Your midwife will be watching your weight to ensure that it is gained at an appropriate rate. Lack of weight gain or a sudden burst of weight gain may concern her. Ideal weight gain does not mean you gain the same amount of weight every week. Most mothers only gain 2-4 pounds in the first trimester, begin gaining weight in the second trimester and may gain half a pound a week towards the end of pregnancy. Here is the breakdown of where that extra weight goes:
7.5 lbs, baby
1 lb, placenta
2 lbs, uterus
2 lbs, amniotic fluid
1 lb, breast tissue
2.5 lbs, increased blood volume
5 lbs, fat
6 lbs, tissue fluids
27 lbs, Total
Appropriate Weight Gain
The 2009 Institute of Medicine Guidelines for appropriate weight gain are based on pre-pregnancy BMI. Pre-pregnancy BMI is only an estimate, but it is used in the gestational weight gain studies and is an easy number to calculate, so can be used to help determine the optimum weight gain.
- BMI less than 18.5 : Gain 28-40 pounds
- BMI 18.5-24.9: Gain 25-35 pounds
- BMI 25-29.9: Gain 15-25 pounds
- BMI 30 or more: Gain 11-20 pounds
Women who gain more weight than is considered appropriate are at increased risk for cesarean, large for gestational age babies (this is four times more likely), and macrosomia. High gestational weight gain is the strongest predictor of maternal overweight and obesity postbirth, with the risk of weight retention increasing as the gestational weight gain increases. In women who have already had a baby, the risk for emergency cesarean and large for gestational age increase with increasing gestational weight gain.
Excessive gestational weight gain is also associated with an increased risk of childhood obesity. In studies of pregnant rats, the children of rats who were over-fed during pregnancy have a greater taste for junk foods and increased fat tissue deposition, which could mean they will need to work harder to stay a healthy weight throughout their lives.
Women who gain less than what is considered appropriate are at increased risk for small for gestational age babies and low birth weight. Low gestational weight gain may also increase the risk of preterm birth in underweight women.
Women who are overweight or obese have another challenge during pregnancy. While normal weight women have an increase in insulin secretion and sensitivity during pregnancy that increases fat accumulation, overweight and obese women do not have the rise in peripheral insulin sensitivity. This causes a more pronounced insulin resistance in late pregnancy, leading to a higher risk for gestational diabetes.
For women who are overweight or obese before pregnancy, the gestational weight gain is a less strong predictor of fetal growth, and healthy babies are born with lower gestational weight gains. Recent evidence shows the lowest prevalence of adverse birth outcomes occur when obese women lose weight during pregnancy. For overweight and obese women, the lowest rate of preterm birth occurs among women who gain the least.