Nutrition in pregnancy and medication introductory comments:
Prenatal care is vitally important for the health of the unborn baby. A pregnant woman should be sure to eat a balanced, nutritious diet of frequent, small meals. Women should begin taking 400 mcg of folic acid several months before becoming pregnant, as folic acid has been shown to reduce the risk of spinal cord defects, such as spina bifida.
No medication (not even a nonprescription drug) should be taken except under medical supervision, since it could pass from the mother through the placenta to the developing baby. Some drugs, called teratogens, have been proven harmful to a fetus, but no drug should be considered completely safe (especially during early pregnancy). Drugs taken during the first three months of a pregnancy may interfere with the normal formation of the baby’s organs, leading to birth defects.
Drugs taken later on in pregnancy may slow the baby’s growth rate, or they may damage specific fetal tissue (such as the developing teeth), or cause preterm birth. Herbal supplements and other ‘‘natural’’ remedies can also be extremely harmful to an unborn baby and should not be taken during pregnancy without close supervision by a physician.
To have the best chance of having a healthy baby, a pregnant woman should avoid:
- street drugs
- large amounts of caffeine
- artificial sweeteners
Women should begin following a healthy diet even before they become pregnant. This means cutting back on high-calorie, high-fat, high-sugar snacks, and increasing the amount of fruits, vegetables, and whole grains in her diet. Once she becomes pregnant, she should make sure to eat at least six to 11 servings of breads and other whole grains, three to five servings of vegetables, two to four servings of fruits, four to six servings of milk and milk products, three to four servings of meat and protein foods, and to drink six to eight glasses of water each day. She should limit caffeine to no more than one soft drink or cup of coffee per day.
Advice from NHS choices in UK:
Eating a healthy, varied diet in pregnancy will help you to get most of the vitamins and minerals you need. There are some vitamins and minerals that are especially important. It is best to get vitamins and minerals from the food you eat, but when you are pregnant you will need to take some supplements as well to make sure you get everything you need.
It's recommended that you take:
- 10 micrograms of vitamin D each day throughout your pregnancy and if you breastfeed
- 400 micrograms of folic acid each day – you should take this from before you are pregnant until you are 12 weeks pregnant
Do not take vitamin A supplements, or any supplements containing vitamin A (retinol), as too much could harm your baby.
You can get supplements from pharmacies and supermarkets, or your GP may be able to prescribe them for you. If you want to get your folic acid or vitamin D from a multivitamin tablet, make sure that the tablet does not contain vitamin A (or retinol).
Folic acid is important for pregnancy as it can help prevent birth defects known as neural tube defects, such as spina bifida. You should take a 400 microgram folic acid tablet every day while you are trying to get pregnant and until you are 12 weeks pregnant. If you didn't take folic acid before you conceived, you should start as soon as you find out that you are pregnant.
You should also eat foods that contain folate (the natural form of folic acid), such as green leafy vegetables and brown rice. Some breakfast cereals, breads and margarines have folic acid added to them. Find out more about healthy eating in pregnancy.
Some women have an increased risk of having a pregnancy affected by a neural tube defect, and are advised to take a higher dose of 5 milligrams (5mg) of folic acid each day until they are 12 weeks pregnant. Women have an increased risk if they:
- or their partner have a neural tube defect
- have had a previous pregnancy affected by a neural tube defect
- or their partner have a family history of neural tube defects
- have diabetes
In addition, women who are taking anti-epileptic medication should consult their GP for advice, as they may also need to take a higher dose of folic acid.
If any of the above applies to you, talk to your GP as they can prescribe a higher dose of folic acid. Your GP or midwife may also recommend additional screening tests during your pregnancy.
Vitamin D regulates the amount of calcium and phosphate in the body, these are needed to keep bones and teeth healthy.
You need to take vitamin D during your pregnancy to provide your baby with enough vitamin D for the first few months of its life. You should take a supplement of 10 micrograms of vitamin D each day when you are pregnant and if you breastfeed.
