INTRODUCTION — Both maternal prepregnancy body mass index (BMI) and gestational weight gain influence maternal and pediatric outcomes. For example, women who are obese (BMI ≥30 kg/m2) have a heightened risk of developing many complications in pregnancy, notably gestational diabetes and preeclampsia, and are more likely to have a cesarean delivery. Excessive gestational weight gain can have similar effects and increases the mother's risk for postpartum weight retention and becoming obese or developing worsening obesity, which can have adverse effects on her long-term health. The long-term effects of maternal obesity and excessive gestational weight gain on her offspring are also a concern. (See "Overweight and obesity in adults: Health consequences" and "Obesity in pregnancy: Complications and maternal management", section on 'Offspring'.)
On the other hand, women who are underweight (BMI <18.5 kg/m2) when they conceive and have inadequate gestational weight gain are at increased risk for delivery of a small for gestational age infant, which can have both short- and long-term consequences. (See "Infants with fetal (intrauterine) growth restriction".)
Guidelines regarding appropriate levels of weight gain in pregnancy have been promoted worldwide . Although the importance of appropriate prepregnancy weight and gestational weight gain is well established, many women begin pregnancy overweight, and many gain too much weight during pregnancy [2-4].
This topic will discuss issues relating to gestational weight gain in pregnancy. A detailed discussion of pregnancy issues in women who are obese can be found separately. (See "Obesity in pregnancy: Complications and maternal management".)
PHYSIOLOGIC WEIGHT GAIN — Physiologic weight gain during pregnancy can be attributed primarily to the weight of the developing fetus and to increases in maternal body water and fat. On average, weight gain at term is distributed as follows:
●Fetus – 7 to 8 lb (3.2 to 3.6 kg)
●Fat stores – 6 to 8 lb (2.7 to 3.6 kg)
●Increased blood volume – 3 to 4 lb (1.4 to 1.8 kg)
●Increased extravascular fluid volume – 2 to 3 lb (0.9 to 1.4 kg)
●Amniotic fluid – 2 lb (0.9 kg)
●Breast enlargement – 1 to 3 lb (0.45 to 1.4 kg)
●Uterine hypertrophy – 2 lb (0.9 kg)
●Placenta – 1.5 lb (0.7 kg)
DOCUMENTATION OF TOTAL GESTATIONAL WEIGHT GAIN — Gestational weight gain is the weight gained during pregnancy, which is rarely measurable with precision. The starting weight is often considered the weight documented at the first prenatal visit, but a self-reported or documented periconceptional weight may be used, especially if prenatal care is initiated after the first trimester . The ending weight is often considered the weight at the last prenatal visit, which is typically within days of delivery in late pregnancy but may be two to four weeks before a preterm delivery. Weighing the patient on the labor and delivery unit may be an option when an accurate rate is clinically important.
RECOMMENDATIONS FOR GESTATIONAL WEIGHT GAIN
Background — In 1987, the Committee on Nutritional Status During Pregnancy and Lactation of the Institute of Medicine (IOM, now National Academies of Sciences, Engineering, and Medicine [NAM]) made a detailed analysis of all published data pertaining to prepregnancy weight, weight gain during pregnancy, and pregnancy outcome and, based on this analysis, formulated recommendations for healthy gestational weight gain in 1990 . These recommendations were an attempt to increase the likelihood of a favorable pregnancy outcome, which was defined as delivery of a term live-born infant with a birth weight between 3000 and 4000 grams.
The IOM concluded that prepregnancy body mass index (BMI) was an important predictor of birth weight, independent of maternal weight gain, and that prepregnancy BMI should be used to guide recommendations for gestational weight gain. Thus, determining BMI became an integral part of the physical examination of pregnant women.
The IOM initially focused on low birth weight, assuming that increasing maternal weight gain among underweight women would reduce the rate of low birth weight and its associated perinatal morbidity and mortality, without adversely affecting other obstetric outcomes. In the absence of definitive data, 1990 IOM guidelines recommended what the authors considered an optimum weight gain for women with a normal BMI (25 to 35 lb [11 to 16 kg]), with lower weight gain for women beginning pregnancy at higher BMIs (with no upper limit) and higher weight gain for women beginning pregnancy at lower BMIs. The studies on which the 1990 recommendations were based were generally not of high quality; thus, more research was needed to validate or modify these guidelines.
In 2009, the IOM modified the 1990 guidelines based on findings from research performed over almost two decades following their initial recommendations. The updated IOM guidelines included recommendations for gestational weight gain in twin pregnancy, changes to the recommendations for obese women, and a recommendation that all women strive to be within the normal BMI range when they conceive . The World Health Organization (WHO) criteria using BMI for defining weight categories were adopted in the revision, as well. The updated recommendations were still based on observational data, and focused on some but not all relevant clinical outcomes. While robust data were available for small for gestational age and large for gestational age deliveries, cesarean delivery, and postpartum weight retention, available data for gestational diabetes and preeclampsia risk were not considered adequately robust to be included.
