Nutrition and Pregnancy: Why Weight Matters

Last week I talked about how it was important to not “eat for two” when you’re pregnant. One reason for that is that the amount of weight a woman gains while pregnant is important for her health and for the health of her child. It’s important to gain enough weight without gaining too much. Like Goldilocks, you want to aim for “just right.”
Part of this has to do with simple nutrition. If you aren’t eating enough, odds are you are missing out on some important nutrients. If you are eating too much and gaining a lot of weight during pregnancy, it’s possible that you’re gaining weight on foods that are high in sugar and fat.
But taking nutrients out of the equation, two elements of a healthy pregnancy are:
  • A woman’s body mass index (BMI) at the time of conception 
  • How much weight she gains during pregnancy 
As I mentioned last week, a pregnant woman needs more calories during pregnancy to support the growth of the fetus, the thickening placenta and uterine wall, as wells as meet the demands of expanding breast tissue and increasing blood volume. It’s also normal for women to gain some fat during pregnancy, as part of the body’s adaptation to create a good temporary home for the growing baby. This fat tends to deposit in the hips, thighs and arms.
When a woman doesn’t gain enough weight during pregnancy, there is an increased risk of:
  • Preterm birth 
  • Miscarriage or stillbirth 
  • Low birth weight (less than 5 pounds, 8 ounces) due to intrauterine growth restriction 
  • Smaller-than-normal head circumference (a sign of impaired brain development) 
When a woman gains too much weight during pregnancy, there is an increased risk of:
  • Gestational diabetes (diabetes during pregnancy) 
  • Gestational hypertension (high blood pressure during pregnancy) 
  • Pre-ecclampsia (this is very dangerous) 
  • High birth weight (above 8 pounds 13 ounces or 9 pounds 15 ounces, depending on the source) 
  • Difficult labor and delivery (if the baby is big) 
Babies that are low birth weight (small for gestational age or SGA) and babies that have a high birth weight (large for gestational age or LGA) are both at risk for future problems like type 2 diabetes and obesity, although for very different reasons.
A child who was deprived of nutrients and calories before birth may have an underdeveloped pancreas and kidneys, making them more prone to diabetes and high blood pressure later in life. Also, a child that was “programmed” to cope with deprivation before birth may easily gain excess weight in a world where for many of us, food is available all the time.
A child who received too many calories before birth may develop extra fat cells, making it easier to gain weight later in life. Because fat cells are very metabolically and hormonally active (they are not just storage depots), having too many of them can contribute to type 2 diabetes and other health problems.
Some of the risks of not gaining enough weight overlap with the risks of being underweight at conception. Accordingly, some of the risks of gaining too much weight overlap with the risks from being obese at the time of conception. Therefore, I would encourage every woman to plan for pregnancy and get as healthy as possible before conceiving. Since life doesn’t always work out that way, it is wise for all women to eat to support good nutrition and a healthy weight gain during pregnancy. This can minimize or even eliminate the risks linked to an less-than-optimal pre-pregnancy BMI.
After intensive examination of what is known and not known about how the health implications of a woman’s BMI at conception and weight gain during pregnancy, in 2009 the Institute of Medicine (IOM) revised their guidelines for pregnancy weight gain:
  • Women with a BMI less than 18.5 (“underweight”) should gain 28-40 pounds. 
  • Women with a BMI of 18.5-24.9 should gain 25-35 pounds. 
  • Women with a BMI of 25.0-29.9 (“overweight”) should gain 15-25 pounds 
  • Women with a BMI of 30.0 or more (“obese”) should gain 11-20 pounds. 
Since many women are concerned about losing their “baby weight,” I’ll mention this: the more weight a woman gains during pregnancy beyond the recommended range, the more likely she is to hold on to some of those pregnancy pounds a year or more after giving birth. If a woman has more children, and gains extra weight each time, the pounds she keeps can really add up. 
Next weeks: Key nutrients as pregnancy progresses