In children, not having enough vitamin D can cause their bones to soften and can lead to rickets (a disease that affects bone development in children).
Vitamin D can be found naturally in oily fish (such as salmon, mackerel and sardines), eggs and meat. Some manufacturers add it to some breakfast cereals, soya products, some dairy products, powdered milk, and fat spreads such as margarine.
The best source of vitamin D is summer sunlight on your skin. The amount of time you need in the sun to make enough vitamin D is different for every person, and depends on things such as skin type, the time of day and the time of year. However, you don't need to sunbathe: the amount of sun you need to make enough vitamin D is less than the amount that causes tanning or burning. If you have dark skin or always cover your skin, you may be at particular risk of vitamin D deficiency. Talk to your midwife or doctor if this applies to you.
If you are short of iron, you’ll probably get very tired and may suffer from anaemia. Lean meat, green leafy vegetables, dried fruit, and nuts contain iron. If you'd like to eat peanuts or foods that contain peanuts (such as peanut butter) during pregnancy, you can do so as part of a healthy balanced diet unless you're allergic to them or your health professional advises you not to. Many breakfast cereals have iron added. If the iron level in your blood becomes low, your GP or midwife will advise you to take iron supplements.
Vitamin C protects cells and helps keep them healthy. A balanced diet containing fruit and vegetables, including broccoli, citrus fruits, tomatoes, bell peppers, and blackcurrants, can provide all the vitamin C you need.
Calcium is vital for making your baby's bones and teeth. Dairy products and fish with edible bones – such as sardines – are rich in calcium. Breakfast cereals, dried fruit – such as figs and apricots – bread, almonds, tofu (a vegetable protein made from soya beans) and green leafy vegetables – such as watercress, broccoli and curly kale – are other good sources of calcium. You also need to know which foods to avoid.
Vegetarian, vegan and special diets
A varied and balanced vegetarian diet should give enough nutrients for you and your baby during pregnancy. However, you might find it hard to get enough iron and vitamin B12. Talk to your midwife or doctor about how to make sure you are getting enough of these important nutrients.
If you are vegan (you cut out all animal products from your diet), or you follow another type of restricted diet because of food intolerance (for example, a gluten free diet for coeliac disease) or for religious reasons, talk to your midwife or GP. Ask to be referred to a dietitian for advice on how to make sure you are getting all the nutrients you need for you and your baby.
Healthy Start vitamins in the UK
The UK Healthy Start scheme provides vouchers to pregnant women who qualify and families who qualify. The vouchers can be used to buy milk and plain fresh and frozen vegetables at local shops. You'll also get coupons that can be exchanged for free vitamins locally.
Healthy Start vitamin tablets for women are specially designed for pregnant and breastfeeding women, and contain vitamins C and D and folic acid.
Healthy Start children's vitamin drops are for infants aged from six months to five years old, and contain vitamins A, C and D.
If you qualify for the Healthy Start scheme you can swap your coupons for free vitamins locally – just ask your midwife or health visitor where they are accepted in your area. You can also use the Healthy Start postcode search to find where you can use the vouchers.
If you're not on the Healthy Start scheme, some NHS organisations still offer the vitamins for free or sell them – ask your midwife about local arrangements.
You qualify for Healthy Start if you’re at least 10 weeks pregnant or have a child under four years old, and you or your family get:
- Income Support
- Income-based Jobseeker’s Allowance
- Income-related Employment and Support Allowance
- Child Tax Credit (but not Working Tax Credit unless your family is receiving Working Tax Credit run-on only*) and has an annual family income of £16,190 or less (2012/13)
If you are pregnant and under 18 years old, you qualify for Healthy Start vouchers regardless of your income. *Working Tax Credit run-on is the Working Tax Credit you receive in the four weeks immediately after you have stopped working for 16 hours per week (single adults) or 24 hours per week (couples). You can download a Healthy Start application form at the Healthy Start website, or call the Healthy Start helpline on 0845 607 6823 and order a copy.