2009 IOM weight gain recommendations — The following recommendations are for the general obstetric population in the United States and are independent of age, parity, smoking history, race, and ethnic background because the relationship between weight gain and pregnancy outcome has not been evaluated extensively in subpopulations of pregnant women, and further study is needed. For example, teenagers may benefit from higher weight gain , and studies have suggested that women with class II or III obesity may benefit from lower weight gain target ranges than women with class I obesity (table 1) [9-12].
•BMI <18.5 kg/m2 (underweight) – Weight gain 28 to 40 lb (12.5 to 18.0 kg)
•BMI 18.5 to 24.9 kg/m2 (normal weight) – Weight gain 25 to 35 lb (11.5 to 16.0 kg)
•BMI 25.0 to 29.9 kg/m2 (overweight) – Weight gain 15 to 25 lb (7.0 to 11.5 kg)
•BMI ≥30.0 kg/m2 (obese) – Weight gain 11 to 20 lb (5 to 9.0 kg)
•BMI <18.5 kg/m2 (underweight) – No recommendation due to insufficient data
•BMI 18.5 to 24.9 kg/m2 (normal weight) – Weight gain 37 to 54 lb (16.8 to 24.5 kg)
•BMI 25.0 to 29.9 kg/m2 (overweight) – Weight gain 31 to 50 lb (14.1 to 22.7 kg)
•BMI ≥30.0 kg/m2 (obese) – Weight gain 25 to 42 lb (11.4 to 19.1 kg)
The recommendations in twin pregnancies were considered provisional because of the lack of data about the consequences of gestational weight gain on longer-term health outcomes. There were insufficient data on which to base recommendations for weight gain in triplet and higher-order multiple gestations or for the three classes of obesity.
Subsequent data that may inform guidance for gestational weight gain
LifeCycle Project weight gain recommendations — In 2019, the LifeCycle Project-Maternal Obesity and Childhood Outcomes Study Group performed an individual participant-level meta-analysis using data from over 196,000 singleton pregnancies within 25 cohort studies from Europe and North America that addressed relationships between gestational weight gain and clinical outcomes . In this study, the total gestational weight gain ranges associated with lower risks for adverse outcomes (preeclampsia, gestational hypertension, gestational diabetes, cesarean delivery, preterm birth, small or large size for gestational age at birth) are shown in the table (table 2).
The larger maximum weight gain in class III versus class II obesity likely reflects the relatively small number of women in these categories and the lack of statistical power to achieve more precise ranges.
The 2009 IOM guidelines were written in the absence of adequate published data to allow evaluation of relationships between gestational weight gain and preeclampsia or gestational diabetes and did not provide recommendations for pregnant women with different degrees of obesity (classes I, II, III). The LifeCycle study addressed these omissions and has the added strength of utilizing pooled individual patient data from many countries.
A key finding of the analysis was that prepregnancy BMI was more strongly associated with adverse maternal and infant outcomes than gestational weight gain. In particular, for almost all gestational weight gains, women with class III obesity had a greater overall risk for any adverse outcome than women with class II obesity, and women with class II obesity had a greater overall risk for any adverse outcome than women with class I obesity (eg, for weight gain ≥16 kg, the overall risks for any adverse outcome for women with class III, class II, and class I obesity were 79, 64, and 43 to 56 percent, respectively).
Although ranges of gestational weight gain associated with optimal outcomes in each obesity category were developed, the predictive power of gestational weight gain for the different adverse pregnancy outcomes was either low or moderate. These findings challenge the clinical usefulness of the ranges and suggest that prepregnancy BMI, particularly prepregnancy obesity, is a more important target for intervention than gestational weight gain.
US population data 2011 to 2015 — A retrospective cohort study including nearly 16 million mother-infant dyads linked birth and infant death data in the United States between 2011 and 2015 to assess the association between gestational weight gain (standardized to 40 weeks) and the outcome "serious infant morbidity (assisted ventilation, newborn intensive care unit [NICU] admission, surfactant therapy, antibiotic therapy, seizures) and mortality" . As in other large studies, women in the normal weight BMI class had the lowest rates of infant morbidity and mortality (8 and 0.28 percent, respectively) and women with class III obesity had the highest rates of these outcomes (12.4 and 0.58 percent, respectively).
The authors proposed the following gestational weight gain ranges as optimal for these infant outcomes:
●Underweight and normal BMI: 26 to <53 lb (12 to <24 kg)
●Overweight BMI: 22 to <44 lb (10 to <20 kg)
●Class I obesity: 18 to <35 lb (8 to <16 kg)
●Class II obesity: 13 to <35 lb (6 to <16 kg)
●Class III obesity: 13 to <22 lb (6 to <10 kg)
Gestational weight gain less than these proposed lower boundaries or weight loss had a greater impact on infant mortality among underweight and normal BMI individuals compared with individuals with obesity, but the latter also experienced increased rates of infant mortality when weight gain was not optimal.
