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Keywords:

  • gestational weight gain;
  • guidelines;
  • obesity;
  • pregnancy;
  • prenatal care

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References

The impact of the obesity epidemic on women of childbearing age has been of particular concern in recent years as a result of studies linking maternal weight status to long-term adverse outcomes for obese mothers and their offspring. The US Institute of Medicine developed new gestational weight gain guidelines based on this literature that attempts to strike a balance between the known risks and benefits of weight gain during pregnancy. More studies that include large numbers of obese women, examine outcomes beyond the perinatal period, and identify safe and effective pregnancy weight gain interventions are needed before lower weight gain recommendations can be made for obese women.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References

The World Health Organization (WHO) formally recognized obesity as a global epidemic in 1997, and by 2008 an estimated 500 million adults worldwide were reported as obese.[1, 2] The prevalence of obesity continues to rise in industrialized nations and, in many cases, developing nations are observing even more rapid increases. Furthermore, a large proportion of the global disease burden is attributed to the rise in obesity because of its pervasiveness relative to other risk factors and the diversity of its associated health consequences. Its impact on women of childbearing age has been of particular concern in the past decade due, in part, to an improved understanding of the role maternal weight status plays in the health of subsequent generations.

In the United States, the prevalence of obesity among adult women has more than doubled since the 1970s, but the rate of increase has slowed considerably in the past decade.[3, 4] According to the National Health and Nutrition Examination Survey (NHANES), a surveillance system designed to monitor the health status and behaviors of adults in the United States, the age-adjusted prevalence of obesity among adult females ≥20 years of age rose from 16.5% during the 1976–1980 survey period to 33.2% during the 1999–2002 survey period.[3, 5] In contrast, the prevalence increased by less than 3% between the 1999–2002 and 2009–2010 survey periods.[4, 5] Although nearly all subpopulations have experienced increases, the obesity burden has not been evenly distributed across racial/ethnic groups. Among women aged 20–39 years, the prevalence was greatest among non-Hispanic black women (56.2%) compared to Hispanic (34.4%) and non-Hispanic white (26.9%) women.[4] Of additional concern is the prevalence of obesity among adolescent girls approaching childbearing age. The prevalence of obesity among US females aged 12–19 years is estimated at 17.1%, and the racial/ethnic trends in this age group mirror those observed in adult women.[6]

In the context of the obesity epidemic in the United States, the US Institute of Medicine (IOM) developed new gestational weight gain guidelines in 2009 based on the most recent literature available.[7, 8] The revised guidelines differ from those issued in 1990 by providing a weight recommendation specifically for obese women and, in general, using prepregnancy weight status categories that are aligned with the WHO definition. Despite recommending a lower weight gain for obese women, the report was criticized by some healthcare providers who believe the recommendation is still too high for this subgroup.[9] However, given that women who are overweight and obese prior to pregnancy tend to exceed even the 2009 IOM weight gain recommendation, widespread adoption of successful interventions will be needed in order to shift the weight gain distributions downward for these groups as well as to meet the new guidelines and to warrant their further revision. The present article briefly reviews the evidence that led to the 2009 IOM weight gain guidelines, describes lessons learned from intervention studies which may help achieve targeted weight gains, and outlines where the scientific community needs to focus its energies in order to refine the guidelines for the future.

Evidence Underlying the 2009 IOM Weight Gain Guidelines

  1. Top of page
  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References

Obesity is known to play a role in the causal mechanisms of many adverse outcomes that may influence a woman's reproductive health, including reduced fecundity and fertility, hypertension, sleep disorders, and some cancers.[10] The health risks associated with obesity are further compounded during pregnancy when excess weight poses additional risks to the mother as well as risks to the infant. Pregravid obesity is associated with increased risk of pregnancy complications (e.g., gestational hypertension, preeclampsia, gestational diabetes mellitus, thromboembolic diseases), intrapartum outcomes (e.g., cesarean delivery), and fetal and infant outcomes (e.g., fetal macrosomia, late fetal death, birth defects, early neonatal death).[11] Obese women also retain more weight and are at greater risk of postpartum anemia. Furthermore, for infants born to mothers who were obese before pregnancy, the protective effects of breast milk may be eliminated or diminished because these mothers are less likely to initiate breastfeeding and tend to breastfeed for shorter durations.[12, 13] Given the potential consequences of carrying excess weight during pregnancy, achieving optimal weight gain becomes critically important for pregnant women.

