The maternal risks of obesity during pregnancy include intolerance to glucose during pregnancy, called gestational diabetes, and preeclampsia, a life-threatening condition of high blood pressure with possible kidney and placenta damage. Potential fetal risks related to maternal obesity include physical deformities, shoulder displacement during birth and childhood obesity. Restricting weight gain might reduce maternal and fetal complications. Although health care professionals may use several approaches to calculating calories, rate of weight gain is the final determinant to prenatal calories.
Guidelines
First trimester calories don't increase from prepregnancy needs regardless of initial pregnancy weight. Weight gain guidelines set forth in 2009 by the Institute of Medicine for an obese pregnancy, defined as a body mass index, or BMI, greater than 29.9, restrict weight gain to an average of 15 pounds with .5 pounds per week beginning in the second trimester. Pregnancy isn't a time to restrict calories, but the American Congress of Obstetricians and Gynecologists suggests supervised, hypocaloric diets to promote weight loss for pregnant women with BMIs greater than 39.9, which is morbid obesity.
Ratio Calculation
Using the U.S. Department of Agriculture’s dietary guidelines, a 5-foot-4 female requires 1,800 calories during the first trimester of pregnancy. The U.S. Department of Health and Human Services suggests 300 calories per day for a pregnancy with a normal BMI beginning in the second trimester, or week 14 of gestation. Pregnancy weight gain for women with normal BMIs is an average of 30 pounds. The ratio of calories to pounds is 300 calories divided by 30 pounds, which equals 10. Applying this ratio of 10 to the obese woman’s average weight gain of 15 pounds produces 150 calories. Adding 150 calories to the first trimester’s 1,800 calories produces 1,950 daily calories beginning in the second trimester.
Hamwi Calculation
Adopted by the American Dietetic Association in 1964, a tool for estimating ideal body weight, or IBW, is the Hamwi Method. For females, allow 100 pounds for the first 5 feet, plus 5 pounds for each additional inch. A 5-foot-4 female’s IBW is 100 pounds plus 5 times 4, or 20, for a total of 120 pounds. Certified diabetes educator and registered dietitian, Deborah Thomas-Doberson, suggests using 14 calories per pound of IBW in the first trimester and 16 calories per pound of IBW in the second trimester for obese pregnant women. First trimester calories for the 5-foot-4 female would be 14 times 120 for a total of 1,680 calories. Second trimester calories would be 16 times 120 for a total of 1,920 calories.
Rate of Gain
Reevaluating rate of weight gain happens with each prenatal visit. If rate of gain is less than .4 pounds weekly, prescribed calories might increase. If rate of weight gain is greater than .6 pounds per week, a decrease in daily calories is appropriate. However, increasing daily physical activity, such as walking, might slow down weight gain, avoiding the need to decrease calories.
References
- The American Congress of Obstetricians and Gynecologists: Pregnancy
- National Institutes of Health: Weight Gain During Pregnancy
- U.S. Department of Health and Human Services: Dietary Guidelines for Americans 2010
- National Institutes of Diabetes and Digestive and Kidney Diseases: Weight-Control Information Network
- RD 411.com: Ideal Body Weight and Adjustments for Adults
- Clinical Diabetes: Nutritional Management of Gestational Diabetes and Nutritional Management of Women With a History of Gestational Diabetes: Two Different Therapies or the Same