The lower boundaries of the optimal gestational weight gain ranges proposed to minimize infant morbidity and mortality were higher than the lower boundaries proposed by IOM recommendations for overweight BMI (22 versus 15 lb [10 versus 7 kg]) and for obesity BMI: class 1 obesity (16 versus 11 lb [8 versus 5 kg]), and classes 2 and 3 obesity (13 versus 11 lb [6 versus 5 kg]). Of note, IOM recommendations were not stratified by class I, II, and III obesity (ie, lower boundary 11 lb [5 kg] for all three classes) and were targeted to optimizing pregnancy outcomes such as low birth weight, rather than "serious infant morbidity and mortality." The relationship between lower minimum gestational weight gain and increased infant morbidity and mortality in this study may be a marker of pathologic maternal factors, rather than causal. For the higher classes of obesity, further study is needed to clarify the relationship between gestational weight loss, gain, and maintenance and the risk of important adverse infant outcomes.
Novel research on caloric intake — The IOM guidelines, in common with the American College of Obstetricians and Gynecologists and the National Institute for Health and Care Excellence guidelines for weight management in pregnancy, recommend that all pregnant women modestly increase their caloric intake. At diagnosis of pregnancy or the first prenatal visit, pregnant women are often advised that caloric intake does not need to increase in early pregnancy as weekly weight gain in the first trimester should be minimal (1 to 4 lb [0.45 to 1.8 kg]). In the second and third trimesters, underweight and normal weight women are often advised that caloric intake needs to increase by approximately 300 calories per day to achieve 1 lb (0.45 kg) weight gain per week; for overweight and obese women, less of an increase is needed as weight gain should be approximately 0.5 lb (0.23 kg) per week (table 3). As a result of this guidance, derived from studies in nonobese women, the majority of intervention studies have been reluctant to suggest a reduction in energy intake in obese pregnant women.
Traditional guidelines for energy intake, as applied to pregnant obese women, have been challenged by a detailed investigation of the relationship between energy intake (primary outcome), energy expenditure, energy balance, and gestational weight gain in 54 obese pregnant women . Rather than estimate energy intake from self-reported food frequency questionnaires (a method often confounded by underreporting), energy intake over the second and third trimesters was directly determined by the energy intake-balance method, which is calculated as the sum of mean energy expenditure across pregnancy assessed by the gold standard doubly labeled water method and energy deposition in fat and fat-free tissues by plethysmography and isotope dilution. Energy expenditure was estimated during sleep by whole body calorimetry.
Thirty-six of the women demonstrated excessive weight gain by IOM guidelines for women with BMI ≥30 kg/m2; 8 achieved gestational weight gain within the recommended range, and 10 did not achieve the recommended weight gain. In women who achieved gestational weight gain within the recommended range, energy intake was less than energy expenditure. By contrast, for those whose weight gain was excessive, energy intake exceeded expenditure by 186±29 kcal/day, and this was associated with an increase in maternal adiposity, not fetal growth. As the difference was not explicable on the basis of diet or activity, nor related to markers of metabolic function or diet quality, the authors concluded that the metabolic demands of pregnancy are not increased in the second and third trimesters of pregnant women who are obese. Rather, they suggest that the energy requirements are met by mobilization of fat stores.
These important new observations cannot translate into clinical practice until appropriately powered intervention studies that actively encourage a reduction in energy intake are undertaken and confirm that any observed reduction in energy intake does not adversely affect clinical outcomes. However, in contrast to the small study described above, accurate measurement of energy balance cannot be achieved in a large study and proxy measures may be inaccurate. Nevertheless, advising pregnant women with obesity to reduce energy intake may be a more effective message than the "softer" advice for consuming a healthy diet and increasing activity, which most previous trials recommended in order to align with clinical guidelines.
RELATIONSHIP BETWEEN GESTATIONAL WEIGHT GAIN AND PREGNANCY OUTCOME
Weight gain above IOM target range
Pregnancy outcomes — Gestational weight gain above the Institute of Medicine (IOM) target range has been associated with an increased risk of macrosomia and large for gestational age (LGA) infants , cesarean delivery , pregnancy-related hypertension (gestational hypertension, preeclampsia) [17-21], and gestational diabetes [22,23], but not stillbirth . The magnitude of some of these relationships was illustrated in a 2017 systematic review that evaluated this issue (23 cohort studies, 1.3 million women): 47 percent of women exceeded the upper limit of IOM-recommended weight gain, and 23 percent did not achieve the lower limit of IOM-recommended weight gain . Compared with women with gestational weight gain within the recommended range, high gestational weight gain was associated with:
●Lower risk of preterm birth (odds ratio [OR] 0.77, 95% CI 0.69-0.86; absolute risk difference [ARD] -2 percent, 95% CI -2 to -1). As above, weight gain was not adjusted for gestational age, potentially resulting in less total gestational weight gain than would have been otherwise attained. Spontaneous and induced preterm birth were not clearly differentiated.
●Lower risk of small for gestational age (SGA; OR 0.66, 95% CI 0.63-0.69; ARD -3 percent, 95% CI -4 to -2).
