This report provides brief overviews of the workshop speakers’ presentations and related deliberations and concludes with a set of emerging cross-cutting themes both for researchers interested in interdisciplinary work in this area and for those who are involved in developing strategies to promote appropriate weight before, during, and after pregnancy. The report should be viewed as only a first step in exploring opportunities to develop a synthesis of diverse research and applying this knowledge to promote appropriate weight in women of childbearing age, and it is confined to the material presented by the workshop speakers and participants. Neither the workshop nor this report is intended as a comprehensive review of what is known about maternal weight and gestational weight gain and maternal and child health outcomes, although it is a general reflection of the literature. Many additional contributors of gestational weight gain and health outcomes were not addressed in the limited time available for the workshop. A more comprehensive review and synthesis of relevant research knowledge will have to wait for further development.
Building from the initial presentations and deliberations, the committee has highlighted certain themes that are described below to help strengthen the direction and quality of future studies. One theme that arose early in the workshop was that the 1990 report of the Institute of Medicine (IOM), Nutrition During Pregnancy, was written at a time when concern was focused on insufficient gestational weight gain and concerns about low birth weight. In the intervening years, the larger context has shifted in light of increasing rates of obesity to create concern about too much weight gain
during pregnancy and subsequent retention of weight, which may contribute to increasing obesity postpartum. The committee did not attempt to develop conclusions or recommendations in this activity. Given the wide range of methodological differences in the relevant research literature, a more extensive effort would be necessary to develop a critical review and analysis of evidence-based findings.
GESTATIONAL WEIGHT GAIN AND BIRTH WEIGHT
Gestational weight gain is an important variable of interest that has been studied extensively but deserves further attention. Gestational weight gain has three components: (1) the products of conception—that is, the fetus, the placenta, and the amniotic fluid; (2) the fluids in the extra tissue gained by the mother to support the pregnancy; and (3) maternal reserves. Roughly 70 percent consists of the pregnancy components and 30 percent is thought to be attributed to maternal stores. The largest component of gestational weight gain is water, followed by fat (the most variable of all of the components in the literature), and finally protein.
Patrick Catalano described the pattern of gestational weight gain, which is curved during the first two trimesters and then appears to be linear in the last trimester. Longitudinal studies of changes in fat mass show that as lean women (prepregnancy percentage of body fat of less than 25 percent) go through pregnancy, they tend to gain more fat compared with women who are obese (prepregnancy percentage body fat greater than 25 percent).
The IOM recommendations for weight gain in pregnancy reflect the curve of normal weight gain: very low at 0 to 10 weeks, 7 lbs. at 10 to 20 weeks, 10 lbs. at 20 to 30 weeks (this is when fat is accruing in the mother), and by 30 to 40 weeks the pace of weight gain should slow down. According to the average fetal growth curve, until about 28 weeks (the beginning of the third trimester), the average fetus weighs about 2 lbs. From 28 weeks until term, there is a 5.5 lbs. increase in weight that reflects fetal growth. Taken together, about 7.7 lbs. of weight in late pregnancy is related to the fetus, placenta, and amniotic fluid, not specifically maternal weight.
Past efforts to advise women on weight for pregnancy (before, during, and after) have focused little attention on maternal obesity. Most of the concern has addressed low birth weight deliveries in addition to other maternal and infant outcomes. However, a large increase in birth weight, concomitant with the increase in maternal weight over the last decade, is contributing to a shift in thinking about weight gain patterns and risks. It is important to note that measurement of birth weight is a proxy for several key indicators, including fetal growth and length of gestation. Low birth weight has additional causes other than gestational weight gain.
GUIDANCE FOR MATERNAL WEIGHT AND GESTATIONAL WEIGHT GAIN
The pregnancy weight recommendations of Nutrition During Pregnancy, the 1990 IOM report, were a frequent target of comment and discussion throughout the workshop. Other recommendations for pregnancy-related health were also noted, including guidance from the National Heart, Lung, and Blood Institute (NHLBI), the Maternal and Child Health Bureau, and the Centers for Disease Control and Prevention growth charts for adolescents. However, the prominence of the IOM recommendations in the work of the presenters and discussants was apparent. Of main concern were the need to reconcile different body mass index (BMI) categories (IOM versus NHLBI), the utility of and compliance with the IOM recommendations, and possible modifications to them.
