Gestational weight gain

INTRODUCTION — 

Gestational weight gain (GWG) 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 and may be more accurate in patients who initiate prenatal care after the first trimester [1]. The ending weight is often considered the weight recorded at the last prenatal office visit, which is typically within a few days of a term birth but may be two to four weeks before a preterm birth.

Both maternal prepregnancy body mass index (BMI) and GWG influence maternal, obstetric, and pediatric outcomes. Although the importance of both optimal prepregnancy BMI and GWG are well established, many individuals begin pregnancy with a BMI above the healthy range (ie, above the normal weight for height) and many gain too much weight during pregnancy [2-4]. Some individuals begin pregnancy with a BMI below the healthy range and/or have inadequate GWG; this can also have adverse effects on pregnancy, most importantly preterm birth and a small for gestational age (SGA) infant.

This topic will discuss issues relating to GWG, focusing on guidelines by the Institute of Medicine (IOM, now the National Academies of Sciences, Engineering, and Medicine [NAM]). Other guidelines regarding GWG are available worldwide [5,6]. Detailed discussions of obstetric issues in pregnant people with obesity or an eating disorder can be found separately. (See "Obesity in pregnancy: Complications and maternal management" and "Eating disorders in pregnancy".)

PHYSIOLOGIC WEIGHT GAIN IN TERM SINGLETON PREGNANCIES — 

For individuals who conceive with a BMI in the healthy range (18.5 to 24.9 kg/m²) and gain the National Academy of Medicine (NAM)'s recommended 25 to 35 lbs (11.5 to 16 kg), most weight gain is physiologic and distributed at term 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)

GUIDANCE

Development — In 1990, the Committee on Nutritional Status During Pregnancy and Lactation of the Institute of Medicine (IOM, which became National Academies of Sciences, Engineering, and Medicine [NAM] in 2015) formulated recommendations for healthy GWG after performing a detailed analysis of all published data pertaining to prepregnancy weight, weight gain during pregnancy, and pregnancy outcome [7]. The goal was to increase the likelihood of a favorable pregnancy outcome, which was defined as birth of a term live-born infant with birth weight between 3000 and 4000 grams.

In 2009, the 1990 recommendations were revised based on findings from research performed over almost two decades following their initial publication. The updated recommendations included GWG recommendations for twin pregnancies, changes to the recommendations for pregnant people with obesity, and a recommendation that all females strive to be within the healthy BMI range when they conceive [8]. The World Health Organization (WHO) criteria for defining BMI categories were adopted in the revision, as well.

The 2009 recommendations were still based on observational data, and focused on some but not all relevant clinical outcomes. While robust data were available for the relationship between GWG and rates of outcomes such as small for gestational age (SGA) and large for gestational age (LGA) births, cesarean birth, and postpartum weight retention, data regarding relationships with other important clinical outcomes such as rates of gestational diabetes, preeclampsia, and preterm birth and data for the different classes of obesity were not considered adequately robust to be included.

Specific recommendations for singleton and twin pregnancies — The following GWG recommendations are for the general obstetric population in the United States. They are based on four prepregnancy BMI categories and singleton or twin gestation, and are independent of age, parity, smoking history, race, and ancestry because the authors felt that the relationship between GWG and pregnancy outcome had not been evaluated adequately to enable evidence-based recommendation based on these and other factors (eg, extremes of maternal age, extremes of BMI below or above the underweight and obese thresholds, triplets and higher order multiple gestations).

●Singleton pregnancy

•BMI <18.5 kg/m² (underweight) – 28 to 40 lb (12.5 to 18.0 kg)

•BMI 18.5 to 24.9 kg/m² (normal weight) – 25 to 35 lb (11.5 to 16.0 kg)

•BMI 25.0 to 29.9 kg/m² (overweight) – 15 to 25 lb (7.0 to 11.5 kg)

•BMI ≥30.0 kg/m² (obese) – 11 to 20 lb (5 to 9.0 kg)

●Twin pregnancy

•BMI <18.5 kg/m² (underweight) – No recommendation due to insufficient data

•BMI 18.5 to 24.9 kg/m² (normal weight) – 37 to 54 lb (16.8 to 24.5 kg)

•BMI 25.0 to 29.9 kg/m² (overweight) – 31 to 50 lb (14.1 to 22.7 kg)

•BMI ≥30.0 kg/m² (obese) – 25 to 42 lb (11.4 to 19.1 kg)

The recommendations for twin pregnancies were considered provisional because of lack of data about the consequences of GWG on longer-term health outcomes. The targets can be reached by a modest increase in energy intake in the second and third trimesters; however, patients with obesity may not require this increase to meet the metabolic demands of pregnancy. (See 'Pregnant people with obesity and weight loss' below.)