In addition to prepregnancy weight status, maternal gestational weight gain is an important determinant of health for the mother and her offspring. Studies conducted between 1990 and 2007 in the United States show that more than 40% of women gained weight excessively and between 30% and 40% achieved a weight gain that was within the recommended range according to the 1990 IOM gestational weight gain guidelines.[14] The Agency for Healthcare Research and Quality (AHRQ) funded a systematic review of 150 studies that assessed the short- and long-term effects of maternal weight gain on maternal and infant outcomes.[14] Among the report's key findings was a strong association between high maternal weight gain and increased fetal growth, birth weight, and postpartum weight retention. The review also confirmed that gaining too little weight during pregnancy can be problematic. Low maternal weight gain was associated with poor fetal growth, lower birth weight, and an increased risk of preterm birth. The evidence in support of an association between gestational weight gain and childhood weight status was considered weak at that time. However, recent publications add further support for an association between gestational weight gain and childhood weight status.[15-18] The AHRQ systematic review served as the scientific basis for the IOM committee's 2009 report that reevaluated the gestational weight gain guidelines. The committee considered all the evidence from the systematic review in its deliberations, followed a conceptual model, and for the first time considered balancing the short- and long-term risks for the mother and infant in determining the appropriate weight gain ranges. This latter part was done by commissioning analyses in which outcomes were evaluated simultaneously for women with varying classes of obesity, which extended previously published work, and through a quantitative analysis of risk trade-offs between maternal and child health outcomes associated with gestational weight gain.[7]

The weight gain guidance provided by the IOM is individualized to the woman's pregravid BMI (Table 1). It is important to note that the amount and rate of weight gain for obese women was primarily based on data from women in the BMI range of 30–35 kg/m2, i.e., obesity grade I. Women with a BMI > 35 kg/m2 who were receiving good prenatal care and appropriate nutritional counseling may be able to gain less weight, but at the time of the report, and still today, there was insufficient evidence to make this a public health guideline for all obese women.

Table 1. Gestational weight gain recommendations by maternal prepregnancy body mass index.
Prepregnancy BMITotal weight gainRate of weight gain in the 2nd and 3rd trimesters
PoundsKilogramsPounds per week (range)Kilograms per week (range)
Adapted with permission from Institute of Medicine (2009).[7]
Underweight (<18.5 kg/m2)28–4012.5–181.0 (1.0–1.3)0.51 (0.44–0.58)
Normal-weight (18.5–24.9 kg/m2)25–3511.5–161.0 (0.8–1.0)0.42 (0.35–0.50)
Overweight (25.0–29.9 kg/m2)15–257–11.50.6 (0.5–0.7)0.28 (0.23–0.33)
Obese (≥30.0 kg/m2)11–205–90.5 (0.4–0.6)0.22 (0.17–0.27)

A graphic comparing gestational weight gain during 2002–2003 using Pregnancy Risk Assessment Monitoring System (PRAMS) data from multiple states to the 2009 weight gain recommendations highlighted the gaps that exist for helping women achieve the targeted weight gains for their respective weight groups.[7] The median weight gain among underweight and normal-weight women is close (within ±2.0 lb) to the midpoint of the range of recommended weight gains for their respective weight classes, although the distribution is shifted slightly downward for underweight women and is wider than recommended (with some weight gains exceeding the upper limit) for normal-weight women. The biggest gaps, however, are observed among women who are overweight and obese prior to pregnancy. The median weight gain for these women exceeds the midpoint of the recommended range by 10 lb for overweight women and 9.5 lb for obese women. Similar evidence was found from other population-based data sources. Thus, the results of the IOM 2009 report concluded there is a great need for randomized trials to help women gain weight appropriately given the associations between gestational weight gain and several maternal and child health outcomes.[7]

