Determining Optimal Weight Gain

7

Determining Optimal Weight Gain

INTRODUCTION

In this chapter, the approach used by the committee for arriving at its recommendations for rewrite of the current guidelines for weight gain during pregnancy is discussed. First, a brief discussion of the principles used by the committee to develop a strategy for making its recommendations is presented. following, former approaches for developing gestational weight unit gain ( GWG ) guidelines, including those detailed in the Institute of Medicine ( IOM ) ( 1990 ) report, but besides others, are discussed. The scheme used by this committee is then described in some detail, along with the results of applying this approach. last, the committee ’ second recommendations are detail and hash out .

PRINCIPLES USED TO DEVELOP A STRATEGY

As was the casing for the report, Nutrition During Pregnancy ( IOM, 1990 ), the committee used a conceptual framework to organize the evidence and identify a set of consequences for the short- or long-run health of both the mother and the child that are potentially causally related to GWG. These consequences included those evaluated in a systematic review of outcomes of parental weight gain prepared for the Agency for Health-care Research and Quality ( AHRQ ) ( Viswanathan et al., 2008 ) american samoa well as others based on data from the literature outside the time window considered in that report. The committee considered both the severity of these outcomes and their frequency in the population. To develop estimates of risk and frequency, the committee used data from the published literature and from extra, commission analyses ( see below ). The committee considered the incidences, long-run sequela, and service line risks of respective likely outcomes associated with GWG ( extra information about these outcomes appears in Appendix G ). Postpartum weight retention, cesarean delivery delivery, gestational diabetes mellitus ( GDM ), and pregnancy-induced high blood pressure or preeclampsia emerged from this march as being the most important maternal health outcomes. The committee removed preeclampsia from consideration because of the lack of sufficient evidence that GWG was a induce of preeclampsia and not fair a observation of the disease process. The committee besides removed GDM from consideration because of the miss of sufficient tell that GWG was a cause of this condition. Postpartum weight memory and, in particular, unscheduled primary cesarean delivery rescue were retained for far retainer.

Measures of size at parturition ( for example, small-for-gestational age [ SGA ] and large-for-gestational age [ LGA ] ), preterm birth and childhood fleshiness emerged from this process as being the most important baby health outcomes. The committee recognized that both SGA and LGA, when defined as < 10th percentile and > 90th percentile of slant for gestational age, respectively, represent a mix of individuals who are appropriately or inappropriately little or big. In accession, the committee recognized that being SGA was likely to be associated with deleterious outcomes for the baby but not the mother, while being LGA was likely to be associated with consequences for both the baby and the mother ( for example, cesarean delivery delivery ). The committee addressed this mix of outcomes in the approach used to develop its recommendations. importantly, although the Institute of Medicine report ( IOM, 1990 ) recognized a tradeoff between maternal and child health was recognized as a possible consequence of changing the weight-gain guidelines, evaluation of that tradeoff was not possible with the data then available. This committee made evaluating this tradeoff a central element of its process to develop raw guidelines while recognizing that, although the available data have increased, they are hush less than fully adequate for this purpose. In making its recommendations, the committee besides sought to recognize unintended consequences and to develop guidelines that are both feasible and potentially accomplishable. It is important to note that these guidelines are intended for use among women in the United States. They may be applicable to women in other grow countries ; however, they are not intended for function in areas of the worldly concern where women are well shorter or thinner than american women or where adequate obstetric services are unavailable .