Validation data

●In a 2017 systematic review that evaluated pregnancy outcome with respect to IOM/NAM recommendations (23 cohort studies, 1.3 million participants): 47 percent of participants exceeded the upper limit of IOM/NAM-recommended GWG and 23 percent did not achieve the lower limit of recommended GWG [9].

Compared with individuals with GWG within the recommended range, excessive GWG 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). However, this outcome should be interpreted cautiously because weight gain was not adjusted for gestational age, potentially resulting in less total GWG than would have been otherwise attained. In addition, spontaneous and induced preterm birth were not clearly differentiated.

•Lower risk of 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 birth (OR 1.30, 95% CI 1.25-1.35; ARD 4 percent, 95% CI 3-6).

Low GWG was associated with:

•Higher risk of preterm birth (OR 1.70, 95% CI 1.32-2.20; ARD 5 percent, 95% CI 3-8). As noted above, weight gain was not adjusted for gestational age, potentially resulting in less total GWG 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 birth (OR 0.98, 95% CI 0.96-1.02; ARD 0 percent, 95% CI -2 to 1).

There were several limitations of the systematic review, notably inclusion of few studies from resource-limited countries; inconsistent definitions of preterm birth, cesarean birth, and macrosomia; inclusion of studies published before the IOM/NAM 2009 recommendations (thus, with somewhat different GWG target ranges); and inability to evaluate gestational diabetes mellitus (GDM) as an outcome. In addition, observational studies are prone to bias and confounding.

Excessive GWG above IOM/NAM targets has also been shown to have long-term effects on the mother and offspring. For offspring, neonatal adiposity [10,11] and childhood overweight or obesity [12] are increased. LGA neonates in particular are at risk for multiple adverse short- and long-term sequelae. (See "Large for gestational age (LGA) newborn", section on 'Complications' and "Large for gestational age (LGA) newborn", section on 'Potential long-term effects'.)

For the mother, excessive GWG 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/NAM stated that an analysis restricted to data collected at ≥24 weeks postpartum found that more than 60 percent of pregnant people in all racial/ancestry groups who gained above the range recommended by IOM/NAM 1990 retained >10 lb (4.5 kg) postpartum and more than 40 percent of those who gained excessively retained >20 lb (9.1 kg) [8]. In a study including nearly 28,000 individuals with prepregnancy BMI in the normal range, GWG above the 2009 IOM/NAM recommendations was associated with increased all-cause mortality (adjusted hazard ratio [aHR] 1.09, 95% CI 1.01-1.18) and cardiovascular mortality (aHR 1.20, 95% CI 1.04-1.37) at median follow-up of 52 years, after adjustment for multiple index pregnancy covariates [13]. Individuals with prepregnancy BMIs in the overweight range also had a significant increase in all-cause mortality (aHR 1.12, 95% CI 1.01-1.24). These findings support previous evidence that GWG above 2009 IOM/NAM recommendations contributes to the accumulation of visceral adiposity and suggests that this, in turn, increases the risk of chronic diseases and subsequent mortality. Furthermore, excessive GWG in a first pregnancy is predictive of excessive GWG in subsequent pregnancies [14]. Adding to this problem, individuals are more likely to gain rather than lose weight between pregnancies, and weight gain from one pregnancy to the next appears to increase the risks of GDM, pregnancy-induced hypertensive diseases, cesarean birth, preterm birth, LGA, stillbirth, and cleft palate [15], although studies are inconsistent for some of these outcomes [16].