Other articles about preparing for pregnancy:
Nutrition in pregnancy - in detail - technical
Nutritional requirements for healthy pregnancy vary according to a woman’s prepregnancy nutritional state and her access to food during pregnancy: there is no unifying nutritional advice that is appropriate for all pregnant women throughout the world, or even within nations.
The well-nourished mother—maternal adaptation to pregnancy requires few dietary changes during pregnancy. She should eat one or two portions of sea fish per week to -ensure intake of n-3 long-chain polyunsaturated fatty acids sufficient to provide at least 200 mg of docosahexaenoic acid per day, which is needed for the healthy development of the fetal central nervous system. Supplemental folic acid (400 µg/day) during the first trimester reduces the risk of neural tube defects, but with this exception extra vitamins and micronutrients are not necessary for well-nourished, healthy pregnant women who eat a balanced diet, and excessive amounts of some micronutrients can actually be harmful to the fetus. Thiamine replacement is essential for women with hyperemesis gravidarum.
The chronically undernourished pregnant woman—needs a balanced diet that is supplemented with (1) vitamins—including folic acid, vitamins A, B1 (thiamine) and others; and (2) micronutrients—iron, zinc, iodine. and others, to ensure that the fetus fulfils its growth potential. However, although protein and energy supplements given to such women of small stature and pelvis size improve fetal growth and perinatal outcome, they can lead to obstructed labour, a significant cause of maternal and perinatal death in the developing world.
Overeating and obesity—pregnancy complications due to poor nutrition in high-income countries tend to follow from these causes. Those who gain excessive weight in pregnancy double their risk of a poor outcome and increase their likelihood of postpartum weight retention, and women who retain weight after their first pregnancy have an increased risk of gestational diabetes, pre-eclampsia, caesarean delivery, stillbirth, and large for gestational age babies in subsequent pregnancies. Obesity during pregnancy fuels obesity in the next generation.
There is no unifying nutritional advice that is appropriate for all pregnant women throughout the world, or even within nations. Nutritional advice must take account of maternal body size, lifestyle, and availability of food. In the developed world, where food is generally plentiful and obesity is more prevalent than undernourishment, dietary recommendations for a healthy pregnancy are often targeted to reduce excessive weight gain and pregnancy complications. By contrast, in nations where food is scarce, nutritional intake falls far below the average intake of women who eat to satisfy their appetite, and pregnancy adaptations—which are inevitably a compromise—attempt to maximize fetal growth. Micronutrients and vitamin supplements are given with good effect to chronically undernourished pregnant women in the developing world, but with few exceptions are unnecessary and can be harmful to well-nourished pregnant women in the developed world. Conversely, protein and energy supplements given to chronically malnourished pregnant women of small stature and pelvis size improve fetal growth and perinatal outcome, but can lead to obstructed labour, a major cause of maternal and perinatal death in the developing world.
The ability of pregnant women to adapt to different environmental and nutritional conditions is a key requirement for reproductive success. Gestational metabolic adaptations minimize extra nutritional requirements and optimize fetal growth. However, millions of pregnant women are unable to provide enough nutrition for their fetus to thrive despite these adaptations. Poor prenatal nutrition not only affects perinatal outcome, but also dictates susceptibility to adult diseases and even the health of the next generation.
The liberal availability of food can also be harmful when it goes unchecked. In the United Kingdom between 1990 and 2002–2004 the prevalence of obesity doubled amongst pregnant women attending for their first antenatal appointment. In 2002, almost half of all women in the United State of America of child-bearing age (20–44 years) were either overweight or obese, with a body mass index (BMI) of more than 25 kg/m2. A similar rise in the prevalence of obesity has been seen worldwide, including in many developing countries, and is associated with an increased risk of pregnancy complications.
