October 2009 Issue
Pregnancy by the Numbers — The IOM Updates Weight Gain Guidelines
By Elizabeth M. Ward, MS, RD
Today’s Dietitian
Vol. 11 No. 10 P. 46
Considering maternal overweight and underweight can pose risks to both mother and baby, women need guidance in gaining the proper number of pounds to ensure the healthiest outcomes possible.
Women who are expecting a baby or pondering a pregnancy are often curious, worried, or preoccupied about pregnancy weight gain. And those who have recently delivered a child may be concerned about shedding postpregnancy pounds.
Recently released recommendations by an Institute of Medicine (IOM) expert panel explain in detail how much weight women should gain during pregnancy and why.
What’s New in Pregnancy Weight Gain?
While they are the first guidelines of their kind in nearly 20 years, the new IOM recommendations for pregnancy weight gain do not differ dramatically from those in the IOM’s Nutrition During Pregnancy, which was published in 1990. In part, that’s because reviews of observational studies suggest that women who enter pregnancy at a normal body mass index (BMI) and gain weight within the ranges recommended in the 1990 IOM guidelines are more likely to have a good birth outcome than women who gain outside of the recommended ranges.1
What has changed in the years since Nutrition During Pregnancy is the prevalence of overweight and obesity among American women in their childbearing years, both of which pose potentially serious health problems. In the last two decades, prepregnancy BMI and excess gestational weight gain (GWG) have increased across all population groups. More than ever, women are entering pregnancy overweight, obese, and even extremely obese. Currently, 62% of the women in the United States who could become pregnant are overweight (BMI greater than 25 kg/m2) and 33% are considered obese (BMI of 30 kg/m2 or higher).2
The rise in overweight and obesity among women of childbearing age has prompted concern about maternal health, pregnancy outcomes, and children’s well-being. But that doesn’t diminish the concern about starting a pregnancy underweight. A low prepregnancy BMI is one of the strongest predictors of adverse pregnancy outcomes, such as preterm birth and fetal growth retardation.3 In one study, BMIs below 20 kg/m2 and above or equal to 35 kg/m2 were associated with the reduced probability of achieving pregnancy in women receiving assisted reproduction treatment.4
No matter what their prepregnancy BMI, research suggests that many women gain more or less than the recommended number of pounds in the 1990 IOM weight guidelines.1 This trend, along with higher prepregnancy BMI rates and other factors, contributed to a reexamination of weight gain recommendations for pregnant women and strategies for implementing them.
Starting Pregnancy From a Healthy Place
The IOM committee worked from the perspective that pregnancy-related weight begins before conception and continues through the first year postpartum. The ideal situation for any woman is conceiving at a healthy weight and gaining the right number of pounds for the subsequent nine months by eating a balanced diet that meets maternal and fetal nutrient needs.
More often than not, women who are capable of becoming pregnant will have higher-than-normal BMIs, which presents a variety of potential problems. Prepregnancy BMI between 19.8 and 26 kg/m2 is associated with a lower risk for preeclampsia, gestational diabetes, and cesarean delivery.1
Prepregnancy overweight and obesity also affect the risk of structural birth defects. A meta-analysis published in the American Journal of Obstetrics and Gynecology in 2008 found that maternal obesity is positively associated with an increased risk of a pregnancy affected by a neural tube defect such as spina bifida. Other evidence has found that women who are overweight at the time of conception are more likely to have a child affected by a structural defect such as spina bifida, as well as heart defects, anorectal atresia, hypospadias, limb reduction defects, diaphragmatic hernia, and omphalocele.5
Prepregnancy maternal obesity has implications for infant feeding, too. Women who began pregnancy obese (BMI of 30 kg/m2 or higher) were less likely to initiate breast-feeding than their normal weight counterparts (prepregnancy BMI of 18.5 to 25 kg/m2) and were less likely to maintain full breast-feeding at 1 month and 3 months.6 Increased maternal BMI and GWG have also been associated with higher fat mass in infants and subsequent overweight in children years after birth.7,8
The amount of weight women should gain during pregnancy is based on prepregnancy BMI and how many children they are carrying. Women with higher BMIs are advised to gain less; those with lower BMIs should put on more pounds with pregnancy. The new IOM guidelines for pregnancy weight gain rely on the World Health Organization’s cutoff points for categorizing BMI, which are summarized in Table 1.