The major concern of GWG below the IOM/NAM target range is an adverse effect on birth weight and increased risks for SGA and preterm birth [9,17], but not stillbirth [18]. Since birth weight is related to both maternal BMI and GWG, the risk of these adverse outcomes is higher in pregnant people who are underweight by BMI and do not achieve the IOM/NAM target range than in those with normal, overweight, or obese BMI who do not achieve the IOM/NAM target range. In fact, there is increasing evidence that GWG recommendations should be revised downward for individuals with obesity, particularly those with class III obesity (see 'Pregnant people with obesity and weight loss' below). Furthermore, inadequate GWG appears to lower the risk of postpartum weight retention. In a meta-analysis, pregnant people with an inadequate GWG had substantially lower mean postpartum weight retention (mean -2.14 kg, 95% CI -2.61 to -1.66) than those with an adequate GWG (mean 3.15 kg, 95% CI 2.47-3.82) up to 21 years postpartum [19]. Although postpartum weight retention is undesirable, the dominant consideration for patients with BMI in the underweight or normal range should be the increased risk and long-term morbidity of SGA related to inadequate GWG.

Subsequent data that may inform usual guidance

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 GWG and more clinical outcomes than assessed by the IOM/NAM [20]. These outcomes included preeclampsia, pregnancy-induced hypertension, GDM, cesarean birth, preterm birth, SGA, and LGA. Their GWG recommendations (table 1) were developed based on the association of GWG with these adverse outcomes.

The LifeCycle Study Group provided separate recommendations for the three classes of obesity. Pregnant people with class III obesity had a greater overall risk for any adverse outcome than those with class II obesity, and those with class II obesity had a greater overall risk for any adverse outcome than those with class I obesity for almost all GWGs (eg, for weight gain ≥16 kg, the overall risks for any adverse outcome for pregnant people with class III, II, and I obesity were 79, 64, and 43 to 56 percent, respectively). Although GWG ranges associated with optimal outcomes for each class of obesity were developed, the predictive power of GWG for the different adverse pregnancy outcomes in any category of prepregnancy BMI was either low or moderate, thus challenging the clinical usefulness of the IOM/NAM GWG ranges. Since the absolute risk for any adverse outcome increased across the prepregnancy BMI range and was largely independent of GWG, a reasonable conclusion is that prepregnancy BMI, particularly prepregnancy obesity, is a more important target for interventions than GWG.

As in other studies, pregnant individuals in the prepregnancy normal, overweight, and obesity class I and II categories with excessive GWG had increased odds of preeclampsia and pregnancy-induced hypertension. Paradoxically, however, normal and overweight individuals with inadequate GWG had increased odds of GDM and individuals with obesity classes I and II with excessive GWG had reduced odds.

Other data

●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 GWG (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" [21]. As in other large studies, pregnant people in the healthy BMI class had the lowest rates of infant morbidity and mortality (8 and 0.28 percent, respectively) and those with class III obesity had the highest rates of these outcomes (12.4 and 0.58 percent, respectively).

The authors proposed the following GWG ranges as optimal for reducing the risks of serious infant morbidity and mortality:

•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)

GWG less than these proposed lower boundaries (including weight loss) had a greater impact on infant mortality among individuals who were underweight or had a normal BMI compared with individuals with obesity, but the latter also experienced increased rates of infant mortality when GWG was less than the lower boundary.

By comparison, IOM/NAM 2009 recommendations were not stratified by class I, II, and III obesity, the lower GWG boundary for all three classes was lower (11 lb [5 kg]), and was targeted to optimizing pregnancy outcomes such as low birth weight rather than "serious infant morbidity and mortality." The relationship between the lower boundary of GWG and increased infant morbidity and mortality in this study may be a marker of pathologic maternal factors, rather than causal.

●Traditional guidelines for energy intake, as applied to pregnant people with obesity, have been challenged by a detailed investigation of the relationship between energy intake, energy expenditure, energy balance, and GWG in 54 pregnant people with obesity [22]. Estimates of energy intake from self-reported food frequency questionnaires are often confounded by underreporting. Therefore, energy intake over the second and third trimesters was directly determined by the energy intake-balance method in this study. This 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 participants demonstrated excessive GWG by IOM/NAM recommendations for pregnant people with BMI ≥30 kg/m²; eight achieved GWG within the recommended range, and 10 did not achieve the recommended GWG. In pregnant people who achieved GWG within the recommended range, energy intake was less than energy expenditure. By contrast, for those with excessive GWG, energy intake exceeded expenditure by 186±29 kcal/day and this was associated with an increase in maternal adiposity, not an increase in 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 people with obesity. Rather, they suggested that the energy requirements are met by mobilization of fat stores.