DEVELOPMENT OF RECOMMENDED WEIGHT-GAIN RANGES

Guidelines for Gestational Weight Gain

As was the subject for the current guidelines for GWG, the committee chose to formulate the new guidelines with a range for each category of prepregnant BMI. This stove reflects the impreciseness of the estimates on which these recommendations are based, the reality that good outcomes are achieved with a range of weight gains, and the many extra factors that may need to be considered when making a recommendation for an individual charwoman. To develop these ranges ( listed in ), the committee proceeded as follows. Based on the available published literature ( Appendixes E and F ) arsenic well as the reports of its consultants ( Appendix G ), the committee ascertained the GWG measure or stove of GWG values associated with lowest prevalence of the outcomes of greatest concern ( i.e., the five outcomes identified earlier : ( 1 ) cesarean delivery delivery, ( 2 ) postnatal weight memory, ( 3 ) preterm birth, ( 4 ) small- or large-for-gestational senesce parentage, and ( 5 ) childhood fleshiness ). When weighting the tradeoff among these outcomes, the committee considered, within each class of prepregnant BMI : ( a ) the incidence or prevalence of each of these outcomes, ( boron ) whether the outcomes were permanent ( for example, neurocognitive deficits ) or potentially modifiable ( for example, postnatal weight retention ), and ( hundred ) the quality of the available data. The committee compared the resulting ranges with those developed in the quantitative risk analysis conducted by its adviser, Dr. Hammitt. finally, the committee considered how its recommendations might be accepted and used by clinicians and women. The committee intends these guidelines be used in concert with good clinical judgment ampere well as a discussion between the woman and her prenatal care provider about diet and exercise. If a womanhood ’ second GWG is not within the proposed guidelines, prenatal care providers should consider other relevant clinical attest, american samoa well as both the adequacy and consistency of fetal increase and any available information on the nature of excess ( for example, fatness or edema ) or inadequate GWG, before suggesting that the charwoman modify her model of system of weights gain. The safety of intentional system of weights loss during pregnancy among corpulent women has not been determined. therefore, precedence should be given to addressing weight-loss issues either preconceptionally or between pregnancies, not during pregnancy .

TABLE 7-3

New Recommendations for Total and Rate of Weight Gain during Pregnancy, by Prepregnancy BMI. In constructing these guidelines, the committee recognized that they fall within the class of personalized music. use of these guidelines will require standardize assessment procedures to inform clinical opinion a well as subscribe of accessory services ( for example, counseling on nutrition and physical activity ) or other interventions that might be deemed necessary to achieve the recommend levels of weight gain. therefore, the committee recognizes that full implementation of these guidelines may entail extra aesculapian expenses. The committee did not attempt to estimate the order of magnitude of these likely extra medical expenses .

Rate of Weight Gain

meaning women typically gain ~1–2 kilogram in the first trimester. According to the new recommend GWG values, convention burden women should gain ~0.4 kg per workweek in the moment and third base trimesters of pregnancy. scraggy women should gain slightly more ( ~0.5 kilogram per workweek ) and corpulence women slenderly less ( ~0.3 kilogram per week ) than this sum ( ). corpulent women should gain about ~0.2 kg per week ( ). These guidelines were constructed based on the assumption that GWG is linear during the second and third trimesters of pregnancy. The IOM ( 1990 ) report made a series of recommendations about how to implement its guidelines in the context of caring for an individual patient. As they remain appropriate, the committee endorses the key elements of these recommendations :

  1. Before concept, use coherent and reliable procedures to measure and criminal record in the medical record the charwoman ’ sulfur weight and height without shoes .
  2. Determine the charwoman ’ second prepregnancy BMI
  3. cautiously measure the charwoman ’ sulfur altitude without shoes and system of weights in light dress at the first prenatal visit using procedures that have been rigorously standardized at the web site of prenatal care. Use reproducible, dependable procedures to measure weight at each subsequent visit .
  4. Estimate the charwoman ’ s gestational age from the attack of her last menstruation or from an early ultrasound interrogation .
  5. At the initial comprehensive prenatal interrogation and together with the fraught woman, set a weight-gain goal based on pre-pregnant BMI and other relevant considerations and explain to the charwoman why weight unit gain is authoritative .
  6. Monitor the woman ’ s prenatal naturally to identify any abnormal practice of gain that may indicate a necessitate to intervene, displaying the results diagrammatically for the womanhood ( see Chapter 8 Figures 8-1 through 8-4 ). When abnormal acquire appears to be very quite than a solution of an error in measurement or commemorate, together with the woman test to determine the induce and then develop and implement corrective actions .

