Pregnancy is not a good time to attempt weight loss, as the health of the growing fetus is placed at risk.

• Inadequate energy intake could “starve” the fetus of nutrients, especially in the third trimester, and increase the risk of a low birth weight baby.
  
• Excessive weight loss can produce ketones, a by-product of fat breakdown that may be detrimental to the baby's development.
  
• The mother runs the risk of ill-health both during pregnancy and in subsequent years. For example, inadequate calcium will increase the risk of osteoporosis (brittle bones) in later years.
  
• Unbalanced nutrition during pregnancy can severely affect milk production during lactation. Adequate protein and energy is required for optimal growth of the mammary glands. Even adequate nutrition during lactation may not overcome the lack of mammary gland growth that occurred during pregnancy.

Healthy eating habits acquired during pregnancy and breast feeding can form the basis of any necessary weight loss program after the birth of the baby. If a mother breast feeds her baby for at least 4-6 months, she will find that by 12 months her weight should return to pre-pregnancy levels.

Moderate exercise during pregnancy is beneficial. Swimming and walking are excellent forms of physical activity that are unlikely to overstress the body. Very strenuous activity is not advised as it may divert oxygen from the fetus to the exercising muscles. Lifting and carrying heavy objects should also be avoided. If any health problem is present, do not exercise without medical advice.

During pregnancy extra iron is required for the increase in mother's blood volume and for normal growth of the fetus and placenta. Since it can be difficult to get the recommended amounts of iron from food, a daily supplement is prescribed during the 2nd and 3rd trimesters. The extra iron promotes adequate stores in the mother to be used in breast feeding.

Folate is required for the production of new cells in the fetus and placenta. A folate supplement is usually given in conjunction with iron.

Excess alcohol can deplete the body of essential nutrients and can also cause defects in the fetus and lead to fetal alcohol syndrome. It is strongly advised to abstain from alcohol during pregnancy.

Cigarette smoking can constrict blood vessels supplying the placenta and reduce the nutrient supply to the growing baby. Smoking will also reduce oxygen supply to the developing baby and harm his or her health. Do not smoke while pregnant.