Women pre-pregnancy or in the earliest stages of pregnancy often visit the GP for lifestyle advice, and this is a good opportunity to give a clear message about good nutrition.
The risk of spina bifida may be reduced by folic acid supplementation
Pre-pregnancy and the first trimester is probably the most crucial time in terms of nutrition, but ironically is often a stage that is completely missed, because a woman may not even know that she is pregnant.
Women stopping contraception to try for a baby should be advised to aim for a healthy balanced diet (see box) and try to maintain a healthy weight before conception. A folic acid supplement - 400 microgram - is recommended from preconception until week 12 of pregnancy.
Women at increased risk of having a baby with a neural tube defect (NTD) should be prescribed a 5mg folic acid supplement.
Women at higher than average risk are those who have previously given birth to a baby with an NTD; are taking an antiepileptic medication; have an NTD (or their partner has an NTD); have coeliac disease or diabetes.
NHS Healthy Start vitamin supplements contain vitamins D and C and folic acid and are specially formulated for women trying to conceive, pregnant and breastfeeding women. These are free for many women in receipt of benefits, and some PCTs have a policy to provide them free to all pregnant women.
Studies have established good nutrition as vitally important in pregnancy1, as malnutrition during critical periods of fetal growth can permanently impair physiology and metabolism.
There is no increase in calcium requirements during pregnancy, but adolescent girls who become pregnant should ensure that adequate amounts of calcium-rich foods are included to meet the demands of pregnancy in addition to their own physiological needs.
During pregnancy, iron requirements increase to meet the demands of increased red blood cells, the growing fetus and placenta, but there is no recommendation to increase iron intake, since the extra iron is acquired through the cessation of menstruation and increased intestinal absorption of iron.
However, many women have low iron stores and are at increased risk of anaemia.2 Dietary sources of iron such as red meat, pulses, dark green leafy vegetables and fortified cereals should be encouraged.
Vitamins C and D
An increase of 10mg of vitamin C is needed during the last trimester. Foods rich in vitamin C - such as orange juice - can help to increase absorption of iron.
During the whole of pregnancy, 10 microgram vitamin D is recommended. Women at risk of vitamin D deficiency - those with darker skin or those who cover their skin - are advised to take a vitamin D supplement.
Advice on foods to avoid during pregnancy is listed on the Food Standards Agency website.3
Advice is based on general hygiene when preparing foods, especially raw meat, but also includes avoiding bacteria that are potentially harmful during pregnancy (see box below).
An additional 200kcal per day is required during the last trimester of pregnancy only, but a woman should be advised to eat a healthy diet according to her appetite.
It is rare for midwives to monitor weight gain during pregnancy. According to the WHO,4 for women with a normal pre-pregnancy weight, an average weight gain of 10-14kg is associated with the lowest risk of complications.
Fish and shellfish
Some types of fish, including marlin, shark and swordfish can have a high mercury content, which can cause neurological damage in the fetus.
Tuna can be eaten safely at low levels: no more than two fresh tuna steaks or four medium cans of tuna per week. No more than two portions per week of oily fish should be consumed.
Raw shellfish should also be avoided due to the risk of potential bacterial contamination.
Liver and vitamin A
High intakes of vitamin A during pregnancy have been found to be teratogenic. Animal studies have shown that high doses of vitamin A-related compounds have been associated with congenital defects and abnormal growth, particularly if high doses are taken in the first trimester.5
Being high in vitamin A, all liver products (including pates) should be avoided during pregnancy. Vitamin supplements not specially formulated for pregnant women can also contain too much vitamin A.
Studies suggest that caffeine should be limited to 300mg per day to reduce risk of miscarriage or low birth weight. Foods that contain caffeine include coffee (100mg per mug), tea (50mg per cup), cola (40mg per can), plain chocolate (50mg per 50g bar).
The DoH and the Royal College of Obstetricians and Gynaecologists recommend that alcohol should be avoided completely during pregnancy as there is no recognised safe limit, but women who do drink should have no more than one or two units, not more than once or twice per week.6,7
- Dr Phillips is a registered dietitian based in Devon and public relations officer for the British Dietetic Association.
A healthy diet in pregnancy applies also to the general population
- At least five portions of fruit and vegetables a day.
- Base meals on starchy carbohydrates.
- At least two foods rich in protein every day - meat, fish, eggs and pulses.
- Dairy foods for calcium (or calcium-fortified non-dairy foods, eg soya milk).
- Plenty of fibre from whole-grain cereals, pulses, fruit and vegetables - this will help prevent constipation.
|Foods to avoid in pregnancy2|
|Pathogen||Foods to avoid||Consequence of infection||Notes|
Pate (including vegetable pate), mould-ripened and soft cheeses (brie, Camembert, blue-veined cheeses), unpasteurised dairy products
|Can cause miscarriage and still birth Notes: Destroyed by heat - prepared meals should be reheated thoroughly.||Destroyed by heat - prepared meals should be reheated thoroughly.|
|Salmonella||Raw eggs or foods containing these (such as fresh mayonnaise or mousse)||Can cause miscarriage or premature labour in severe cases||Cook eggs, meat and poultry thoroughly|
|Toxoplasmosis||Raw and undercooked meat; unpasteurised dairy products (especially goats' milk)||Rare, but can lead to severe congenital toxoplasmosis||Avoid contact with soil and cat litter trays|
|Campylobacter||Raw or undercooked poultry, unpasteurised dairy products||May cause premature birth, spontaneous abortion or stillbirth||Domestic pets and soil can also be a source of infection|
1. Barker D. Fetal and infant origins of adult disease. London: BMJ Publishing Group, 1992.
2. British Nutrition Foundation. Nutrition in Pregnancy. Oxford: Blackwell Science, 2006.
4. WHO. Maternal Anthropometry and pregnancy outcomes. A WHO Collaborative Study. WHO Bulletin 1995; 73(Suppl): 1-98.
5. Hathcock JN, Hattan DG, Jenkins MY et al. Evaluation of vitamin A toxicity. Am J Clin Nutr 1990; 53: 183-202.
7. Royal College of Obstetricians and Gynaecologists. Alcohol and pregnancy: Information for you. London: RCOG, 2006. www.rcog.org.uk/index.asp?PageID=1816