Weight gain in pregnancy
During pregnancy, well-nourished mothers with free access to food gain up to 30% of their prepregnancy weight, of which only 25% is fetal. By contrast, mothers with limited access to food gain as little as 10% of their prepregnancy weight, of which up to 60% is fetal. Excess weight gain increases birth weight, but also increases the rate of caesarean section, pre-eclampsia and gestational diabetes mellitus. Poor weight gain increases the incidence of low birth weight (defined as <2500 g at term). A World Health Organization study of maternal anthropometry on 110 000 births from 20 countries found that best pregnancy outcome was associated with a full-term baby weighing 3.1 to 3.6 kg (mean 3.3 kg) and maternal weight gain of 10 to 14 kg (mean 12 kg).
In 1990 the Institute of Medicine in the United States refined these observations with guidelines for weight gain in pregnancy, adjusted according to prepregnancy maternal weight (Table 1 below). These recommendations remain appropriate despite many subsequent analyses: they minimize the overall risk of adverse pregnancy outcome for both mother and neonate. Obese women are least able to keep within these guidelines. Those who gain excessive weight double their risk of a poor pregnancy outcome and increase their likelihood of postpartum weight retention. Women who retain weight after their first pregnancy have an increased risk of gestational diabetes, pre-eclampsia, caesarean delivery, stillbirth, and babies that are large for gestational age in subsequent pregnancies. Furthermore, obesity during pregnancy fuels obesity in the next generation: about one-third of infants of obese mothers are in the 90th centile for their age, and a child of an overweight mother is three times more likely to be overweight by age 7 years.
Maternal undernutrition in the developing world
Nutrition during pregnancy and until a child is 24 months of age is most critical to its future growth and development. Maternal and child undernutrition is the underlying cause of 3.5 million deaths around the world each year, mainly of children. Eighty per cent of the world’s undernourished children live in just 20 countries, mainly in sub-Saharan Africa, and south-central and south-eastern Asia. In these countries 20 to 40% of women aged 15 to 49 years are undernourished (BMI <18.5 kg/m2). Chronically undernourished women are often of short stature, which increases their risk of an operative delivery due to cephalopelvic disproportion, and perioperative comorbidity is high even if caesarean section is available.
|Table 1 Recommended weight gain in pregnancy (adapted from recommendations of the Institute of Medicine of the United States)|
|Maternal BMI (kg/m2)||Recommended weight gain (kg)|
|Low (<19.8 kg/m2)||12.5–18|
|Normal (19.8–26.0 kg/m2)||11.5–16|
|High (26.1–28.9 kg/m2)||7–11.5|
|Obesity (>29 kg/m2)||<7|
BMI, body mass index.
In these low-income countries, 16% of babies are of low birth weight (<2500 g), of which more than two-thirds are due to fetal growth restriction and less than one-third are due to prematurity. In comparison, in high-income nations only 5% of babies are of low birth weight, of which most (55%) are premature. Low birth weight increases an individual’s risk of morbidity and mortality during all phases of life: neonatal, childhood, and adult.
Energy requirements during pregnancy
The rate of human fetal growth is slow and the daily incremental energy stress of human pregnancy is relatively low compared with that in other species. This allows a mother time to adapt her metabolism and energy expenditure to diverse nutritional conditions and the fetus to develop a complex brain. The total energy cost of pregnancy for a woman with a mean weight gain of 12 kg is 325 MJ (77 000 kcal). Energy requirements increase gradually as pregnancy progresses. In the first trimester an estimated 375 kJ (90 kcal)/day is required, in the second trimester 1200 kJ (287 kcal)/day, and in the third 1950 KJ (466 kcal)/day. Energy requirements during lactation are similar to those of the third trimester.
The three major components of energy expenditure in an average well-nourished pregnant woman are growth of the fetus and reproductive tissues (c.18%), new maternal fat stores (c.38%), and increased maternal metabolism (c.44%). Poorly nourished women try to maintain fetal growth by depressing their basal metabolic rate until late pregnancy and by laying down less fat. Although such adaptations usually result in successful reproduction, they are inevitably a compromise with regards to perinatal health. However, attempts to quantify minimal energy requirements for good perinatal health will always be confounded by huge individual variability and the practical difficulties of attributing a single nutritional component to morbidity, which is a multifaceted problem.