For different reasons, many speakers and discussants articulated the need to harmonize the BMI categories established by the IOM report, NHLBI, and others. The discrepancies were noted as challenges for both research (especially meta-analyses and cross-study comparisons) and clinical practice. The different BMI categories were also seen as a challenge to outreach efforts, as an apparent undermining of public confidence in the research and clinical community if apparently conflicting advice is disseminated.
Utility of and Compliance with IOM Recommendations
All speakers who presented data on weight gain patterns in reference to the IOM recommendations noted that only about one-third of women gained within the specified ranges during pregnancy; all others gained more or less weight than is recommended. It was not clear whether women reaching the recommended weight gain targets did so consciously or not, further raising questions about compliance (a similar point could also be made about missing the weight gain targets). Biologically, weight gain during pregnancy in a healthy woman is highly variable. A number of comments were made throughout the workshop about how to make the IOM recommendations more useful to women and to practitioners. Examples included further specification of special populations (obese, adolescents, other racial/ethnic groups) in terms of both target weight and BMI. Effective intervention methods are not understood.
The IOM Recommendations
Many comments were made about the need for further specification or modification of the existing IOM recommendations. The most commonly expressed view was that the recommendations needed to be updated, specifically for obese women and adolescents. This view was based on the history of the recommendations themselves, which were derived from research published before 1990 and did not consider the effect of weight gain on maternal outcomes of pregnancy. Given the sociodemographic changes seen in the population of pregnant women, many presenters indicated that revisiting the recommendations seems warranted. This effort should strive to link new recommendations directly to specific, and more diverse, pregnancy outcomes, especially since the incidence of low birth weight babies seems to be of less concern now than when the IOM recommendations emerged in 1990.
Several discussants also noted that more research is needed to investigate establishing recommendations (BMI cut-points) for pregnancy that reflect other health outcomes besides gestational weight gain and birth weight. For example, other maternal health outcomes could include postpartum weight retention, cardiovascular disease, and other metabolic issues; other child health outcomes could include obesity-related consequences (e.g., mental health, BMI, cardiovascular disease). There is a need to understand the risks and to maximize the benefits for mother and child.
Many related comments were definitional in nature—for example, clearly defining what components are included in gestational weight gain and determining when baseline weight should be taken (especially for multiparous women). There was also some discussion about adding gestational weight recommendations based on other indicators, such as abdominal girth, which are becoming strong predictors of negative outcomes.
The need to consider important subgroups within the general population emerged in several contexts. First, many studies show important interactions between predictor variables (socioeconomic status and education) and race/ethnicity, suggesting their importance generally but also underscoring implications for possible intervention efforts. When race/ethnicity is considered in the literature, major groups are underrepresented, including Asian, American Indian, and Hispanic groups. Similarly, the increasing rate of obesity has led to the emergence of a relatively new, and growing, group of women who are obese when they become pregnant. Finally, the discussion frequently led to consideration of adolescent pregnancy. Each
of these is discussed below. Collectively, this theme centered on the need to provide more clarity, guidance, and interventions based on an individual’s characteristics.
Diverse Racial/Ethnic Groups
Although researchers have become more likely to include racial/ethnic minorities in their studies, the effects by race and ethnicity are not always reported, and many studies do not conduct or report analyses looking for interaction effects with race and ethnicity. Across the studies reviewed in the course of the workshop, the influence of race and ethnicity is mixed, although certain relationships seems to emerge that could be more clearly communicated. For example, non-Hispanic black women retain more weight postpartum than white women in all BMI categories. Finally, research is emerging about cultural norms regarding pregnancy and weight that are not yet well understood.
Current consideration of pregnancy in adolescence and what guidance or interventions are appropriate for adolescent mothers with regard to obesity risk may need to be revisited. For example, the 1990 IOM recommendations suggest that very young adolescents gain up to the maximum of the range for their BMI. However, relative to older mothers, postpartum weight retention in young adolescents could be serious, as their lifetime weight retention risk may be far greater. For example, during the discussion, data presented about adolescent mothers suggested a relationship between adolescent growth during pregnancy and higher gestational weight gain and postpartum weight retention. In addition, many adolescent mothers (especially younger adolescents) would be expected to be gaining weight as part of typical development in the absence of a pregnancy. These biological factors, coupled with psychological and sociodemographic characteristics of adolescent mothers, make this a highly specialized population in need of focused attention.
