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Eating for two? Nutrition advice during pregnancy

Hannah Theobald
PhD BSc RPHNutr
Public Health Nutritionist
The Sugar Bureau
London

Nurses and other healthcare professionals are one of the most trusted sources of dietary and nutritional information for women during pregnancy. For this reason it is important that they are up-to-date with current findings and nutritional advice.

What is a healthy balanced diet?
A healthy and balanced diet includes a wide variety of foods to ensure an adequate intake of nutrients. A diet rich in starchy carbohydrates (bread, pasta, rice and breakfast cereals, for example) and fruits and vegetables forms the basis of a healthy and balanced diet; these two important food groups should each form a third of food intake. A balanced diet includes moderate amounts of meat, fish, eggs and other protein-rich foods, milk and dairy products, and moderate amounts of fat.
Following a healthy diet is important to ensure an adequate nutritional intake both before and during pregnancy to support the growth and development of the fetus. It is advised, therefore, that pregnant women eat plenty of fruits, vegetables, starchy foods and fibre (to help prevent constipation during pregnancy), foods rich in protein, and milk and dairy foods. While physiological adaptations will cover much of the increased requirements for energy, protein and certain micronutrients during pregnancy, particular emphasis should be placed on encouraging adequate intakes of folate, iron, calcium and vitamin D. It is also important that pregnant women, or those who wish to become pregnant, are of a healthy body weight (BMI 18.5-25). As a considerable number of pregnancies are unplanned, many pregnant women may be far from the ideal nutrient status. They should therefore attempt to correct this.

Essential nutrients during pregnancy

Folate/folic acid
Folate (or folic acid, the synthetic form of folate) is required for the normal structure of neural tubes. It is found naturally in fruits and vegetables such as oranges and asparagus, beans and broccoli, as well as brown rice. Folate is also added to a number of breakfast cereals in the form of folic acid. Folic acid supplementation is associated with a reduced risk of neural tube defects (NTDs, eg, spina bifida and stillbirth). It is recommended that all women of childbearing age take a dietary supplement providing 400mg of folic acid/day up until 12 weeks of pregnancy in addition to the 200mg a day dietary reference value for folate from food for this group of women.(1) Women who have previously had an NTD-affected pregnancy are advised to take a supplement providing 5mg folic acid a day. It is reported that 55% of women planning to become pregnant take a folic acid supplement or make attempts to increase dietary folate intake. Women in the older age groups are more likely to make a conscious effort to increase folate intake. Women living in socially  deprived areas are less likely to increase folate intake prepregnancy (43%), compared with women in more affluent areas (70%).(2)

Iron
Iron, required for the formation of healthy red blood cells, oxygen transport and the immune system, is lacking in many women's diets (pregnant and nonpregnant). As a result, many women require iron supplements during pregnancy. Dietary requirements for iron do not increase during pregnancy as menstruation ceases and iron absorption increases, but foods rich in iron should be encouraged. Iron is found in foods of both plant and animal origin (eg, red meat and eggs); however, iron from animal sources (haem iron) is most readily absorbed. Nonhaem iron, found in plant foods, is less readily available to the body due to the presence in plant foods of compounds that inhibit absorption.  The absorption of nonhaem iron, found in fortified breakfast cereals, bread (both fortified with iron), pulses and dried fruits can be increased by the consumption of vitamin C (eg, citrus fruit juice).

Calcium
An adequate intake of calcium is required for fetal bone development. The skeleton of full-term infants contains 20-30g of calcium. Most of this calcium is accrued during the last trimester of pregnancy, when maternal absorption rates increase from 20-30% up to 60% as a result of physiological adaptations during pregnancy. As a result of the upregulation in calcium absorption, dietary requirements for calcium do not increase. However, it is important that pregnant women consume enough calcium, and that calcium-rich foods are encouraged. Most calcium in the UK diet is acquired from milk and dairy products, foods from which calcium is readily absorbed. Other sources of calcium include: brown and white (but not wholemeal) breads, canned fish (except tuna) where the bones are eaten, nuts and pulses, and calcium-fortified foods, such as certain breakfast cereals.

Vitamin D
Vitamin D plays a role in cell division and is needed for calcium absorption as well as normal bone formation and therefore fetal growth. While vitamin D can be acquired from the diet (oily fish, eggs, margarine and vitamin D-fortified breakfast cereals) the majority of vitamin D in the body is synthesised following exposure of the skin to sunlight. However, some groups of the population have limited skin exposure to sunlight (eg, Asian women and women who rarely go outdoors or always cover their skin when outside) and may have an inadequate vitamin D status. This is associated with low bone density and may have implications for rickets in childhood and osteoporosis in later life. For this reason it is recommended that all pregnant women take a vitamin D supplement providing 10μg a day.