Well-nourished women increase their basal metabolic rate most rapidly after 16 weeks gestation until term. During the middle trimester large amounts of maternal fat are laid down as energy stores, although women with the highest cumulative rise in basal metabolic rate lay down the least fat. If food intake becomes limited during late pregnancy, maternal fat can be mobilized to support the period of most rapid fetal growth. A similar strategy of fat storage before anticipated energy expenditure is used by birds before they migrate and by mammals before they hibernate. Well-nourished women with free access to food rarely need to utilize all their fat stores to support late fetal growth, and excess fat remains difficult to lose postpartum. Even poorly nourished women with low gestational weight gain lay down some extra fat, but they also suppress their basal metabolic rate until late in pregnancy in order to support fetal growth.
Studies of well-nourished women have found that maternal energy intake actually increases by little more than 25% of that required to fulfil energy needs. It is likely that much of this estimated shortfall is due to under-reporting of nutritional intake, while some is made up by an economy of energy expenditure, including reduced physical activity and diet-induced thermogenesis.
Metabolic changes in pregnancy
The mechanisms that control the diverse metabolic responses to pregnancy are not fully understood.
Leptin, a protein produced by adipose tissue and the placenta, circulates in increasing amounts during pregnancy and controls peripheral energy status and body fat. Ob/ob mice (deficient in leptin) become insensitive to exogenous leptin when pregnant, consistent with the build-up of maternal fat stores until the last trimester, but a precise role for leptin during pregnancy remains to be elucidated. Leptin is integrated with the hypothalamo–pituitary–gonadal axis and may explain why thin women with low leptin levels remain infertile until they have adequate fat stores.
There is no need for pregnant women to increase their total dietary fat as a percentage of energy intake during pregnancy or lactation. The only change that is recommended is an increase in consumption of n – 3 long-chain polyunsaturated fatty acid (LC-PUFA) sufficient to provide at least 200 mg of docosahexaenoic acid (DHA) per day, which can be achieved with the consumption of one or two portions of sea fish per week. DHA is needed for the healthy development of the fetal central nervous system and several small studies have shown that it appears to improve pregnancy outcomes for mother and neonate. Concerns that large predator fish contaminated by neurotoxic levels of methylmercury might be harmful to the fetus are easily outweighed by the benefits of DHA. Limiting fish intake to smaller oily fish such as herring, mackerel, and salmon will further diminish this concern.
During the first half of pregnancy women produce more insulin in response to a glucose load and are more sensitive to exogenous insulin than in the nonpregnant state. These changes affect carbohydrate and lipid metabolism to favour increased fat production and storage. During the second half of pregnancy a woman becomes resistant to insulin, so that at term the action of a particular circulating concentration of insulin is 50 to 70% lower than in the nongravid state. As a consequence, the fat stores laid down in the first half of pregnancy are mobilized and postprandial blood glucose levels remain higher for longer. Circulating levels of fatty acids and glycerol increase and are used by the mother as an energy source in preference to glucose and amino acids, which are left for the fetus. As a consequence, fasting pregnant women oxidize fat and produce ketones far sooner than they do when they are not pregnant, and women with an exaggerated peripheral resistance to insulin are at risk of gestational diabetes mellitus.
Pregnancy is an anabolic state. Protein and nitrogen metabolism adapt early and gradually throughout healthy pregnancy to provide for tissue growth. Well-nourished women are estimated to accumulate an extra 500 g to 1 kg of protein during pregnancy, almost half of which is maternal lean body mass, whilst the rest lies within the fetus and reproductive tissues.
In the United Kingdom the advised increment of dietary protein has been calculated to increase gradually throughout pregnancy to 8.5 g/day at term, but this does not take into account reduced hepatic metabolism of branched chain amino acids and hence reduced urea synthesis. The rate of urea synthesis declines by 30% during the first trimester and by 45% during the third trimester, hence serum urea concentration falls, providing more nitrogen for protein synthesis.