These interesting observations should not be applied to clinical practice until appropriately powered studies evaluate the effects of active intake reduction on clinical outcomes. Accurate measurement of energy balance cannot be achieved in a large study and proxy measures may be inaccurate, potentially confounding further study.

PREPREGNANCY COUNSELING AND CARE — 

Health care providers should determine a patient's BMI during office visits for prepregnancy counseling (calculator 1) [23]. This information is used to guide recommendations regarding nutrition, physical activity, and weight gain/loss before, during, and after pregnancy. Prepregnancy BMI appears to be a more important predictor of pregnancy outcome than GWG, suggesting that prepregnancy BMI is the most important target for intervention. (See 'LifeCycle Project weight gain recommendations' above.)

●Individuals who are underweight – Approximately 4 to 5 percent of females in the United States are underweight before conceiving [24]. These individuals should be encouraged to reach a healthy BMI before pregnancy, which has long-term benefits regardless of pregnancy status. Referral to a nutritionist might be helpful. The possibility of an eating disorder should be considered and treated if present. (See "Eating disorders in pregnancy".)

●Individuals who are overweight or obese – In various reports, 30 to 50 percent of females in the United States had BMIs in the overweight and obesity ranges [24-26].

Prepregnancy counseling should include information on the risks of obesity for the mother, pregnancy, and child and encourage weight reduction. Weight reduction before pregnancy can improve pregnancy outcome and has long-term health benefits (see "Obesity in pregnancy: Complications and maternal management" and "Obesity in adults: Overview of management", section on 'Importance of weight loss'). Referral to a weight reduction specialist for discussion of options (eg, behavior modification; pharmacotherapy; or bariatric surgery, if appropriate) can be helpful. (See "Obesity in adults: Overview of management".)

Two important issues are restrictive diets and pharmacotherapy for intentional weight loss. Some popular restrictive diets (eg, very low-carbohydrate diets) are potentially harmful during pregnancy (see "Nutrition in pregnancy: Assessment and counseling", section on 'Issues regarding self-imposed dietary restraints'). Most medications intended for weight loss are also potentially harmful during pregnancy. In particular, some of the popular once-weekly subcutaneous GLP-1 agonists (eg, semaglutide) have long half-lives and ideally should be stopped at least two months prior to conception because of the teratogenic effects seen in animals. (See "Obesity in adults: Drug therapy" and "Preexisting (pregestational) diabetes: Preconception counseling, evaluation, and management", section on 'Patients on preconception noninsulin antihyperglycemic agents'.)

In studies involving patients with gestational diabetes mellitus (GDM), metformin reduced GWG in addition to its antihyperglycemic effects [27,28]. However, in pregnant people without diabetes, metformin did not clearly reduce GWG compared with placebo (mean difference 2.60 kg lower, 95% CI 5.29 lower to 0.10 higher) in a meta-analysis of three trials [29]. Further study is indicated given the lack of consistency among the trials.

PRENATAL COUNSELING AND CARE

Routine care

Monitoring GWG — In the United States, clinicians routinely monitor GWG at prenatal visits [30], whereas in the United Kingdom guidance from the National Institute for Health and Care Excellence (NICE) does not advise routinely weighing pregnant people, unless they are considered to be at risk of adverse outcomes, clinical management will be impacted, or nutrition is a concern [31].

Only a minority of pregnant people in the United States achieve recommended IOM/NAM 2009 targets (table 2). Population-based data from the Pregnancy Risk Assessment Monitoring System (PRAMS) showed that the percent of pregnant people in the United States who exceeded, met, and did not achieve IOM/NAM weight gain target ranges was 47, 32, and 21 percent, respectively [32]. Compared with pregnant people with BMI in the normal range, those who were overweight or obese were more likely to have excessive GWG and those who were underweight were more likely to have inadequate GWG.