Weight Gain Guidelines
Gaining weight within the recommended range for prepregnancy BMI reduces the risk of postpartum weight retention, cesarean delivery, and pregnancy-induced hypertension.1 While some studies suggest that excessive GWG increases the risk of gestational diabetes, the IOM removed gestational diabetes (and preeclampsia) from consideration because of the lack of sufficient evidence that GWG was a cause of these conditions.
Table 2 provides a summary of weight gain guidelines for singleton and twin pregnancies.
Weight Gain With Obesity
According to the committee’s report, although a record-high proportion of American women of childbearing age have BMI values in obesity class 2 (BMI of 35 to 39.9 kg/m2) and class 3 (BMI of 40 kg/m2 or higher), available evidence is insufficient to develop more specific recommendations for GWG among these women. While the 2009 guidelines recommend a specific, relatively narrow range of recommended gain (11 to 20 lb) for women who are obese (BMI of 30 kg/m2 or higher) that the 1990 version lacked, recent evidence suggests that gaining even less than the new recommended amounts results in healthy outcomes for mother and child.
One group of women (prepregnancy BMI of 30 kg/m2 or higher) who gained less than 15 lb had a significantly lower risk of preeclampsia, cesarean delivery, and large-for-gestational-age infants, and the risk for small-for-gestational-age infants was minimal.9 Another recent study of 232 subjects who were obese (BMI of 30 to 69 kg/m2) at the time pregnancy occurred found that women who gained less than 15 lb while taking part in a supervised nutrition counseling program during pregnancy were less likely to develop gestational diabetes or preeclampsia, undergo cesarean section, or have their labor induced. No side effects were reported during the study, which was published this year in The Journal of the National Medical Association, and the babies were born healthy and at a normal weight.
Recommended Rates of Weight Gain
There is no increased energy cost associated with the first trimester of a singleton pregnancy, according to the IOM. Weight gain during the first trimester is relatively minimal, ranging from 1 lb to nearly 41⁄2 lb.1 Some women may gain no weight because extreme nausea, vomiting, or fatigue prevents them from eating their normal diet, while others may add a few pounds to their frame because of increased hunger, fluid retention, or reduced physical activity.
Women who are pregnant with twins require an additional 500 kcal/day, starting in the first trimester, according to a 2006 Journal of the American Dietetic Association article. Research published in 1997 in the American Journal of Obstetrics & Gynecology suggested that weight gain before 20 weeks gestation is positively associated with birth weight in twins born at 28 weeks or after; the effect was more pronounced in underweight women and significantly less pronounced in overweight women.
Women who attempted weight loss prior to conception should stop their weight loss efforts once pregnancy is confirmed. It’s important to recognize that women with a history of disordered eating may be fearful of weight gain during pregnancy and to offer counseling with qualified healthcare professionals, such as therapists and RDs who specialize in disordered eating.
Once the second trimester starts, the baby’s growth begins in earnest, and gaining weight on a steady basis is a must for proper development and a normal birth weight. Children who are born too small, which can result from inadequate weight gain during pregnancy, are more prone to certain chronic conditions, including heart disease and diabetes, during adulthood.10
Generally speaking, women need to increase their caloric intake by 340 kcal/day during the second trimester and 450 kcal/day during the third for a singleton pregnancy, according to the IOM. As with total weight gain, a woman’s rate of weight gain during the second and third trimesters is based on her prepregnancy BMI.
Table 3 offers a summary of suggested rates of weight gain for a singleton pregnancy. The IOM report does not provide information about weight gain rates for twin pregnancies.
What if women miss the mark for recommended weight gain? If they’re off by just a few pounds either way, it probably won’t make much of a difference to their health or their child’s well-being. The IOM guidelines provide a range in each BMI category, suggesting that good outcomes are achieved with all different weight gains.
The Role of Nutrition Professionals
According to the Centers for Disease Control and Prevention (CDC), an estimated 62 million American women are in their childbearing years (ages 15 to 44), and the majority of them are overweight and probably consuming diets with one or more nutrient deficiencies. Whether or not they specialize in women’s health, RDs and other qualified health professionals should take the lead in helping women meet the goals of the new IOM report to ensure they have the healthiest babies possible and to foster maternal health.