Vitamins and micronutrients
In many parts of the developing world micronutrient deficiencies are endemic and have serious consequences for fetal, neonatal, and maternal well-being, e.g. hypothyroidism due to iodine deficiency and night blindness due to vitamin A deficiency. Such deficiencies are rare in developed countries.
Calculated increments in the recommended daily allowance of specific nutrients are derived from estimates of the cost of fetal growth and increased maternal metabolism. However, these calculations do not usually take account of maternal metabolic adaptations aimed to minimize the need for extra nutrients. For example, intestinal absorption of calcium increases in well-nourished women and the need for an increase in dietary calcium diminishes. Conversely, increased folic acid excretion leads to an underestimate of folic acid requirements. Furthermore, individual micronutrients interact with each other and changes to one may have a detrimental effect on the activity of another.
It is now widely accepted that supplemental folic acid (400 µg/day) during the first trimester reduces the risk of neural tube defects. With this exception, extra vitamins and micronutrients are not necessary for well-nourished, healthy pregnant women who eat a balanced diet. Indeed, excessive amounts of certain micronutrients can be harmful to the fetus. The situation is quite different for undernourished women of countries in the developing world.
Vitamin A is a lipid-soluble vitamin essential for healthy embryogenesis and fetal growth. Preformed vitamin A is found in dairy products and liver, the recommended daily allowance during pregnancy being 2000 to 2700 IU/day (670–899 retinol equivalents; RE). Vitamin A deficiency is endemic in some parts of the world and maternal vitamin A supplements of 6000 to 8000 IU/day (2000–2670 RE/day) result in a small increase in birth weight. However, excessive doses of vitamin A (>15 000 IU/day or 5000 RE/day) or supplements of more than 10 000 IU/day, are teratogenic, and drugs that are derived from vitamin A, such as the retinoids, are associated with an estimated 25-fold increased risk of fetal malformation. It is therefore recommended that the daily dose of vitamin A should not exceed 5000 IU/day (1665 RE/day) during pregnancy.
The carotenoids (β-carotene), which are precursors to vitamin A, do not appear to be teratogenic and are now being substituted for preformed vitamin A in multivitamin preparations. In general, vitamin A supplements are unnecessary for well-nourished women and potentially harmful to the fetus. Breast milk is rich in vitamin A, and is important for neonatal immunity.
Thiamine (vitamin B1)
Thiamine deficiency is endemic in some developing countries, but is also a global problem in women with hyperemesis gravidarum. Severe and persistent vomiting during pregnancy leads to thiamine deficiency and can cause Wernicke’s encephalopathy, hence thiamine replacement is essential for women with this condition.
Vitamins C and E
Serum vitamin C levels fall by about 50% during pregnancy, hence it was previously recommended that this was supplemented. Furthermore, the antioxidant properties of vitamins C and E were thought to reduce the risk of pre-eclampsia, but this is not the case. Indeed, at high doses (vitamin C 1 g/day and vitamin E 400 IU/day) these vitamins increase the risk of babies being born with a low birth weight and their supplementation is not justified in pregnancy.
More than 800 million people live in iodine-deficient areas. Inadequate dietary iodine leads to maternal hypothyroidism, which in turn is detrimental to in utero growth and development. Supplemental iodine, which is added to salt in most developed countries, can prevent these consequences.
Zinc deficiency is associated with intrauterine growth restriction and teratogenesis. Maternal zinc levels remain stable during pregnancy through increased intestinal absorption. Excess iron supplements, smoking, alcohol abuse, or subsistence cereal diets high in phytate can all inhibit zinc absorption: under such conditions pregnant women may benefit from 25 mg zinc daily.