DISCUSSION OF THE NEW GUIDELINES

These newly guidelines differ from those issued in 1990 in two important ways. First, they are based on a unlike fix of shortcut points for prepregnant BMI. Compared to the cutoff points used in the 1990 guidelines, using the WHO guidelines reduces the proportion of the population in the scraggy and corpulent groups, as these groups are based on more extreme BMI values, and raises the symmetry of the population in the convention weight and fleshy groups, as these groups are based on wide ranges of BMI values. second gear, these new guidelines include a specific, relatively minute rate of recommend advance for corpulent women. Although this recommendation applies to all women with a prepregnancy BMI value ≥ 30 kg/m2, it reflects the preponderance of data available to the committee that cover women in fleshiness class I ( BMI 30.0–34.9 kg/m2 ) rather than fleshiness classes II and III. As noted in chapter 2, in the by two decades more american women of childbearing age have prepregnant BMI values in fleshiness classes II and III. unfortunately, only two studies provide data on women in these fleshiness classes ( Kiel et al., 2007 ; information contributed to the committee in reference with Nohr [ see Appendix G ] ), and few of the women studied gain < 5 kilogram. It is possible, based on the data collected in these investigations and compared to higher gains, that weight gains < 5 kilogram may be associated with a more favorable tradeoff among outcomes. however, the committee ’ second reappraisal showed insufficient evidence to recommend gains this low and was concerned about the potential for doing the type of harm that is associated with fetal growth limitation and ketonemia ( see Chapters 3 and 6 ). Ketonemia, which can occur with the accelerate starvation that is feature of pregnancy, may be more frequent with low weight gains. The committee recognized that women in fleshiness classes II and III may, without interposition, gain little during pregnancy and are able to manage their convention of dietary intake so as to avoid ketonemia and other problems. however, there is no testify to determine whether a road map for very gloomy weight advance during pregnancy among women in fleshiness classes II and III would be managed well enough by these women and their care providers to avoid ketonemia.

Although there is ample justification for continuing to structure the new guidelines according to maternal prepregnancy BMI, this approach is not without limitations. Maternal stature, for exercise, has farseeing been known to be a determinant of parentage weight among women with a narrower range of prepregnancy weight ( 40–80 kilogram ) than normally observed nowadays ( Tanner and Thomson, 1970 ). In addition, stature appears to be a stronger predictor than prepregancy BMI of GWG ( Straube et al., 2008 ). however, the research necessary to show that altitude or another attribute might be a superscript alternative to prepregnancy BMI for constructing guidelines for subgroups of fraught women has not been conducted. The committee based its guidelines, in function, on the presumption that the extensive, coherent experimental data that link GWG to fetal growth, as measured by SGA and LGA, a well as those that link GWG to post-partum weight retention are causal. The express results from randomized trials among undernourish women provide indications of this pathway in some cases ( Susser, 1991 ), as do results from more holocene but very little randomized trials designed to control surfeit weight derive ( see Chapter 8 ). The committee recognizes, however, that the dim-witted mannequin in which increased caloric inhalation increases maternal burden and maternal system of weights, in turn, increases fetal weight, is likely to be more complex—and may even be faulty. There are possible non-causal explanations linking GWG to fetal emergence, including diet typography, affecting both GWG and fetal growth independently, or shared familial determinants of GWG and fetal emergence, although none of these alternatives has been proven valid. consequently, in developing these guidelines, the committee determined that it would be prudent to consider the evidence linking inadequate GWG, specially in scraggy and normal burden women, with increased risk of SGA ; and the evidence linking excessive GWG, particularly in fleshy and corpulent women, with increased hazard of LGA and its consequences. As extra experimental data are generated to confirm or refute a causal interpretation of the evidence linking GWG and fetal growth, this reasoning may need to be revised. In contrast, the likelihood that the link from increased caloric consumption to increased GWG and, in turn, from increased GWG to increased postnatal weight retention is causal seems more certain. however, postnatal slant retention reflects not only GWG but besides maternal actions postpartum, including but not limited to changes in dietary consumption and physical activity associated with new motherhood ampere well as breastfeeding demeanor ( Baker et al., 2008 ). It is noteworthy that these guidelines are structured around GWG ranges associated with beneficial outcomes for both mother and baby. For exercise, women who are more refer with postnatal weight unit retention than with the birth of a small baby can choose to gain at the lower rather of the higher end of the compass for their prepregnancy BMI category. As american women of childbearing age have become heavier, the tradeoff between maternal and child health created by variation in GWG has become more unmanageable to reconcile than it was when prevention of SGA births was overriding and there was relatively low risk of excessive weight memory postnatal and childhood fleshiness with extra GWG. The attempt made by the committee to project the short- and long-run consequences of GWG for both mothers and their children so as to reconcile the trade-offs between them is a singular feature of speech of the work used to develop these new guidelines. For this determination, the committee used data from the NMIHS ( information contributed to the committee in reference with Herring [ see Appendix G, Part II ] ) to provide estimates for the probability of baby deathrate and datum from the danish National Birth Cohort ( Nohr et al., 2008 ) to provide estimates for the probability of postnatal burden retention related to GWG within each category of prepregnant BMI. Dr. Hammitt linked the data on postnatal weight retention to estimates of morbidity and deathrate associated with extra enate slant. similarly, data from the Growing Up Today Study ( Oken et al., 2008 ) and supporting studies ( see Chapter 6 ) were used to provide estimates of the risk of childhood fleshiness at ages 9–14 years related to extra GWG. The committee chose these three outcomes because they are quantitatively authoritative and their consequences could be estimated with available data. Dr. Hammitt used the literature presently available to calculate quality adjustments for each result, which resulted in quality-adjusted life-years ( QALY ) for comparison across outcomes ( information contributed to the committee in consultation with Hammitt [ see Appendix G, Part IV ] ). Although the results of this quantitative risk analysis by Dr. Hammitt provided general confirm for the GWG guidelines that the committee developed from published and commissioned research data needed to support a more complete and persuasive analysis were unavailable. In particular, more information is needed on associations between GWG and longer term parental outcomes, such as postnatal system of weights retentiveness and late generative officiate and health, and child health outcomes such as fetal growth restriction, child neurocognitive outcomes, and fleshiness. such data should include not entirely the frequencies of outcomes but besides the utilities associated with each then that allow quality adjustments could be calculated. overall, these guidelines are signally similar to those included in the IOM ( 1990 ) report. The research that has appeared since that publication ampere well as the committee ’ second commissioned analyses support the robustness of the prior recommendations. specifically, it remains genuine that, within a given prepregnancy BMI class, goodly women can deliver healthy infants at a relatively across-the-board scope of weight gain values. unfortunately, an already boastfully and increasing proportion of the population is gaining outside of the prior recommendations ( see Chapter 2 ), which is likely to besides be the font with these new guidelines. As a result, it is time to focus attention on helping women to adhere to these guidelines. If research on attachment is conducted with experimental designs of adequate statistical power, such studies could last provide causal evidence that gaining within these new guidelines results in superscript outcomes of pregnancy for both mother and baby .