Studies Published After the 2009 IOM Guidelines

  1. Top of page
  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References

Since the release of the updated gestational weight gain guidelines in 2009, there has been an increase in the number of published articles describing weight gain patterns for women from various countries, socioeconomic levels, and obesity classes.[19-30] According to the Pregnancy Nutrition Surveillance System (PNSS), which monitors health status and nutrition indicators in low-income women enrolled in select public programs in the United States, the gestational weight gain distribution has remained fairly constant over time in this population.[31] In 2010, 21.5% of PNSS-eligible women gained less than the recommended amount of weight based on these guidelines, 30.6% gained within the recommended amount of weight, and 48% gained more than the recommended weight. However, overweight (58.8%) and obese (55.6%) women were significantly more likely to gain more than the recommended amount of weight than underweight (26.2%) and normal-weight (38.6%) mothers. One recent US study examining gestational weight gain by obesity class included several, but not all, perinatal outcomes considered in the IOM 2009 report and concluded that obese women with a BMI > 35 kg/m2 can gain no weight, or even lose weight, without having a significant detrimental effect on perinatal outcomes.[20] A large cohort study of women with gestational diabetes mellitus also found improvements on several maternal and neonatal health indicators among women who lost weight during the third trimester of pregnancy; however, their infants had a higher risk of preterm birth and of being small for gestational age.[32]

Studies of gestational weight gain conducted in Canada and Mexico and utilizing the 2009 IOM guidelines have also been published. In fact, Canada formally adopted the updated IOM gestational weight gain guidelines soon after their release.[33] Kowal et al.[34] published the first study of gestational weight gain trends by weight class using the newly adopted guidelines with data from the 2006–2007 Canadian Maternity Experiences Survey. According to that survey, the weight distribution of Canadian women delivering singleton, live infants was as follows: 6.1% underweight, 59.4% normal weight, 21% overweight, and 13.5% obese. These mothers gained an average of 15.8 kg; however, the proportion of women gaining inadequate or excessive weight during pregnancy varied significantly by prepregnancy body mass. Women who were underweight prior to pregnancy gained an average of 17.4 kg, which was more than any other BMI group, but the greatest proportion of women with excessive weight gain was observed among women who were overweight prior to pregnancy. The distribution of maternal weight gain also varied significantly by maternal age, ethnicity, and education level. To our knowledge, there are no ongoing, nationally representative surveillance systems that collect data on weight gain in pregnant or postpartum women in Mexico. It is possible, however, to gain some insight on trends in gestational weight gain from hospital- or community-based studies. For example, in a recent study of women seeking prenatal care for singleton pregnancies at the National Institute of Perinatology in Mexico during 2007–2008, 17% of normal-weight women gained above the recommended amount of weight compared to 35.7% of overweight women and 22.4% of obese women. The odds of poor maternal outcomes including gestational diabetes mellitus, preeclampsia, and lack of spontaneous initiation of labor were greatest for obese women in the sample.[35]

Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies

  1. Top of page
  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References

Intervention studies have provided some information about potential mechanisms that help women achieve a healthy weight before, during, and after pregnancy. Interventions during the interconception period generally aim to help women achieve a healthy weight prior to a subsequent pregnancy to decrease their risk of recurrent or new pregnancy complications associated with being at a higher weight status. Since weight loss during pregnancy is not recommended, interventions during pregnancy focus on helping women gain the proper amount of weight based on their prepregnancy weight status.

There are two major types of weight loss interventions during the interconception period: lifestyle (or behavioral) interventions and medical interventions. The results from lifestyle interventions are mixed, yet some studies have demonstrated modest success in helping women lose weight or achieve a healthy weight following pregnancy.[36] On the other side of the spectrum, bariatric surgery is a highly successful weight loss intervention available to those women who are the most severely affected by obesity and its associated consequences. Studies comparing perinatal outcomes of offspring born pre- versus post-surgery have reported 1.5- to 6-fold decreases in the prevalence of preeclampsia.[37] One Canadian study also reported a 3-fold decrease in severe obesity as well as greater insulin sensitivity and improved lipid profiles among children born post-surgery compared to their siblings born prior to surgery.[38]

In a systematic review of 88 articles reporting the results of lifestyle interventions during pregnancy, Thangaratinam et al.[39] concluded diet, exercise, and combination (diet plus exercise) interventions can be effective in helping women lose weight during pregnancy. The most success, however, was observed in diet-only interventions, which were also effective in decreasing a woman's risk of poor obstetric outcomes (e.g., gestational hypertension, preeclampsia, shoulder dystocia). Additionally, there was strong evidence that neither diet nor physical activity interventions increased the risk of low birth weight or being small-for-gestational age.