●Higher risk of LGA (OR 1.85, 95% CI 1.76-1.95; ARD 4 percent, 95% CI 2-5).
●Higher risk of macrosomia (OR 1.95, 95% CI 1.79-2.11; ARD 6 percent, 95% CI 4-9).
●Higher risk of cesarean delivery (OR 1.30, 95% CI 1.25-1.35; ARD 4 percent, 95% CI 3-6).
There were several limitations in the available data, notably inclusion of few studies from the developing world; inconsistent definitions of preterm birth, cesarean delivery, and macrosomia; inclusion of studies published before the 2009 IOM guidelines (thus, with somewhat different gestational weight gain target ranges); and inability to evaluate gestational diabetes mellitus as an outcome.
Postpartum outcomes — Gestational weight gain above IOM target ranges can have long-term effects on both the mother and offspring. For offspring, it has been associated with an increased risk of neonatal adiposity [25,26] and childhood overweight or obesity . LGA infants, in particular, are at risk for multiple adverse short- and long-term sequelae. (See "Large for gestational age newborn", section on 'Neonatal morbidity' and "Large for gestational age newborn", section on 'Potential long-term effects'.)
For the mother, it can result in postpartum weight retention. Women experience modest increases in body weight and fat distribution after a first pregnancy; these changes may be persistent and vary according to race and ethnic background . Excessive gestational weight gain can lead to significant postpartum weight retention and eventual obesity, which has multiple adverse health consequences (see "Overweight and obesity in adults: Health consequences"). In its 2009 report, the IOM stated that an analysis restricted to data collected at ≥24 weeks postpartum found that more than 60 percent of women in all racial/ethnic groups who gained above the range recommended by IOM 1990 retained >10 lb (4.5 kg) postpartum and more than 40 percent of women who gained excessively retained >20 lb (9.1 kg) .
Excessive gestational weight gain in a first pregnancy is predictive of excessive weight gain in subsequent pregnancies . Adding to this problem, women are more likely to gain rather than lose weight between pregnancies, and weight gain from one pregnancy to the next increases the risks of gestational diabetes mellitus, pregnancy-induced hypertensive diseases, cesarean delivery, preterm birth, LGA, stillbirth, and cleft palate .
Avoiding excessive gestational weight gain and postpartum weight retention are important and potentially modifiable targets to achieve lower risks of adverse outcomes in subsequent pregnancies and prevent future maternal obesity and its adverse consequences. A meta-analysis of postpartum interventions for weight loss demonstrated that a combined dietary and physical activity intervention produced greater postpartum weight loss compared with no intervention (mean difference -2.49 kg, 95% CI -3.34 to -1.63 kg, 12 studies, 1156 women), and the weight loss was maintained at 12 months postpartum in four studies . Although traditional behavioral interventions for achieving and maintaining weight loss have had limited success, some promising new approaches have been investigated. For example, a randomized trial found that an internet-based lifestyle intervention resulted in greater postpartum weight loss than usual care . (See "Obesity in adults: Overview of management".)
Weight gain below IOM target range
Pregnancy outcomes — The major concern of gestational weight gain below the IOM target range is an adverse effect on birth weight and increased risks for SGA and preterm birth [16,21], but not stillbirth . Since birth weight is related to both maternal body mass index (BMI) and gestational weight gain, the risk of these adverse outcomes is higher in women who are underweight by BMI and do not achieve the IOM target range than in women with normal, overweight, or obese BMI who do not achieve the IOM target range.
In the 2017 systematic review described above that evaluated pregnancy outcomes of women with gestational weight gain above or below 2009 IOM guidelines, compared with women with gestational weight gain within the recommended range, low gestational weight gain was associated with :
●Higher risk of preterm birth (OR 1.70, 95% CI 1.32-2.20; ARD 5 percent, 95% CI 3-8). However, weight gain was not adjusted for gestational age, potentially resulting in less total gestational weight gain than would have been otherwise attained. Spontaneous and induced preterm birth were not clearly differentiated.
●Higher risk of SGA (OR 1.53, 95% CI 1.44-1.64; ARD 5 percent, 95% CI 4-6).
●Lower risk of LGA (OR 0.59, 95% CI 0.55-0.64; ARD -2 percent, 95% CI -10 to -6).
●Lower risk of macrosomia (OR 0.60, 95% CI 0.52-0.68; ARD -2 percent, 95% CI -3 to -1).
●No difference in cesarean delivery (OR 0.98, 95% CI 0.96-1.02; ARD 0 percent, 95% CI -2 to 1).
Although observational studies have reported a variety of other adverse outcomes in offspring of women with poor gestational weight gain, these reports are prone to bias and confounding.
Postpartum outcomes — Inadequate gestational weight gain may lower the risk of postpartum weight retention. In a meta-analysis, women with an inadequate gestational weight gain had substantially lower mean postpartum weight retention (mean -2.14 kg, 95% CI -2.61 to -1.66) than women with an adequate gestational weight gain (mean 3.15 kg, 95% CI 2.47-3.82) up to 21 years postpartum .