During pregnancy expansion in plasma volume exceeds the increase in red cell mass, causing a fall in haemoglobin concentration. Healthy pregnant women not taking iron supplements drop their haemoglobin from 13.3 g/dl to 11.0 g/dl by 36 weeks gestation. The minimum incidence of low birth weight (<2500 g at term) and preterm labour is associated with maternal haemoglobin in the range 9.5 to 10.5 g/dl, which in the nongravid state would indicate anaemia, but supplemental iron is probably unnecessary in pregnancy unless the mean corpuscular volume is less than 84 fl. A meta-analysis of randomized controlled trials examining the benefit of supplemental iron found a significant reduction in the proportion of women with haemoglobin levels less than 10 g/dl, but no effect—beneficial or harmful—on maternal or fetal outcome.
Anaemia of multiple causes is endemic in many developing nations, and the risk of maternal death is increased with severe anaemia (haemoglobin <7.0 g/dl), a condition where supplemental iron is unlikely to have much effect. However, in such countries mild to moderate anaemia can be prevented with iron and folate supplementation and has improved pregnancy outcome, and multiple micronutrient supplements may be even more beneficial. Many developing countries advocate a policy of iron and folic acid supplementation for all pregnant women. More studies are necessary to monitor the effects of this policy on maternal and perinatal outcome.
The growing fetus gains about 50 mg calcium per day by mid pregnancy and about 300 mg/day at term, and the breastfed infant receives about 250 mg of calcium in breast milk each day. The recommended daily allowance of calcium during pregnancy and lactation is 1.2 g/day, but women with much less dietary calcium undergo metabolic adaptations to meet the demands of pregnancy and lactation without any detriment to their health or that of the fetus.
During pregnancy, maternal calcium absorption increases twofold, stimulated by increased 1,25-dihydroxyvitamin D (calcitriol) activity due to placental synthesis of calcitriol and increased renal 1α-hydroxylase activity. Although urinary calcium excretion doubles during pregnancy, fasting urinary calcium excretion, corrected for increased creatinine clearance, is unchanged. The concentration of parathyroid hormone falls during pregnancy, suggesting that the pregnant woman receives enough calcium for her growing fetus. There are two caveats: one is the pregnant adolescent who needs to meet the demands of her own growth as well as that of the fetus; the other is the benefit of supplemental calcium for women on a low-calcium diet, but not those on a normal calcium diet, to prevent pre-eclampsia.
Following delivery, circulating calcitriol concentrations return to nonpregnant levels. During the first 3 to 6 months of breastfeeding mineralization of the maternal axial skeleton declines by about 3 to 5%, recovering after 6 months whether or not breastfeeding continues. Calcium supplements of 1 g/day given to lactating women do not prevent bone demineralization or improve the calcium concentration of breast milk, even if the woman is on a low-calcium diet. Furthermore, repeated long periods of breastfeeding in women with a low calcium intake do not contribute to osteoporosis in later life.
Fetal programming - the influence of fetal nutrition on adult disease
Epidemiological studies have found that low birth weight due to intrauterine growth restriction, rather than prematurity, is associated with an increased risk of cardiovascular disease in adulthood. It is hypothesized that a poorly growing fetus makes metabolic adaptations in utero to optimize growth and development. Despite these physiological adaptations, driven in part by insulin-like growth factors, birth weight remains low, and because of them the individual is indelibly programmed to insulin-resistance syndromes that are detrimental to long-term cardiovascular health.
Animal studies have shown that the composition of maternal diet can influence fetal growth and consequently blood pressure in her offspring. At present not enough is known about the mechanisms that control human fetal growth to give maternal nutritional advice that might eventually reduce the risk of cardiovascular disease in her children. Understanding these mechanisms may help to ameliorate the global epidemic of cardiovascular disease.
Foods to avoid during pregnancy
Acute maternal infection with Toxoplasma gondii can cross the placenta to the fetus. Congenital infection is least likely during early pregnancy, but more severe when it occurs. The risk of congenital infection can be kept to a minimum by not eating undercooked meat, taking care whilst handling raw meat, and avoiding contact with cat faeces.
Food cravings during pregnancy
Common food cravings during pregnancy are for dairy products and occasionally for nonorganic material such as soil (pica). Common aversions are to alcohol, caffeine, and meats.