Although IOM/NAM recommendations for total GWG have been validated (see 'Validation data' above), the optimal weekly weight gain across pregnancy to achieve the GWG target is a clinical judgment as it has not been studied extensively nor validated.

Behavioral counseling — Clinicians should offer all pregnant people effective behavioral counseling interventions aimed at promoting healthy weight gain and preventing excessive GWG, based on their prepregnancy BMI [33-37]. For example, in a systematic review for the US Preventive Services Task Force (USPSTF), such interventions were associated with decreased risk of gestational diabetes mellitus (GDM), emergency cesarean birth, large for gestational age (LGA), and macrosomic infants [37]. Effective interventions involved active or supervised exercise or nutrition, diet, and physical activity. They generally started at the end of the first trimester or the beginning of the second trimester and ended near the time of birth. The duration of each intervention session, the number of sessions, the providers involved, and delivery methods (face-to-face, individual or group, computer, internet, or telephone) varied widely and a best practice could not be determined. The USPSTF did not identify any clear harms associated with behavioral counseling (eg, increase in SGA births), but data were limited and maternal anxiety and depression were increased in some studies.

Large well-designed randomized trials have illustrated the practical challenges of managing behavioral counseling and GWG at the population level. For example:

●In the LIMIT trial, over 2000 pregnant people with BMI ≥25 kg/m² were randomly assigned to usual care or a comprehensive intervention that included a combination of healthy diet, exercise, and behavioral strategies provided by a research dietician and trained research assistants [38]. GWG and almost all pregnancy outcomes (eg, preterm birth, LGA, preeclampsia, gestational diabetes) were similar for both groups; however, the intervention group had fewer births >4000 grams (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 pregnant people with obesity 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 [39]. Although the intervention group had a modest reduction in GWG (7.19 versus 7.76 kg) and reduced measures of adiposity, the primary outcomes of GDM and LGA did not differ between groups.

At the patient level, challenges to avoiding excessive GWG include sociodemographic, psychological, physical, and informational factors [40-43].

General approach

Pregnant people who appear to be achieving their GWG target — Pregnant people are encouraged to achieve the IOM/NAM 2009 GWG recommendations for their BMI group (table 2) to reduce maternal and pediatric consequences of excessive or inadequate GWG. Those who appear to be achieving their GWG target do not require intervention. (See 'Validation data' above.)

Pregnant people with a high GWG trajectory

●BMI <18.5 kg/m² – Pregnant people who were underweight before pregnancy and who appear to be on a trajectory to exceed their GWG goal are not necessarily candidates for intervention since individuals who begin pregnancy with an underweight BMI are at increased risk of an SGA birth and a higher GWG will reduce this risk.

●BMI ≥18.5 kg/m² – Pregnant people who were not underweight before pregnancy and appear to be on a trajectory to exceed their GWG goal unrelated to pathologic edema (eg, preeclampsia, heart failure, kidney disease) are encouraged to consume a healthy balanced diet and engage in regular moderate exercise. Prenatal dietary and physical activity-based lifestyle changes may help to manage GWG and are desirable behaviors regardless of pregnancy status. They have been associated with small reductions in GWG [33] and a lower risk for adverse maternal and newborn outcomes [33-35]. Behavioral counseling may be helpful in limiting ongoing excessive GWG. (See 'Behavioral counseling' above.)

Pregnant people with a low GWG trajectory

●BMI <25.0 kg/m² – Pregnant people in the underweight and normal BMI range who appear to be on a trajectory to not achieve their GWG goal are evaluated regarding their eating habits and other potential etiologies of low GWG. Low weight gain may be due to a number of factors, including but not limited to smoking, nausea and vomiting of pregnancy/hyperemesis gravidarum, medical disease, eating disorders, food insecurity, or not meeting the caloric requirements of the individual's level of activity (occupational, recreational exercise), with variable effects on fetal growth. An SGA birth is a major concern in this group [44-46]. (See 'Validation data' above.)