Although postpartum weight retention is undesirable, the increased risk and long-term morbidity of SGA related to inadequate weight gain should be the dominant consideration; postpartum weight can be lost through diet and exercise.
PRECONCEPTION COUNSELING — Health care providers should determine a woman's body mass index (BMI) during office visits for preconception counseling (calculator 1) . This information is used to guide recommendations regarding nutrition, physical activity, and weight gain/loss before, during, and after pregnancy.
●Underweight women – Approximately 4 to 5 percent of United States women are underweight before conception . These women should be encouraged to reach a normal BMI before pregnancy. Referral to a nutritionist might be helpful. The presence of an eating disorder should be considered. (See "Eating disorders in pregnancy".)
●Overweight and obese women – The prevalence of overweight or obese individuals is high in the United States: In various reports, 30 to 50 percent of women had BMIs in the overweight or obese range [35-37]. Weight reduction before pregnancy can improve pregnancy outcome. (See "Obesity in pregnancy: Complications and maternal management", section on 'Prepregnancy weight loss'.)
Preconception counseling should include information on the risks of obesity for the mother, pregnancy, and child (see "Obesity in pregnancy: Complications and maternal management"); encouragement for weight reduction, which may include information about diet, exercise, weight loss programs, and the favorable effects on pregnancy outcome; and referral to a weight reduction specialist for discussion of options such as behavior modification, pharmacotherapy, or bariatric surgery, if appropriate. (See "Obesity in adults: Overview of management".)
There is minimal literature on the safety of dietary restrictions for intentional weight loss during the periconceptional period. Any influences on early embryonic development and the later health of the child are largely unknown. In counseling patients who were dieting at the time of conception, we review the reassuring outcome data from studies of women with nausea and vomiting of pregnancy who lost weight early in pregnancy but had subsequent normal weight gain. (See "Nausea and vomiting of pregnancy: Treatment and outcome", section on 'Outcome and prognosis'.)
The safety of drug therapy for weight loss during pregnancy has not been demonstrated. Drugs intended for weight loss should be avoided. Specific issues related to metformin are reviewed below. (See 'Metformin' below.)
CARE AND COUNSELING FOR PREGNANT WOMEN
Overview — As pregnant women are particularly concerned about their health and the health of their child and in frequent contact with their health care providers, pregnancy is an ideal time for promotion of weight control and adoption of a healthy lifestyle . Antenatal dietary and physical activity-based lifestyle interventions are associated with reduced gestational weight gain . Importantly, reduced gestational weight gain lowers the risk for adverse maternal and newborn outcomes [39-41].
●A United States Preventive Services Task Force (USPSTF) systematic review of 68 studies found adequate evidence that behavioral counseling (nutrition, physical activity, lifestyle and behavioral change) and/or activity-related interventions that limit excess gestational weight gain result in a 10 to 20 percent reduction in some adverse pregnancy outcomes (eg, gestational diabetes, emergency cesarean birth, macrosomia, large for gestational age) when trials recruiting normal weight, overweight, obese, and weight heterogeneous women were combined [40,41].
Of note, almost all participants in the trials were overweight or obese, and there was no evidence of improved clinical outcomes amongst trials recruiting women with obesity only. The mean reduction in gestational weight gain was about 1 kg in the trials, suggesting that even a modest reduction in weight gain can result in modest improvement in pregnancy outcomes.
The analysis was not able to determine the specific components of the behavioral interventions that were effective, such as number, frequency, and duration of sessions or the type of session, but higher-intensity intervention (at least 12 sessions) was more successful than lower intensity and had no demonstrable harm.
We agree with the USPSTF recommendation that clinicians should offer pregnant persons effective behavioral counseling interventions aimed at promoting healthy weight gain and preventing excessive gestational weight gain in pregnancy. Challenges include the lack of information about the most effective interventions and how best to implement them.
In the United States, women are advised to self-monitor weight throughout pregnancy, and clinicians routinely monitor weight at prenatal visits so that inadequate or excessive gestational weight gain can be identified early and corrective interventions can be taken . In contrast to this practice, some guideline (eg, United Kingdom ) do not recommend routine weighing of pregnant women, unless they are considered to be at risk of adverse outcomes, clinical management will be impacted, or nutrition is a concern.
However, a minority of women achieve recommended targets (table 3). Population-based data from the Pregnancy Risk Assessment Monitoring System (PRAMS) showed that the percent of American women who met, exceeded, and did not achieve Institute of Medicine (IOM) weight gain target ranges was 32, 47, and 21 percent, respectively . Compared with women of normal weight, overweight and obese women were more likely to have excessive gestational weight gain and underweight women were more likely to have inadequate gestational weight gain.
Lack of appropriate counseling may account, in part, for these findings. In a survey of Canadian women, only a minority reported being counseled correctly about how much weight to gain during pregnancy or the risks of inappropriate weight gain . Similarly, a survey of obstetric providers in Massachusetts noted 37 percent did not know the minimum body mass index (BMI) for diagnosing obesity, and most advised gestational weight gains that were discordant with IOM guidelines in effect at that time .