The IOM report specifically states that a higher proportion of American women should conceive at a weight within the normal BMI range (18.5 to 24.9 kg/m2). Given the number of women who need to achieve a healthy weight, meeting this challenge requires preconceptual counseling that provides personalized advice about diet and physical activity. According to the IOM, helping women achieve a healthy weight before conception occurs may require a referral to a dietitian. It’s important to note that experts say preconception counseling about weight loss and weight control may need to include additional contraceptive services to avoid pregnancy while achieving a healthier prepregnancy BMI.1
Preconception counseling is the cornerstone for achieving optimal outcomes of pregnancy and improved health for mothers and their children.1 In 2006, the CDC issued “Recommendations to Improve Preconception Health and Health Care,” a report that details the goals of preconception care to improve pregnancy outcomes and foster maternal health. The report cites diet quality and weight control as important topics to discuss with women before pregnancy occurs. RDs are able to tailor preconception and prenatal diets to fit a woman’s needs, helping to manage chronic conditions such as diabetes, hypertension, overweight, and underweight.
Another goal of the IOM report is to have a higher proportion of women limit their GWG to the specified ranges for their prepregnancy BMI. The first step in helping women adhere to those ranges is letting them know that they exist, which requires educating healthcare providers and women alike about the appropriate number of pounds to gain.
Services, including counseling about diet and physical activity, should be offered to all postpartum women, according to the IOM. The intent is to help women eliminate postpartum weight retention and conceive again at a healthier weight, as well as improve their long-term health.
— Elizabeth M. Ward, MS, RD, lives in Reading, Mass., and is the author of several books, including Expect the Best: Your Guide to Healthy Eating Before, During & After Pregnancy.
References
1. Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, D.C: National Academies Press; 2009.
2. Ogden CL, Carroll MD, Curtin LR, et al. Prevalence of overweight and obesity in the United States. JAMA. 2006;295(13):1549-1555.
3. Neggers Y, Goldenberg RL. Some thoughts on body mass index, micronutrient intakes and pregnancy outcome. J Nutr. 2003;133(5 Suppl 2):1737S-1740S.
4. Wang JX, Davies M, Norman RJ. Body mass and probability of pregnancy during assisted reproduction treatment: Retrospective study. BMJ. 2000;321(7272):1320-1321.
5. Waller KD, Shaw GM, Rasmussen SA, et al. Prepregnancy obesity as a risk factor for structural birth defects. Arch Pediatr Adolesc Med. 2007;161(8):745-750.
6. Mok E, Multon C, Piguel L, et al. Decreased full breastfeeding, altered practices, perceptions, and infant weight change of prepregnant obese women: A need for extra support. Pediatrics. 2008;121(5):e1319-e1324.
7. Hillier TA, Pedula K, Schmidt MM, et al. Childhood obesity and metabolic imprinting: The ongoing effects of maternal hyperglycemia. Diabetes Care. 2007;30(9):2287-2292.
8. Oken E, Taveras EM, Kleinman KP, Rich-Edwards JW, Gillman MW. Gestational weight gain and child adiposity at age 3 years. Am J Obstet Gynecol. 2007;196(4):322.e1-322.e8.
9. Kiel DW, Dodson EA, Artal R, Boehmer TK, Leet TL. Gestational weight gain and pregnancy outcomes in obese women: How much is enough? Obstet Gynecol. 2007;110(4):752-758.
10. Barker DJP. Fetal origins of coronary heart disease. BMJ. 1995;311(6998):171-174.
Table 1: Criteria for Classifications of Prepregnancy Weight Status
Body Mass Index (kg/m2)
Underweight < 18.5
Normal 18.5 to 24.9
Overweight 25 to 29.9
Obese ≥ 30
— Source: Institute of Medicine
Table 2
If Prepregnancy BMI Is Gain This Amount Gain This Amount
(kg/m2) (singleton) (twins)
< 18.5 28 to 40 lbs Ask your doctor*
18.5 to 24.9 25 to 35 lbs 37 to 54 lbs
25 to 29.9 15 to 25 lbs 31 to 50 lbs
≥ 30 11 to 20 lbs 25 to 42 lbs
Assuming a 1- to 4.4-lb weight gain during the first trimester
*Insufficient evidence was available to make a determination.
— Source: Institute of Medicine
Table 3: Recommended Weekly Rate of Weight Gain for Singleton Pregnancies, Second and Third Trimesters
Prepregnancy Recommended Weekly Weight Gain Range
BMI (kg/m2) (lbs) (lbs)
< 18.5 1 1 to 1.3
18.5 to 24.9 1 0.8 to 1
25 to 29.9 0.6 0.5 to 0.7
≥ 30 0.5 0.4 to 0.6