During pregnancy, many of the habits a woman has taken for granted have to be re-evaluated as she realises that she has become responsible for shaping a new life. Some of the most important habits that deserve special consideration are those affecting the nutritional status of the mother-to-be and her developing foetus. Many studies have shown that a woman's diet during pregnancy has important effects on both the mental and physical development of the foetus and her own health as well.

Eating for two means more than taking double portions of dessert. At issue during pregnancy is diet quality, rather than quantity. A pregnant woman is responsible for providing the developing foetus with nutrients, the raw materials necessary for the creation of a new life. Needs for many nutrients increase substantially during pregnancy, while caloric needs increase by only 300 to 500 calories per day. In other words, there's still not much room for empty calories. Those calories need to be "spent" on food choices that provide the nutrients needed for foetal growth and to support the physical changes that accompany pregnancy.

People used to believe that the developing foetus was akin to a parasite that could take whatever nutrients it needed from its host, the mother. We now know this analogy is not accurate. While the placenta is capable of manufacturing some nutrients, such as glycogen and cholesterol, most nutrients are brought to the foetus by the mother's blood. If a nutrient is missing from her bloodstream, foetal development may be compromised. For example, if the amino acids needed for brain development are absent, brain growth is not normal.

Maternal malnourishment is a major cause of low birth weight. Babies who weigh less than 5.5 pounds at birth are 10 times more likely to be mentally impaired than bigger babies and have a much higher risk of illness and death. It's up to the mother to provide the best possible environment for her developing baby. The following are some of the nutrients considered especially vital to the growth of the foetus and the physiological changes occurring in the pregnant woman.

Amino acids are the stuff of which life is made. Daily protein requirements increase from 50 to 60 g/day during pregnancy. Pregnant women are advised to consume at least three servings of protein foods daily, in addition to their four servings of milk.

Both the foetus and the mother need iron to make red blood cells. It is almost impossible to obtain the 30 mg of iron per day required during pregnancy from food alone, so iron is a recommended prenatal supplement.

Folic acid is a vitamin required for cell division and development of the foetal nervous system. Research has shown that a woman who receives extra folic acid a month before conception and for the first few months of foetal development has a much lower risk of giving birth to a baby with neural-tube defects such as spina bifida. Folic acid requirements during pregnancy are 400 to 800 ug per day, and because of its importance, folic acid is another recommended prenatal supplement.

Calcium is needed for the growth of bones and teeth. Blood calcium level is regulated by a number of hormones, so its level remains fairly constant. If dietary calcium is insufficient, calcium will be released from the mother's bones. That's why a woman is advised to consume four servings of milk and dairy products daily during pregnancy. Women who don't like milk often learn to disguise it in custards and milk-based soups. Teenage mothers, especially those who are still growing themselves, need six milk servings per day.

Although fiber is not considered a nutrient, an adequate intake of fiber is important during pregnancy to prevent constipation. Constipation typically increases because of the action of progesterone, which relaxes smooth muscle, and compression of the colon by the growing uterus. Iron supplements, often prescribed during pregnancy, frequently contribute to constipation.

As metabolic rate and blood volume increase, so does a woman's need for fluids. Six to eight glasses daily are recommended. Fluid intake should be even greater in hot environments and if the pregnant woman is exercising.

A woman's usual eating practices are often disrupted by pregnancy. Hormonal changes may cause nausea and vomiting ("morning sickness") during the first three months. Since little weight gain occurs during the first trimester, many women don't realise how much the embryo is growing and assume good nutrition is not yet a concern. Even though the embryo is still very tiny, good nutrition is as important as ever. Many women find that many small snacks work better than big meals and manage to get some good nutrition that way.

Toward the end of the pregnancy, the stomach becomes compressed as the uterus pushes up against the diaphragm, and big meals become impossible. Five or six small but nutritious meals usually work best during this time.

Weight gain is often a concern during pregnancy. While medical authorities generally suggest a weight gain of about 25 pounds, weight gain varies a great deal. Recent research looking at weight gain among normal-weight women experiencing healthy pregnancies and giving birth to healthy babies suggests that the upper limits of weight gain may be closer to 35 pounds. In one such group, 75% of the women gained more than 25 pounds. The median weight gain was 33 pounds, and about 25% of the women gained more than 40 pounds with no negative health effects for either the mother or baby. In contrast, women who gain relatively little weight are at risk of delivering low-birth-weight babies.

What happens to the extra weight after delivery? One study found that on the average mothers ended up only 2.2 pounds heavier after the pregnancy. Many obstetricians now feel that the energy spent worrying about weight gain should be replaced with a concern for nutritious food intake.