Nutrition Guideleines for pregnancy
Pregnancy is a time when appetite is altered and nutritional needs change. What the expectant mother eats or drinks can affect her baby’s health and her own comfort. In pregnancy women develop a new interest in the consequences for health of what they eat.
Pregnancies in women who are overweight, have anorexia nervosa, or whose growth is not completed are more difficult, and these women need extra nutritional care.
A good intake of folate is important in preventing neural tube defects and some other malformations in the fetus of a minority of women. The stage when this vitamin is most needed is the first 28 days after conception so supplementation or high folate diet has to be periconceptional. Likewise, it is the early weeks when excess alcohol intake may lead to malformations.
During pregnancy extra nutrients are required, especially from 20 weeks, for the growing fetus and for the placenta. Tissue is also laid down in the uterus and breasts, blood volume is increased, and, in healthy women with adequate food, adipose tissue increases by around 2.7 kg. This fat is deposited more on the hips and thighs.
Alcohol in pregnancy
• Heavy drinkers have a greatly increased risk of inducing the fetal alcohol syndrome— characteristic underdevelopment of the mid face, small size, and mental retardation.
• Women who intend to become pregnant should not sit drinking whatever the occasion: they could be two or three weeks pregnant.
• Once pregnancy is established the rule should be no more than one alcoholic drink a day to be sure of preventing minor effects, chiefly growth retardation.
Nutrition for pregnancy
The extra energy need for a pregnancy can be calculated as about 250 MJ (60 000 kcal). This includes energy stored in fetal fat and protein, and in maternal reproductive tissues and adipose tissue. It takes account of the mother’s increased basal metabolic rate and the energy needed to move a heavier body.
This corresponds to 1 MJ (240 kcal) a day (excluding the first month, for 250 days), daily intake of energy during pregnancy (10 MJ, 2400 kcal) above the non-pregnant amount (9 MJ or 2150 kcal). The extra energy need is probably balanced by decreased exercise and increased efficiency of metabolism. Pregnant women seem to reduce their exercise if they can. Postprandial cholecystokinin concentrations increase, which enhances nutrient absorption and the anabolic actions of insulin.8 So it is not true that a pregnant woman has to eat calories for two, but a few nutrients should be substantially increased.
The amounts of different nutrients which the mother has to put into her fetus by the time of delivery have been worked out by chemical analysis of stillbirths. These can be estimated more accurately for stable inorganic elements than for the vitamins. From these figures for nutrients accumulated and from information on whether there is any change in their absorption and turnover, the extra requirements for pregnancy can be estimated.
The metabolism of protein is more efficient and so is the absorption of iron in pregnancy. For most nutrients like protein the small extra amounts required are covered adequately by a normal diet. But intakes are more critical for the other five nutrients in the table showing recommended daily intakes.
||Addition for pregnancy
| Protein (g)
| Folate (microgram total folate)
| Calcium (mg)
| Iron (mg)
| Zinc (mg)
| Iodine (microgram)
Folate is the only vitamin, and iron the only nutrient element whose requirements double in pregnancy. Extra folate is needed for the first month and again for the last trimester. Serum and red cell folate concentrations decline in pregnancy and, if looked for, some degree of megaloblastic change can be found in substantial minorities of women in late pregnancy.
Such changes have been reported in 6-25% of women not taking supplements in Britain. The word folate comes from the Latin folia (leaf) because it was first found in spinach, but food sources are not the same as for vitamin C. Whole grain cereals, nuts, and legumes are good sources of folate. The vitamin is largely destroyed by prolonged boiling.
The iron content of the fetus (about 300 mg), placenta (50 mg), and average postpartum blood loss (200 mg) add up to some 550 mg. The red cell mass also increases after 12 weeks by an amount which corresponds to about another 500 mg of iron, but this is a temporary internal borrowing from stores and causes no extra demand provided the stores are sufficient.
Against these extra needs there is the saving from no menstruation (some 200 mg) and improved intestinal absorption. Maternal haemoglobin concentration declines by about 10% because of physiological haemodilution; and serum iron concentration, transferrin saturation, and ferritin concentration all go down. These changes can be partly—but only partly—prevented by iron supplementation.
With calcium, absorption becomes more efficient. Without any change of vitamin D intake or exposure to the sun, plasma concentrations of calcitriol (the active form of the vitamin converted in the kidney) are increased. Some of this extra conversion takes place in the placenta. The easiest way of obtaining the extra calcium needed for pregnancy and lactation is from milk; 0.5 litre supplies about 600 mg calcium. The increased need for iodine may be taken for granted, but in areas where goitre is endemic there is a risk of cretinism. In such areas expectant mothers should be given an injection of iodised oil, preferably before conception.