Epidemiologic factors also play a role. In longitudinal studies, African American women had as much as threefold higher median gestational weight gain than White women, even if prepregnancy BMI was normal [47-50]. By contrast, Hispanic women were more likely to have inadequate gestational weight gain when compared with their non-Hispanic counterparts .
Underweight women — Underweight women should be encouraged to meet IOM recommendations for gestational weight gain to lower their risk of having a small for gestational age (SGA) infant [52-54].
Approach to weight gain below IOM recommendations — If weight gain between prenatal visits is inadequate (less than 0.5 lb [0.23 kg] per week), clinicians are advised to evaluate the woman's eating habits and other potential etiologies of deficient weight gain and to assess whether fetal growth is likely to be impacted.
Insufficient weight gain may be due to a number factors, including but not limited to smoking, nausea and vomiting of pregnancy/hyperemesis gravidarum, medical disease, eating disorder, or food insecurity.
Management depends on the etiology. Interventions that may be useful in women with inadequate weight gain include optimizing the status of related underlying medical or psychiatric disorders, frequent contact with nurses or nutrition specialists, suggestions for changes in diet and physical activity, and, for some women, improved access to healthy foods.
Approach to weight gain above IOM recommendations — Since birth weight is related to both maternal BMI and gestational weight gain, women with low prepregnancy BMI can benefit from gestational weight gain above the IOM target range. Their baseline risk of SGA births is relatively high, so achieving a higher birth weight from higher gestational weight gain will reduce their frequency of SGA births and improve neonatal outcomes.
It should be noted that this is not the case for women with prepregnancy BMI in the normal, overweight, or obese category: In these women, the baseline risk of SGA is not high, so achieving a higher birth weight from higher gestational weight gain does not substantially reduce the frequency of SGA, but does increase rates of large for gestational age (LGA) and macrosomia, and, in turn, increases suboptimal neonatal outcomes [55-57]. For these women, any birth weight benefits associated with a higher mean birth weight are offset by the increased maternal and pediatric consequences of delivering an LGA or macrosomic newborn. (See "Fetal macrosomia", section on 'Significance' and "Large for gestational age newborn".)
Overweight and obese women — Overweight and obese women should be encouraged to meet IOM recommendations for gestational weight gain to reduce maternal and pediatric hazards of excessive gestational weight gain (see 'Weight gain above IOM target range' above). The percentage of pregnant women who gained >18 kg (40 lb) by term was almost 22 percent in one report , and most of these women were likely overweight or obese at baseline: 60 percent of overweight women have excessive gestational weight gain by IOM standards (>11 kg [25 lb]) versus 40 percent of normal weight women (>16 kg [35 lb]) .
Approach to weight gain above IOM recommendations — If weight gain between prenatal visits is excessive (more than 1.5 lb [0.68 kg] per week), clinicians are advised to evaluate the woman's eating habits and other potential etiologies of excessive weight gain. In the absence of pathologic edema (eg, preeclampsia, heart failure, nephropathy), excessive gestational weight gain is primarily related to an excessive increase in maternal adiposity, generally the result of positive maternal energy balance (ie, calorie intake above the metabolic needs of pregnancy, which are an additional 200 to 300 calories/day). For some women, substantially reduced energy expenditure may also play a role.
Data from randomized trials on lifestyle/behavioral interventions for avoiding excessive gestational weight gain do not conclusively support the efficacy of any approach for improving relevant pregnancy outcomes [60-62], although an individual patient data meta-analysis found a modest reduction in the rate of cesarean delivery (odds ratio [OR] 0.91, 95% CI 0.83-0.99) . When study level data from studies that did not provide individual patient data were included, a reduction in gestational diabetes was also observed (OR 0.76, 95% CI 0.65-0.89). The actual difference in gestational weight gain between the intervention and control groups was small (mean difference -0.70 kg, 95% CI -0.92 to -0.48).
Diet and exercise — As in nonpregnant individuals, exercise (if there are no contraindications) with or without a healthy diet helps to prevent excessive weight gain . (See "Obesity in adults: Overview of management" and "Exercise during pregnancy and the postpartum period".)
Several systematic reviews and meta-analyses have examined the effect of standard antenatal behavioral interventions (eg, counseling about diet, physical activity, optimum weight gain; goal setting) for prevention of excessive weight gain during pregnancy [60,64-70]. Although some of these analyses found that these interventions significantly decreased gestational weight gain compared with usual care, there was no clear clinically significant reduction in maternal complications or adverse neonatal outcomes. Published intervention trials have generally been of small size and insufficient quality to allow evidence-based recommendations to be developed for clinical practice .
Large well-designed randomized trials have illustrated the challenges of limiting gestational weight gain at the population level. For example:
●In the LIMIT trial, over 2000 pregnant women with BMI ≥25 kg/m2 were randomly assigned to usual care or a comprehensive intervention that included a combination of healthy dietary, exercise, and behavioral strategies provided by a research dietician and trained research assistants . Gestational weight gain and almost all pregnancy outcomes (eg, preterm birth, LGA infant, preeclampsia, gestational diabetes) were similar for both groups; however, the intervention group had fewer births >4000 g (15 versus 19 percent; relative risk 0.82, 95% CI 0.68-0.99).