Energy
The estimated energy requirement for a woman of childbearing age is 8.1MJ a day (1,940kcal). The requirement does not increase during the first two trimesters of pregnancy, but during the last trimester energy should be increased by 0.8MJ a day (200kcal) to correspond with the rapid growth of the fetus.(3)

Weight gain and weight loss diets
A weight gain of 12.5kg is considered to be optimal during pregnancy. Such weight gain is associated with the lowest risk of having a low-birthweight baby and having complications during pregnancy and labour. This degree of weight gain should not be discouraged as this is a natural process during pregnancy; low weight gain is associated with a low-birthweight infant and premature birth, especially in under- or normal-weight women prepregnancy. However, excess weight gain should not be encouraged, as this is associated with gestational diabetes and postpartum overweight or obesity in the mother. Weight loss and dieting should not be encouraged during pregnancy, as restricting food intake may lead to inadequate nutrient intake, which could compromise fetal growth and development.(4)

Foods to avoid or eat sparingly during pregnancy
Food safety is essential during pregnancy as food-borne pathogens can cause illness or damage the developing fetus. For this reason it is advised that pregnant women avoid foods that may harbour pathogenic bacteria. Below is a list of some other foods that should be avoided during pregnancy because they contain substances or high amounts of nutrients that may harm the developing fetus.

Shark, swordfish and marlin
It is important that pregnant women consume one to two portions of oily fish (such as trout, sardines and sprat) per week to provide the developing fetus with long-chain omega-3 fatty acids. However, pregnant women should avoid eating shark, swordfish and marlin. These large predatory fish can contain high concentrations of environmental contaminants in the form of methylmercury that can damage the developing fetus's nervous system. It is recommended that pregnant women limit their consumption of tuna to no more than two fresh tuna steaks per week (170g raw weight) or four medium cans of tuna (drained weight 140g).

Raw and partially cooked eggs, meat and shellfish
The Food Standards Agency recommends that pregnant women should avoid eating raw and partly cooked eggs, raw or undercooked meats, and shellfish to reduce the risk of bacterial food poisoning such as salmonella, which may cause harm to the developing fetus. It is recommended that pregnant women eat eggs cooked so that the yolk and the white are both solid and eat meat that is well cooked, particularly burgers, sausages and other products made from minced meat. It is also important that they avoid mayonnaise, ice cream and salad dressing that may have been made with unpasteurised raw eggs. Most shop-bought versions will contain pasteurised eggs; if not, they will be labelled otherwise.

Pâté
All pâtés, including vegetarian pâtés, should be avoided during pregnancy as they may contain Listeria monocytogenes. Listeriosis can be transmitted to the developing fetus, causing miscarriage, premature delivery, stillbirth or other serious complications.

Liver, liver pâté and liver sausages and supplements containing vitamin A
These foods contain high amounts of vitamin A in the form of retinol. High intake of vitamin A can be teratogenic. For the same reason, women should avoid dietary supplements containing retinol, including fish liver oils.

Certain cheese
During pregnancy it is advised that women avoid cheese with rinds (ie soft, mould-ripened cheese such as Brie, Camembert and chèvre), along with blue cheeses, as these could contain L monocytogenes.

Alcohol
Some women choose to abstain from alcohol while others will continue to enjoy alcohol during pregnancy. For women who choose to drink alcohol, it is recommended that they do not consume more than one to two units of alcohol on more than one or two days each week and avoid binge drinking. A unit of alcohol is classed as 25ml of spirits, or a half pint of ordinary strength lager, while a 175ml glass of wine counts as two units. Drinking more than three alcoholic drinks a week during the first trimester of pregnancy is associated with an increased risk of miscarriage; heavy drinking is associated with low birthweight and fetal alcohol syndrome, characterised by growth retardation and congenital and facial abnormalities.(5) High intake of alcohol can interfere with the absorption of folate.

Caffeine
Consumption of chocolate and caffeine-containing drinks should be limited during pregnancy to no more than 300mg a day, as high intakes of caffeine are associated with low birthweight and miscarriage. This is equal to three cups of tea plus a can of cola, a cup of instant coffee and a 50g bar of chocolate. Table 1 shows the amount of caffeine in different beverages and chocolate.

[[NIP29_table1_72]]

Peanuts
The Food Standards Agency currently recommends that if there is a close family history of food or animal allergy, asthma, eczema or hayfever, the pregnant woman should avoid food containing peanuts, to reduce the risk of the baby developing a potentially fatal peanut allergy.(6)

Conclusion
Pregnancy is a time in life when women are particularly receptive to receiving sound nutritional advice from trained healthcare professionals. Pregnant women should be advised to remain as physically active as possible to promote health and wellbeing, maintain fitness and prevent excess weight gain. Many women continue after the birth to keep up the changes they make to their lifestyle during pregnancy, greatly benefiting themselves and the rest of the family too. It is therefore important to encourage women to follow a healthy balanced diet during pregnancy, taking heed of the additional dietary advice.

References

  1. Department of Health. Dietary reference values for food energy and nutrients for the UK. London: HMSO; 1991.
  2. Blake M, et al. Health survey for England 2002: maternal and infant health. London: TSO; 2003.
  3. Department of Health. Folic acid and the prevention of neural tube defects. London: HMSO; 1992.
  4. Anderson AS. Symposium on "nutritional adaptation to pregnancy and lactation". Pregnancy as a time for dietary change? Proc Nutr Soc 2001;60:497-504.
  5. RCOG. Alcohol consumption in pregnancy. London:RCOG; 1999.
  6. Food Standards Agency. Available from: http://www.eatwell.gov.uk

Resource
Williamson CS. Nutrition in pregnancy.
Nutr Bull 2006;31:28-59.