Management depends on the etiology, severity of the deviation from the target, and effect on fetal growth (assessed by ultrasound examination). Interventions that may be useful for patients with low GWG include optimizing the status of related underlying medical or psychiatric disorders; frequent contact with nurses, dieticians, or nutrition specialists; and, for some individuals, improved access to healthy foods. Intervention is probably not indicated if the mother is otherwise healthy and the fetus is growing appropriately.

●BMI ≥25.0 kg/m² – Pregnant people in the overweight or obese BMI range who appear to be on a trajectory to not achieve their GWG goal (eg, less than about 0.5 lb [0.23 kg] per week) do not necessarily require intervention in the absence of a medical disorder because their eating habits are not likely to increase the risk for SGA. This conclusion is supported by a 2022 meta-analysis (54 studies, over 30 million pregnancies) in which pregnant people with obesity (overall and/or separately for class I, II, and III) with GWG below IOM/NAM recommendations had no significant increase in rates of SGA, and significantly lower odds for LGA, preeclampsia, cesarean birth, postpartum weight retention, and composite neonatal morbidity [47]. A subsequent study of 11,667 pregnancies with class I obesity, 3160 with class II obesity, and 933 with class III obesity noted that 14 to 33 percent had GWG below the minimum 5 kg recommendation [48]. This did not increase risk of the adverse composite outcome in those with class I or II obesity, and reduced the risk in those with class III obesity (eg, adjusted risk ratio [aRR] 0.81, 95% CI 0.71-0.89 at weight gain z-score -2.4 corresponding to 0 kg). The adverse composite outcome included 10 maternal or infant health outcomes consistently associated with GWG below or above IOM/NAM recommendations.

Pregnant people with obesity and weight loss — Adoption of healthier lifestyle behaviors during pregnancy, which may include increased activity and/or better nutrition, may result in weight loss and should not be discouraged as long as the fetus is growing adequately on ultrasound examination. In contrast, intentional weight loss by caloric restriction or severely restricted eating is not recommended.

In a 2015 meta-analysis of six cohort studies of pregnancy outcomes among pregnant people with obesity, gestational weight loss was associated with an approximately 75 percent increase in SGA risk and 40 percent decrease in LGA risk compared with pregnant people with obesity and appropriate GWG [49]:

●SGA <10^th percentile (adjusted OR [aOR] 1.76, 95% CI 1.45-2.14) and SGA <3^rd percentile (aOR 1.62, 95% CI 1.19-2.20)

●LGA >90^th percentile (aOR 0.57, 95% CI 0.52-0.62)

●Cesarean birth (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 obesity (BMI 35.0 to 39.9 and BMI ≥40, respectively) may have more benefits than risks and may not increase the risk of SGA [50,51].

In the large study of pregnant people with class I, II, and III obesity described above (see 'Pregnant people with a low GWG trajectory' above), those with class III obesity who lost weight (z-score -2.4 to -3.0) had a greater reduction in the composite adverse outcome than those whose weight gain was positive but below the minimum 5 kg recommendation [48] However, conflating maternal and neonatal outcomes in a composite outcome measure is problematic since maternal benefits and adverse outcomes may be discordant with neonatal benefits and adverse outcomes.

Special populations

Multiple gestations — GWG in pregnant people 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'.)

Bariatric surgery — Information on pregnant people who have had bariatric surgery can be found separately. (See "Fertility and pregnancy after bariatric surgery", section on 'Gestational weight gain'.)

Eating disorders — Information on pregnant people who have an eating disorder can be found separately. (See "Eating disorders in pregnancy".)

Postpartum patients — Postpartum counseling of patients who are overweight or obese should include information on the risks of obesity and encourage 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 "Obesity in adults: Overview of management".)

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 participants), and the weight loss was maintained at 12 months postpartum in four studies [52].

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 [53].

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 5^th to 6^th 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 10^th to 12^th 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

●Prepregnancy care and counseling – Health care providers should determine a patient's body mass index (BMI) during prepregnancy office visits (calculator 1) and use this information for counseling and guiding recommendations regarding nutrition, physical activity, and weight gain/loss before, during, and after pregnancy. Prepregnancy BMI is a more important predictor of pregnancy outcome than gestational weight gain (GWG), thus it is the most important target for intervention. (See 'Prepregnancy counseling and care' above and 'LifeCycle Project weight gain recommendations' above.)