Iron in pregnancy
There is no universal policy. Some doctors are more interventionist than others. Iron tablets can cause indigestion or constipation. The following is generally agreed.
Women should be advised to eat meat regularly (unless vegetarian). This is the best absorbed source of iron in the diet.
A woman with a history of anaemia, menorrhagia, poor diet, or repeated pregnancies should be given iron supplements or an iron-folate preparation.
Haemoglobin should be checked and iron given if it is below 110 g/l (with a low mean cell volume).
For prophylactic purposes one iron tablet a day is adequate.
With the smaller dose of iron, side effects are fewer and compliance should be better.
The amount of weight gained from before conception to shortly before delivery ranges considerably in normal women— from about 6 to 24 kg. A good average to try to achieve is 12 kg (26 lb). This might be made up of about 115 g (1/4 lb)/week for the first 10 weeks and 300 g (2/3 lb)/week for the remaining 30 weeks. A mother’s height, her weight for height at the start of pregnancy, and her weight gain can all influence the size of the fetus. Birth weights are lower in babies of mothers who choose (against medical advice) to continue to smoke during pregnancy. In affluent countries the body fat gained during pregnancy can persist after childbirth.
Pregnancy is one of the factors that can predispose to obesity.
Obesity in pregnancy increases the chances of a heavier and fatter baby and also of hypertension and gestational diabetes. Since 3 to 4 kg of the usual 12 kg weight gain is fat, overweight women should try to put on only 7 to 8 kg overall during their pregnancy.
Hypertension and “toxaemia”
In pregnancy-induced hypertension (toxaemia) no excess of sodium is retained. It is proportional to the fluid retained. No evidence exists that either a high or a low salt diet predisposes to pregnancy-induced hypertension or that any other dietary component—energy, protein, or any micronutrient—is directly responsible, except perhaps calcium deficiency.
Diet and discomforts of pregnancy
Nausea and vomiting of pregnancy (NVP) is not confined to the mornings (so “morning sickness” is a misleading name). It is probably due to rising levels of pregnancy-associated hormones and often accompanied by increased olfactory sensitivity and aversion to strongly flavoured food and drink. In developed countries normal NVP appears to be beneficial, not detrimental to the fetus. There has been no controlled trial of simple management. One opinion is that it is related to a low blood glucose concentration and that a dry biscuit or similar light snack before getting up may help. It now seems possible that the increased cholecystokinin concentration could explain the symptoms. Unlike other conditions that cause nausea, women tend to put on weight during the phase of morning sickness. Severe, persistent NVP, hyperemesis gravidarum is uncommon. When it occurs, note that thiamin is the most critical micronutrient.
Constipation and its complication haemorrhoids are very common in pregnancy. All pregnant women should be advised to eat more wholemeal bread, bran, or bran cereals to loosen and increase the bulk of their faeces.
Heartburn should improve if the woman eats smaller meals and avoids foods which she finds indigestible. The common meal pattern of tiny breakfast, small lunch, and large dinner becomes unsuitable in late pregnancy. It is a good plan for her to have four, five, or even six small meals throughout the day. This also helps NVP.
Cravings and aversions—at some stage in pregnancy most women experience a distortion of their usual range of likes and dislikes of foods. Women may develop a nine-month aversion to foods they usually like—for example, fried foods, coffee, tea. Contrariwise and at the same time they may experience a craving for certain foods. These are often sweet foods, such as fruits and chocolate ice cream, and sometimes salty, but some remarkable non-foods—coal, soap, soil—have been recorded.
Vegetarians who are pregnant may need extra dietary advice. There are several types of vegetarian. Those most at risk are vegans. It is essential for them to take a supplement of vitamin B-12 for normal cerebral development of the fetus. Other lacto-ovo vegetarians, especially if they are prosperous and belong to a traditional vegetarian group, usually manage well enough but may want or need advice to optimise their protein and iron intakes. Legumes and nuts are an important part of a balanced vegetarian diet.
Food safety in pregnancy
Avoid unpasteurised milk, soft cheeses and raw eggs—danger of listeria and salmonella infection is more serious in pregnancy.
Pre-cooked foods (for example, pies) should be thoroughly re-heated before eating.
Avoid extra vitamin A, in the form of supplements or multivitamins containing vitamin A, or liver more than occasionally in early pregnancy. Retinoic acid is involved in normal morphogenesis and excess can be teratogenic.