In another recent systematic review, Brown et al.[40] found that five gestational weight gain intervention studies incorporating goal-setting into the program design were successful in significantly restricting weight gain among all intervention group members compared to controls. Furthermore, the majority of these studies exhibited high retention rates, which is encouraging for future studies in this field. On the other hand, due to the wide variability in the interventions examined in this, and interventions of a similar nature, in general, it is unclear which program aspects are responsible for the weight management success in pregnant women.

Refining Weight Gain Recommendations: Next Steps

  1. Top of page
  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References

There is a need for more high-quality, randomized trials of lifestyle interventions in preconceptional and pregnant women. In particular, studies should investigate combined nutrition and exercise programs especially targeted to obese women. Current studies often include normal-weight and overweight mothers who may differ from obese mothers in important ways that may influence adherence.[36, 39, 40] It is clear that intervention strategies should consider stages of change, tailored messaging, social cues, and the built environment as well as responsiveness to food reward and an individual's food reinforcement; evidence is growing that the latter two domains may be important in motivating behavior change.[41] The evidence also supports the need for frequent interaction and components that address parenting skills and the stressful lives women lead. These types of studies are often best implemented by an interdisciplinary team of professionals.

While there is a need for studies that include larger numbers of obese women, it is important that the outcomes examined go beyond the perinatal period, such that the risks are balanced between the health of the mother and index child, especially given the growing evidence of fetal imprinting due to nutritional exposures in the intrauterine environment.[42] Furthermore, without knowing how obese women were able to lose weight, it is important to question the public health impact of such a recommendation. Strategies such as long periods of time without food and the use of laxatives or other types of weight loss medications may pose long-term health risks to the mother and child. Until there is proof of safe and effective interventions that can be provided to obese women under the care of a prenatal provider and that can achieve lower weight gain recommendations, blanket public health recommendations for all obese women should be avoided. “Public health recommendations must do no harm” was the basic premise of the 2009 IOM weight gain committee[7] and is a key element of the public health field.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References

Obesity among women of childbearing age is a major public health issue warranting additional studies that investigate its impact on short- and long-term maternal and child outcomes as well as best practices for weight management during pregnancy. In an attempt to strike a balance between the risks and benefits of weight gain during pregnancy for the mother and her offspring, the IOM Committee developed new gestational weight gain guidelines that recommend women in this weight class gain the minimum amount of weight necessary for the developing fetus. The recommendation was based on the best scientific evidence available at the time of the report and new evidence does not support a recommendation for weight loss during pregnancy for women of any weight class. The evidence in this area is, however, lacking, and future studies should seek to overcome current limitations in the literature by including large numbers of obese women, examining outcomes beyond the perinatal period, and identifying safe and effective ways to achieve weight loss during pregnancy.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Funding

Dr. Siega-Riz has received support from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (HD37584, HD39373), the National Institute of Diabetes and Digestive and Kidney Diseases (DK61981, DK56350), the National Institute of Health General Clinical Research Center (RR00046), and the Carolina Population Center for her work on maternal obesity and gestational weight gain.

Declaration of Interest

The authors have no relevant interests to declare.

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  2. Abstract
  3. Introduction
  4. Evidence Underlying the 2009 IOM Weight Gain Guidelines
  5. Studies Published After the 2009 IOM Guidelines
  6. Achieving Targeted Gestational Weight Gain Goals: Lessons from Intervention Studies
  7. Refining Weight Gain Recommendations: Next Steps
  8. Conclusion
  9. Acknowledgments
  10. References
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