants, caesarean delivery, and postpartum weight retention.
Essential Supplements
Folic acid: folate is a B vitamin involved in neural tube formation, which occurs between days 21-28 of pregnancy – before most women know they are pregnant. Neural tube defects (spina bifida and anencephaly) are reduced by approximately 70% when adequate folate is taken around conception. The NHS recommends 400 micrograms (0.4mg) of folic acid daily from preconception until 12 weeks of pregnancy. Women at higher risk (previous pregnancy affected by neural tube defect, taking anticonvulsant medication, BMI above 30, coeliac disease, diabetes) should take 5mg daily (available on prescription).
Vitamin D: the UK receives insufficient sunlight for vitamin D synthesis through the skin for much of the year, and dietary sources are limited. NICE and the NHS recommend 10 micrograms (400 IU) of vitamin D daily throughout pregnancy and breastfeeding. Vitamin D deficiency is associated with reduced bone mineralisation, impaired immune function, and poorer neonatal outcomes. Women with darker skin tones or who cover their skin outside have higher deficiency risk.
Iodine: iodine is essential for thyroid hormone production, and thyroid hormone drives fetal brain and nervous system development, particularly in the first trimester. UK soils are iodine-poor, and iodine intake in the UK population has fallen as dairy consumption has declined. Pregnant women should consume iodine-rich foods (dairy, fish, eggs) or take a supplement. Seaweed-based iodine supplements are not recommended because iodine content is highly variable. The Scientific Advisory Committee on Nutrition (SACN) recommends 140 micrograms of iodine daily in pregnancy.
Iron
Iron requirements increase significantly in pregnancy to support expanding blood volume and fetal iron stores. Iron deficiency anaemia is the most common nutritional deficiency in pregnancy, affecting approximately 15-20% of pregnant women in the UK. Haemoglobin is checked at the first antenatal booking and at 28 weeks.
Good dietary iron sources include red meat (haem iron, best absorbed), fortified cereals, lentils, pulses, and dark green vegetables (non-haem iron, absorbed less efficiently). Eating non-haem iron sources with vitamin C improves absorption. Tea and coffee consumed with meals significantly reduce iron absorption and are best avoided around mealtimes when iron intake is important.
Omega-3 DHA
Docosahexaenoic acid (DHA) is an omega-3 fatty acid essential for fetal brain and retinal development. The main dietary source is oily fish (salmon, mackerel, sardines, trout). The NHS recommends up to 2 portions of oily fish per week in pregnancy (but not more, due to environmental contaminants including mercury and dioxins). Women who do not eat oily fish can take a DHA supplement; algae-based DHA supplements provide a vegetarian option.
Fish to avoid in pregnancy (due to high mercury content): shark, swordfish, and marlin. These should be avoided completely. Tuna intake should be limited to 2 fresh steaks or 4 cans per week.
What to Avoid
Vitamin A (as retinol): high doses of vitamin A are teratogenic. Liver and liver products (pate, liver sausage) contain very high concentrations of retinol and should be avoided in pregnancy. Retinol-containing supplements (such as standard multivitamins not formulated for pregnancy) should be replaced with pregnancy-specific formulations that use beta-carotene instead.
Raw and undercooked meat and eggs; unpasteurised dairy and cheese with a white rind (brie, camembert, soft blue cheeses): risk of listeria and toxoplasma. Foods made with raw eggs (certain mousses, mayonnaise) pose a salmonella risk.
Alcohol: there is no established safe level of alcohol in pregnancy. The NHS and NICE recommend avoiding alcohol completely.
Key Takeaways
Pregnancy nutrition does not require eating for two – calorie requirements increase only modestly, by around 200kcal per day in the third trimester. Specific micronutrients have well-established importance in pregnancy: folic acid reduces neural tube defects by 70% and should be taken as a 400 microgram supplement daily from preconception until 12 weeks (5mg for women with higher risk); vitamin D (10 micrograms daily) supports fetal bone development and immune function; iodine supports fetal brain development; iron requirements increase in the second and third trimesters; and omega-3 DHA supports fetal brain and eye development. Vitamin A supplementation above safe amounts must be avoided as excess is teratogenic. The NHS recommends folic acid and vitamin D supplements for all pregnant women.