●The United Kingdom Pregnancies Better Eating and Activity Trial randomized over 1500 obese pregnant women to usual care or to eight weekly sessions with a health trainer who provided support and advice about a low glycemic index diet and increased physical activity, as well as strategies for overcoming barriers to behavioral change . Although the intervention group had less gestational weight gain (7.19 versus 7.76 kg) and reduced measures of adiposity, the primary outcomes of gestational diabetes mellitus and LGA infants did not differ between groups.
Metformin — In studies involving women with gestational diabetes mellitus, metformin reduced gestational weight gain in addition to its antihyperglycemic effects [72,73]. However, in women without diabetes, based on a meta-analysis of two trials from the UK described below [74,75] and a third trial (PACTR201505001142202) from Egypt , metformin did not clearly reduce gestational weight gain compared with placebo (mean difference 2.60 kg lower, 95% CI 5.29 lower to 0.10 higher) .
In both the Metformin in Obese Nondiabetic Pregnant Women (MOP) trial and the Effect of Metformin on Maternal and Fetal Outcomes in Obese Pregnant Women (EMPOWaR) trial, metformin did not affect the primary outcome (birth weight, LGA) compared with placebo [74,75]. In MOP, but not EMPOWaR, metformin reduced gestational weight gain (4.6 versus 6.3 kg) and the rate of preeclampsia (3.0 versus 11.3 percent). In PACTR201505001142202, metformin also reduced mean gestational weight gain compared with placebo (6.5 versus 11.6 kg) but did not reduce the incidence of hypertension .
Approach to weight gain below IOM recommendations — We advise overweight/obese women with gestational weight gain below that recommended by the IOM not to try to increase weight gain if the fetus is growing appropriately on ultrasound examination, as such women do not appear to be at increased risk of adverse outcome and some risks appear to be reduced. Our approach is supported by several studies in which overweight/obese women who gained only 6 to 14 lb (2.7 to 6.4 kg) had similar or better neonatal outcomes as overweight/obese women whose weight gain was higher and within IOM recommendations of 15 to 25 lb (7.0 to 11.5 kg) [13,78-85].
The optimum amount of weight gain for overweight/obese women is controversial. Maternal obesity is protective against low birth weight and the tendency towards higher birth weight percentiles persists, even in the presence of factors that might be expected to lower birth weight (eg, low maternal weight gain, hypertension) . Weight gain below IOM guidelines appears to reduce the risk of macrosomia, pregnancy-related hypertension, and obstetric interventions . However, fetal growth appears to be reduced in overweight/obese women with insufficient gestational weight gain.
In a prospective study of singleton term pregnancies that compared newborn anthropometry for 1053 overweight and obese women who gained >5 kg with that of 188 overweight and obese women who either lost weight or gained ≤5 kg, women who gained ≤5 kg had significantly more SGA newborns (9.6 versus 4.9 percent) and their neonates had statistically lower birth weight (3258 versus 3467 g), lean body mass (2855 versus 2995 g), fat mass (403 versus 471 g), percent fat mass (12 versus 13.2 percent), head circumference (34.2 versus 34.5 cm), and length (49.3 versus 50.0 cm) . There was no difference in gestational age at delivery (38.8 versus 38.9 weeks). The clinical significance of these small but statistical differences in newborn morphometry is unknown; long-term follow-up studies are needed.
Approach to weight loss — Available data from observational studies suggest weight loss in obese women decreases some pregnancy complications associated with obesity (LGA, pregnancy-related hypertension ) but also reduces birth weight  and may increase the risk of preterm delivery in overweight women and women with class I obesity . No randomized trials have been performed .
In a 2015 meta-analysis of six cohort studies of pregnancy outcomes among obese women with gestational weight loss, weight loss increased the risk of having an SGA infant by approximately 75 percent and decreased the risk of LGA by approximately 40 percent compared with obese women with appropriate gestational weight gain :
●SGA <10th percentile (adjusted OR [aOR] 1.76, 95% CI 1.45-2.14) and SGA <3rd percentile (aOR 1.62, 95% CI 1.19-2.20)
●LGA >90th percentile (aOR 0.57, 95% CI 0.52-0.62)
●Cesarean delivery (aOR 0.73, 95% CI 0.67-0.80)
None of the studies in the analysis assessed the effect of weight loss on preterm birth rates or long-term outcomes in offspring.
A limitation of the meta-analysis is that the amount of weight loss was not considered. A small (<5 kg) weight loss in class II and III obese women (BMI 35.0 to 39.9 and BMI ≥40, respectively) may have more benefits than risks and may not increase the risk of having an SGA infant [88,89].
Women with multiple gestations — Gestational weight gain in women with multiple gestations is discussed separately. Data-based guidelines are available for twin pregnancies but not for triplets and higher order gestations.