Obese and Morbidly Obese Women
As obesity has increased generally, so has its incidence among women of childbearing age as well as among those who become pregnant. Obesity in women can cause serious pregnancy-related complications, but it can also be modified to improve birth outcomes. Additional attention is needed for the population of obese women who become pregnant. Several speakers
suggested that prepregnancy BMI is a possible target for promoting appropriate weight during pregnancy and postpartum. Concerns were raised about reducing or controlling weight either before or during pregnancy through weight cycling, intentional weight losses, and regains. A number of practical issues also arise, especially for morbidly obese patients and those who were morbidly obese but underwent bariatric surgery or similar procedures before becoming pregnant. For example, medical practice and equipment may need to be modified to accommodate very large women during pregnancy and especially during delivery. Finally, obese women with a range of medical conditions in addition to their pregnancy can face additional challenges in the management of their pregnancy.
Lactating and Nonlactating Women
In general, breastfeeding is typically encouraged, if not supported, postpartum, for varying durations. However, lactation status is not a clear variable in research on gestational weight gain. Data are limited on potential mediating or moderating effects of lactation on maternal postpartum weight, as well as child outcomes.
Throughout the workshop discussion, participants offered a number of theoretical frameworks, either explicitly or implicitly. The workshop was not intended to bring about consensus on theoretical stance, but each of them suggested important considerations in promoting appropriate maternal weight and maternal and child outcomes.
A number of speakers, discussants, and participants indicated that pregnancy is an event in the life course of the mother, yet few studies have integrated this approach into their designs. The clearest inclusion of the life-course consideration is in designs that incorporate parity. This has implications for research purposes as well as clinical practice. For example, data were presented showing the accumulation of weight following each birth, with the indication that weight gain in the first birth contributes to the prepregnancy weight in subsequent births, but the prepregnancy period for first-time mothers may be very different from that of mothers with children.
As discussed more fully in the context of interventions, the place and timing of a particular pregnancy in a woman’s life also has implications for the types of interventions that may be necessary as well as those that may be
feasible. Accounting for previous pregnancies is not the only consideration drawn from a life-course approach, however. A woman’s age during pregnancy and childbirth has implications for her weight, gestational weight gain, health, and possibly child health outcomes. Delayed childbirth is driven by sociodemographic factors, which themselves could play a role, directly or indirectly, in maternal weight and health (cardiovascular disease) and child outcomes that are not necessarily explained by gestational weight gain.
Several participants drew on a whole-person approach, one that considers weight, nutrition, and physical activity as components of maternal weight status, gestational weight gain, and child outcomes. It was noted that the 1990 IOM recommendations address weight only. In general, nutrition for pregnant and lactating women is currently focused on caloric intake, without specific attention paid to specific nutritional requirements or guidelines. Calorie intake and good nutrition intersect when women make specific food choices. In addition to nutrition guidance, weight control is also about physical activity. It is also important to understand the biological variability in women. Individual metabolism affects calorie and physical activity outcomes. Studies indicate that the appropriate and inappropriate physical activity during and immediately following pregnancy is not well understood. It is important to understand different cultural traditions regarding food and physical activity during pregnancy when incorporating these variables in interventions to control weight.
The discussions noted that, in addition to food and physical activity, other psychosocial issues are important to examine in addressing the impact of pregnancy and its contributions to women’s health. Although there are methodological problems in these studies of psychological factors, more research is needed.
Population and Individual Approaches
Several speakers noted the conflict between a population-wide approach and an individual approach, which focuses on specific cases. As with many areas of research and practice, this tension is exacerbated by large-scale studies that do not examine special populations or even individuals seen in a clinical setting. There is a need for guidelines, outreach, and education efforts driven by epidemiological research to be translated for practitioners treating individual women. In order to do this, more research is necessary to build a body of evidence about patterns in the general or selected populations that can be effectively communicated at the individual level.
INTERVENTION, OUTREACH, AND EDUCATION
Although one session of the workshop focused specifically on interventions or factors that affect appropriate weight during pregnancy and postpartum, the issues related to interventions came up repeatedly throughout the discussions. In general, few studies can be found in the literature that describe interventions for achieving appropriate weight before, during, and after pregnancy. Knowledge is therefore limited about appropriate study design, components, effective timing of interventions, and education and outreach. However, the discussion did produce some consistent themes that are highlighted below.