FINDINGS AND RECOMMENDATIONS FROM THE COMMITTEE’S ANALYSES

Findings

The committee found that :

  1. The WHO cutoff points have been wide adopted for categorizing BMI among nonpregnant adults and should be used for categorizing prepregnancy BMI adenine well ; the committee found that these categories are besides acceptable to use for categorizing the prepregnancy BMI of adolescents .
  2. evidence from the scientific literature is signally clear that prepregnant BMI is an mugwump forecaster of many adverse outcomes of pregnancy. As a result, women should enter pregnancy with a BMI in the normal slant class .
  3. Although a record-high number of american women of childbearing old age have BMI values in fleshiness classes II and III, available attest is insufficient to develop more specific recommendations for GWG among these women .
  4. There are only restrict data available to link GWG to health outcomes of mothers and children that occur after the neonatal period .
  5. There is insufficient evidence to continue to support a change of GWG guidelines for african american women, women of short stature, or adolescents younger than 16 years of senesce .
  6. There is insufficient data with which to establish how much more slant women carrying multiple fetuses should gain beyond that recommended for women carrying singleton fetuses .
  7. The committee reaffirms the clinical recommendations in IOM ( 1990 ) for implementation of these guidelines .
  8. There is insufficient evidence to reject the possibility that racial/ethnic group modifies the association between GWG and important parental and child health outcomes .

Recommendation for Action

Action Recommendation 7-1: The committee recommends that relevant federal agencies, private voluntary organizations, and medical and populace health organizations should adopt these fresh guidelines for GWG and publicize them to their members and besides to women of childbearing historic period.

Recommendation for Research

Research Recommendation 7-1: To permit the development of improved recommendations for GWG in the future, the committee recommends that the National Institutes of Health and other relevant agencies should provide corroborate to researchers to ( a ) behavior studies to assess utilities ( values ) associated with short- and long-run health outcomes associated with GWG for both mother and child and ( boron ) include these values in studies that employ decision analytic frameworks to estimate optimum GWG according to category of parental prepregnancy BMI and other subgroups .

Additional Recommendation for Research

Additional Research Recommendation 7-1: The committee recommends that the National Institutes of Health and other relevant agencies should provide subscribe to researchers to conduct studies among women carrying multiple fetuses that link GWG to relevant health outcomes among both mothers and their infants .

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