●Twin pregnancies – (See "Twin pregnancy: Routine prenatal care", section on 'Gestational weight gain' and "Twin pregnancy: Overview".)
●Triplet pregnancies – (See "Triplet pregnancy", section on 'Weight gain'.)
Women who have had bariatric surgery — Information on women who have had bariatric surgery can be found separately. (See "Fertility and pregnancy after bariatric surgery", section on 'Gestational weight gain'.)
Women with eating disorders — Information on women who have an eating disorder can be found separately. (See "Eating disorders in pregnancy".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Pregnancy in women with obesity".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Prenatal care (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Physiologic changes related to pregnancy result in a weight gain of approximately 25 lb (11 kg). (See 'Physiologic weight gain' above.)
●Clinicians should offer pregnant persons effective behavioral counseling interventions aimed at promoting healthy weight gain and preventing excessive gestational weight gain in pregnancy. (See 'Overview' above.)
●The Institute of Medicine (IOM, now National Academies of Sciences, Engineering, and Medicine) has made recommendations for weight gain during pregnancy, stratified by maternal prepregnancy body mass index (BMI) (table 3). (See 'Recommendations for gestational weight gain' above.)
●Gestational weight gain above the IOM target range in the overall obstetric population has been associated with an increased risk of macrosomic and large for gestational age infants, cesarean delivery, pregnancy-related hypertension (gestational hypertension, preeclampsia), and gestational diabetes. (See 'Weight gain above IOM target range' above.)
Gestational weight gain below the IOM target range in the overall obstetric population has been associated with lower birth weight and an increased risk for small for gestational age (SGA) infants. Since birth weight is related to both maternal BMI and gestational weight gain, this risk is more significant in women who are underweight by BMI and do not achieve the IOM target range than in women with normal, overweight, or obese BMI who do not achieve the IOM target range. (See 'Weight gain below IOM target range' above.)
●Prepregnancy BMI appears to be a more important predictor of pregnancy outcome than gestational weight gain, suggesting that prepregnancy BMI is a more important target for intervention. (See 'Subsequent data that may inform guidance for gestational weight gain' above.)
●Underweight women should be encouraged to reach a normal BMI before pregnancy and to meet IOM recommendations for gestational weight gain to lower their risk of having an SGA infant. (See 'Underweight women' above and 'Preconception counseling' above.)
●If weight gain between prenatal visits is inadequate (less than 0.5 lb [0.23 kg] per week), the woman's eating habits and other potential etiologies of weight gain outside of the recommended range should be evaluated. Insufficient weight gain may be due to a number factors, including but not limited to smoking, nausea and vomiting of pregnancy/hyperemesis gravidarum, medical disease, eating disorder, or food insecurity. Management depends on the etiology. Interventions that may be useful in women with inadequate weight gain include optimizing the status of related underlying medical disorders, frequent contact with nurses or nutrition specialists, suggestions for changes in diet and physical activity, and for some women, improved access to healthy foods. (See 'Approach to weight gain below IOM recommendations' above.)
●Since birth weight is related to both maternal BMI and gestational weight gain, underweight women can benefit from gestational weight gain above the IOM target range because it will reduce their risk of an SGA birth. (See 'Approach to weight gain above IOM recommendations' above.)
●Overweight/obese women should be encouraged to reach a normal BMI before pregnancy and to meet IOM recommendations for gestational weight gain. Prepregnancy and postpartum counseling of overweight/obese women should include information on the risks of obesity for the mother, pregnancy, and child and encouragement for weight reduction, which may include information about diet/dietary goals, exercise, and weight loss programs, and referral to a weight-reduction specialist for discussion of options such as behavior modification, pharmacotherapy, or bariatric surgery, if appropriate. (See 'Preconception counseling' above.)
●Women who are obese may not require an increase in energy intake in the second and third trimesters to meet the metabolic demands of pregnancy. If gestational weight gain is below IOM recommendations, we do not encourage the woman to increase the rate of weight gain if the fetus is growing appropriately as overweight/obese women who gain below IOM recommendations, or even gain no weight or lose some weight (5 to 10 pounds, for obese women only), do not appear to be at increased risk of adverse neonatal outcome and some risks appear to be reduced (macrosomia, pregnancy-related hypertension, obstetric interventions). (See 'Approach to weight gain below IOM recommendations' above and 'Novel research on caloric intake' above.)
●If weight gain between prenatal visits is excessive (more than one and a half lb [0.68 kg]) per week, the woman's eating habits and other potential etiologies of excessive weight gain should be evaluated. In the absence of pathologic edema (eg, preeclampsia, heart failure, nephropathy), excessive gestational weight gain is primarily related to an excessive increase in maternal adiposity, generally the result of positive maternal energy balance. Data from randomized trials on lifestyle/behavioral interventions for avoiding excessive gestational weight gain do not conclusively support the efficacy of any approach for improving relevant pregnancy outcomes. (See 'Approach to weight gain above IOM recommendations' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges George Macones, MD, MSCE, who contributed to an earlier version of this topic review.