When to Intervene
A number of presenters and discussants commented on the importance of recognizing the timing of an intervention for achieving appropriate weight before, during, and after pregnancy. In some cases, this was driven by a general theoretical stance (i.e., the life-course approach discussed earlier) and in others it was driven by practical concerns. Advantages to intervening during the pregnancy were largely practical—a woman’s visits to her medical provider are a great opportunity for an intervention. There is some regularity of contact between the woman and the medical provider, allowing for easier implementation of clinical-based interventions. However, many speakers noted concerns about balancing intervention goals with concerns about safety for the mother and the fetus during pregnancy, especially in connection with a restricted diet or heavy exercise. By contrast, interventions prior to or after pregnancy can focus on the woman without the same level of concern about the fetus, so more intensity may be possible. However, once women leave the prenatal treatment period, they are not regularly seen by the medical provider, making implementation a challenge. Several speakers noted high dropout rates in postpartum interventions although Special Supplemental Food Program for Women, Infants, and Children or regular infant care visits are possible points of contact postpartum. Nearly all who raised the issue, however, expressed an ideal that provided intervention before, during, and after pregnancy.
Components of Interventions
There is movement toward comprehensive interventions to promote recommended weight gain during pregnancy that focus on diet and physical activity, rather than a single-component approach. Psychosocial approaches are not well understood. In addition, designs using goal-setting with accompanying feedback to the woman were also noted to be essential compo-
ents. Finally, although community-wide interventions were discussed and thought to be promising approaches, the very limited available research (one study) does not provide strong evidence for effectiveness.
Outreach and Education
Beyond specific interventions, attention was given to various outreach efforts to inform and educate women about weight, pregnancy, and health, addressed either to the medical community or to women in general as well as to pregnant or prepregnant women in particular. A number of speakers noted that pregnant women want information, yet they are reluctant to rely on information when it appears to be conflicting or ambiguous. The desire to provide useful information, for example, talking about nutritious food versus calories, was highlighted. A number of participants discussed how the media or a social marketing approach may or may not help in communicating information to women of childbearing age.
HEALTH CARE AND HEALTH SYSTEMS
Two themes arose during the discussion that concern health care and national health care systems. The first concerns the need for improved data collection systems to monitor maternal weight and weight gain during pregnancy and postpartum and report information on an epidemiological scale. The second focuses on practical implications of addressing maternal weight and weight gain during pregnancy and postpartum through health care systems in the United States.
Currently no national surveillance system exists for monitoring weight and weight gain for pregnant women, nor for newborns and mothers postpartum, that would allow for tracking, documenting, and studying weight gain before, during, and after pregnancy. Although some states are attempting to use birth certificate data for these analyses, these efforts are still in the minority, and the data they collect are not standardized. To establish a surveillance system, however, critical decisions must be made about the data to be collected, the methodology, and the frequency. At various points during the workshop, participants indicated the need to collect data not only on height and weight (the necessary components for calculating BMI) but also on abdominal girth (although this latter measurement may be of little practical use when obtained during pregnancy). Measuring gestational weight gain at different time points throughout pregnancy is also seen as important in studying the effects of weight on child and maternal outcomes.
Once the data needs are identified, concerns about the validity of measurement must be considered, including local variability in definitions as well as variation introduced by differing data collection techniques, such as direct measurement versus self-report.
The Health Care System and Pregnant Women
The health care system for pregnant women is constrained by the nature and scope of services that are provided (or at least those that are accessible) to most women. For many first-time mothers, their entrance into prenatal care comes after conception and their health care providers provide relatively little education and information. Small changes to medical records could help professionals adequately track gestational weight gain. The lack of guidance from providers is especially likely for women who are uninsured or who have inadequate health insurance. This limited access to obstetric care is coupled with lack of access to other professionals, such as nutritionists and medical paraprofessionals, who could play an integral role in weight control programs and interventions. Health care disparities in the quality and cost of services for pregnant women are a wide-ranging problem. Pregnant women who typically show strong commitment to providing the best pregnancy they can for their unborn child simply lack access to intensive, multifaceted care. More systems-level studies are necessary, therefore, to strengthen the training of and access to quality care providers.
