A mother's pre-pregnancy weight and how much weight she gains during pregnancy both have a major effect on the size of her baby. While having too large a baby increases the baby's risk of becoming obese, it is equally important to reduce the risk of a low birth-weight infant. Too low a birth weight (less than 5 1/2 lbs) increases the risk of birth defects and other health problems. The optimal birth weight is now considered to be 7-10 lbs. Generally, the lower the weight gain in pregnancy, the lower the birth weight. This is true for all women - even overweight women. Underweight women need to gain the most weight during pregnancy and obese women the least.

• Ideal weight gain. A total weight gain of 25-35 lbs during pregnancy is desirable. Normally, only 3-6 lbs is gained in the first trimester (12 weeks). Thereafter, an average of 0.8lbs each week is normal.
  
  
• Excessive weight gain. Weight gain of over 35 lbs during pregnancy may result in too large a baby. A sudden increase in weight might result from toxemia or excess calorie intake. Dietary changes to control weight gains are best supervised by an obstetrician and dietitian. Pregnancy is not the time for extreme dieting as fetal growth can be impaired.
  
  
• Inadequate weight gain. Weight gain of less than 15 lbs is more likely to result in a low birth-weight baby. The past practice of over-restricting food intake to limit weight gains is no longer considered healthy for pregnant women. Too little weight gain, even in obese women, indicates that the dietary intake is too low to provide adequate nutrition for optimal development of the growing baby and the maintenance of mother's health.
  
  
• Teenagers are a high risk group for low birth-weight infants. Unlike older mothers, growing teenagers may need to “eat for two”. A weight gain of 30-35 lbs will minimize the risk of a teenager having a low birth-weight baby. Under no circumstances should a growing teenager view pregnancy as a time to lose weight.