●Physiologic weight gain – Physiologic changes related to pregnancy result in a weight gain of approximately 25 lb (11 kg) at term. (See 'Physiologic weight gain in term singleton pregnancies' above.)

●GWG targets – In 2009, the Institute of Medicine (IOM, now National Academies of Sciences, Engineering, and Medicine [NAM]) made recommendations for GWG, stratified by maternal prepregnancy BMI (table 2). We generally agree with these recommendations but suggest that patients with prepregnancy obesity do not exceed the minimum IOM/NAM recommendation for GWG (5 kg). (See 'Guidance' above.)

The 2009 IOM/NAM GWG recommendations are the standard used in the United States based on validation data showing (See 'Validation data' above.):

•GWG above the IOM/NAM target range in the overall obstetric population has been associated with an increased risk of macrosomic and large for gestational age (LGA) infants, cesarean birth, pregnancy-related hypertension (gestational hypertension, preeclampsia), and gestational diabetes.

•GWG below the IOM/NAM target range in the overall obstetric population has been associated with lower birth weight and an increased risk for small for gestational age (SGA) neonates. Since birth weight is related to both maternal BMI and GWG, this risk is more significant in pregnant people who are underweight by BMI and do not achieve the IOM/NAM target range than in those with normal, overweight, or obese BMI who do not achieve the IOM/NAM target range.

●Prenatal care and counseling

•All patients – Pregnant people are encouraged to achieve the IOM/NAM 2009 GWG recommendations for their BMI group (table 2) to reduce maternal and pediatric consequences of excessive or inadequate GWG. Clinicians should monitor GWG and offer patients effective behavioral interventions aimed at promoting healthy GWG. Although recommendations for total GWG have been validated, the optimal weekly weight gain across pregnancy to achieve the GWG goal is a clinical judgment as it has not been studied extensively nor validated. (See 'Routine care' above.)

•Patients meeting their GWG target – Behavioral changes are unnecessary. (See 'Pregnant people who appear to be achieving their GWG target' above.)

•Patients with a high GWG trajectory (See 'Pregnant people with a high GWG trajectory' above.)

-For patients who were not underweight before pregnancy and do not have pathologic edema (eg, preeclampsia, heart failure, kidney disease), we encourage regular moderate exercise and consumption of a healthy balanced diet to modulate weight gain. Any birth weight benefits associated with a higher mean birth weight are offset by the increased maternal and pediatric consequences of giving birth to an LGA or macrosomic newborn.

-Patients who were underweight before pregnancy do not necessarily require intervention since they are at increased risk of an SGA birth and a higher GWG will reduce this risk.

•Patients with low GWG trajectory (See 'Pregnant people with a low GWG trajectory' above.)

-For patients in the underweight and normal BMI range, we evaluate their eating habits and other potential etiologies of low GWG. An SGA birth is a major concern in this group. Management depends on the etiology, severity of the deviation from the target, and effect on fetal growth (assessed by ultrasound examination). Interventions that may be useful for patients include optimizing the status of related underlying medical or psychiatric disorders; frequent contact with nurses, dieticians, or nutrition specialists; and, for some individuals, improved access to healthy foods. Intervention is probably not indicated if the mother is otherwise healthy and the fetus is growing appropriately.

-Patients in the overweight or obese BMI range do not necessarily require intervention in the absence of a medical disorder because their eating habits are not likely to increase the risk for SGA or other adverse pregnancy outcomes.

•Patients with obesity and weight loss – Weight loss (<5 kg during pregnancy) related to healthier life lifestyle behaviors (eg, increased activity, better nutrition) should not be discouraged as long as the fetus is growing adequately on ultrasound examination. This may lead to improved pregnancy outcomes (eg, reduced rates of preeclampsia, cesarean birth, postpartum weight retention, and composite neonatal morbidity). However, intentional weight loss by caloric restriction or severely restricted eating, especially if >5 kg, is not recommended because of the increased risk of SGA. (See 'Pregnant people with obesity and weight loss' above.)

ACKNOWLEDGMENT — 

The UpToDate editorial staff acknowledges George Macones, MD, MSCE, who contributed to an earlier version of this topic review.