New mothers experience a transition with the birth of their child in their relationship with the health care system. Generally they have more regular access to pediatric care postpartum than maternal care. Applying a life-course approach to women before, during, and after pregnancy, there is need for alignment in the health care system across different care settings to ensure continuity of care for mothers with regard to their weight. A number of participants in the workshop noted that the current disconnected system (i.e., there is often no continuity of care for the woman before, during, and after pregnancy or with the care for the infant and older child) places limitations on collaborative efforts to control obesity.
SCOPE AND GAPS IDENTIFIED BY INDIVIDUALS DURING THE WORKSHOP
This list, which is based on the workshop discussions, reflects the suggestions made by presenters, discussants, and other workshop participants in relation to the workshop’s task. It was prepared for the convenience of the reader. It should not be construed as representing recommendations or consensus statements.
Research and databases describing the distribution of maternal weight (prior to, during, and after pregnancy) among different populations of women (see Chapter 2).
There is no national surveillance system that exists to adequately monitor maternal weight prior to, during, and after pregnancy in all racial/ethnic groups and different populations of women (e.g., adolescents and women of short stature) in the United States.
No national representative data exist for some minority populations, including Asian, American Indian, Alaskan Native, and non-Mexican Hispanic women.
Postpartum weight retention data are limited. Data show non-Hispanic black women retain more weight postpartum than non-Hispanic white women in all BMI categories.
Data show an association of maternal prepregnancy BMI and a range of negative maternal and child health outcomes.
Data show a relationship between gestational weight gain and negative maternal and child health outcomes.
There are limited studies on the effects of pregnancy in adolescence.
Research available on the individual, community, and health care system factors that impede or foster compliance with recommended gestational weight guidelines (prior to, during, and after pregnancy) (see Chapters 3 and 6).
The biological and social predictors or determinants reviewed may help women comply with recommended weight and gestational weight guidelines prior to, during, and after pregnancy.
Data are limited on the individual, psychosocial, community-based, and health care and health care system factors reviewed that may help women comply with recommended weight and gestational weight guidelines during and after pregnancy. Data are especially limited on these factors and especially on the interactions of these factors.
Opportunities for Title V maternal and child health programs to help women of childbearing age to achieve and maintain recommended weight (prior to, during, and after pregnancy) (see Chapters 3 and 6).
Data show prepregnancy BMI is a direct determinant of gestational weight gain. In addition, other research shows other biological and social determinants appear to influence the amount
(insufficient or excessive) and composition of gestational weight gain.
Data are unclear about determinants of gestational weight gain among different populations of women.
Studies are limited on interventions to promote appropriate weight during and after pregnancy.
Presenters and discussants think a comprehensive intervention should be provided to promote recommended weight gain prior to, during, and after pregnancy rather than a single-component approach.
Future research and data collection efforts that could improve the efforts of Title V programs to support women from different racial and ethnic backgrounds in their efforts to comply with recommended weight guidelines and to improve their maternal health (see Chapters 2, 3, 4, 5, and 6).
Collect representative data on the distribution of maternal weight (prior to, during, and after pregnancy) in all racial/ethnic groups in the United States.
Additional research is needed to untangle the complex relationship of prepregnancy BMI (and other social and biological determinants) and gestational weight gain (rate and pattern of gain).
Additional research is needed to understand the influence of biological and social determinants of gestational weight gain on different populations of women.
Further research is needed on the effects of maternal weight and gestational weight gain (in combination and separate) on maternal and child health outcomes in all racial/ethnic and other populations of women (e.g., adolescents and women of short stature).
Further research is needed on comprehensive (rather than single-component) interventions to promote recommended weight gain prior to, during, and after pregnancy.
Although this report was prepared by the committee, it does not represent findings or recommendations that can be attributed to the committee members. Indeed, the report summarizes views expressed by workshop participants, and the committee is responsible only for its overall quality and accuracy as a record of what transpired at the workshop. Presentations and discussion during the workshop on maternal weight gain during pregnancy highlighted a broad array of research topics, data elements, clinical interventions, and systems of care issues that are relevant to the influence of
pregnancy weight on maternal and child health. Each of these areas revealed an evidentiary base that could contribute to in-depth analyses, but such studies are challenged by methodological limitations and gaps in the literature. Future efforts will need to draw on a variety of theoretical frameworks and special population studies as well as comprehensive epidemiological studies to shape clinical interventions and guidance for pregnant women in achieving healthy outcomes for all.
Institute of Medicine 1990 Nutrition During Pregnancy. Washington, DC: National Academy Press.