The association of pregnancy and the development of obesity – results of a systematic review and meta-analysis on the natural history of postpartum weight retention

Abstract

Objective:

The magnitude of the contribution of childbearing to the development of obesity is not entirely understood. Published studies on postpartum weight retention focus on risk factors and clinical interventions. Pooled estimates of postpartum weight retention have not been reported. We summarized the existing evidence of the natural history of postpartum weight retention and estimated the extent of time after delivery that weight retention is attributable to pregnancy.

Design:

Systematic review and meta-analysis of qualitatively homogeneous studies.

Data sources:

Medline search of published studies between January 1995 and August 2005; bibliography of candidate studies.

Review methods:

Eligibility: Observational studies and control groups of randomized controlled trials. Independent review and data abstraction including study design, subject characteristics, women's weight and study quality by two reviewers. Meta-analysis of average postpartum weight retention at different points in time after delivery. Sensitivity analysis for study specific covariates using meta-regression.

Results:

Twenty-five studies describing 21 cohorts met eligibility criteria. Sixteen studies appeared homogeneous enough to be included in the meta-analysis. Average postpartum weight retention decreased continuously until 12 months postpartum (6 weeks: 2.42 (95% confidence interval (95% CI): 2.32–2.52) Body mass index (BMI), 6 months: 1.14 (95% CI: 1.04–1.25) BMI, 12 months: 0.46 (95% CI: 0.38–0.54) BMI). Postpartum weight retention was 0.46 BMI lower in studies with follow-up rate 80% at 6 weeks postpartum compared to studies with lower follow-up rate (P<0.01).

Conclusion:

Published studies consistently showed a decline in mean body weight within the first year postpartum. Data on body weight later than 12 months postpartum are scarce. The published evidence suggests a re-increase in body weight. As there are rather lifestyle-related than biological reasons for an increase in body weight after one year postpartum, we suggest using the term ‘postpartum weight retention’ exclusively within a limited period (for example, up to 12–18 months) postpartum.

Introduction

Overweight and obesity are reaching epidemic proportions, especially in the developed world. Women of childbearing age are particularly at risk for significant weight gain during their reproductive years because of biological (for example, genetic susceptibility) and behavioral (for example, smoking cessation during pregnancy, decline in physical activity after childbearing and other lifestyle alterations related to childbearing, family interactions) reasons.1, 2, 3, 4, 5, 6 Therefore, the contribution of childbearing to the development of obesity has important implications.4

Excessive weight gain during pregnancy and postpartum weight retention (PPWR) are risk factors for similar developments in subsequent pregnancies.7 Increases in body weight including PPWR contribute to the development of obesity and its adverse health sequelae. Maternal weight gain during pregnancy is associated with fetal growth and birth weight. Problems resulting from increased birth weight include dysfunctional labor, shoulder dystocia, asphyxia and consequences thereof. There also seems to be an association between gestational weight gain and the risk of pregnancy-induced hypertensive disorders, which increase the risk of infant and maternal mortality.8

A theoretical understanding of the pattern of PPWR is critical in the prevention of excessive PPWR, which can adversely affect the long-term health of women.9 A significant number of women are concerned about pregnancy having a lasting negative impact on their body weight. Pregnancy and the sedentary lifestyle that can be associated with parenting increases vulnerability to poor eating habits (for example, increased energy intake and snack eating) and exercise routines in women.10 Physical activity after pregnancy is negatively associated with the amount of PPWR. This association might be explained by increased energy expenditure but also reflects health consciousness in physically active women.10, 11, 12 On the other hand, the momentum created by weight and lifestyle trajectories before pregnancy seem to be stronger than effects of events during a time of weight fluctuation, that is pregnancy in their influence on postpartum behavior. Most women's weight, physical activity and nutrition trajectories remain identical during and after pregnancy.13

The evidence for the magnitude and duration of postpartum weight retention is limited to a few studies, which have measured postpartum weight at serial points in time. It has been reported, for example, that 80% of pregnancy-related weight gain is lost by 2–6 weeks postpartum. Other studies report that pregnancy-related weight gain is significantly decreased at 6 months postpartum.4, 14 These studies have little longitudinal data and are therefore unable to discern a pattern of PPWR. Furthermore, the specific time interval in which the measurement of PPWR best estimates the amount of weight retention attributable to pregnancy is unclear from current reports. Further, existing reviews are narrative and essentially summarize the results of individual studies.4, 15, 16 There is a lack of reviews providing quantitative synthesis and pooled estimates of weight retention over time. In this systematic review, we identify relevant studies of postpartum weight retention, derive pooled estimates of PPWR at various time intervals after delivery, and attempt to outline a pattern of PPWR.

Materials and methods

Study design and eligibility criteria

We conducted a systematic review in which we searched MEDLINE for studies on PPWR during the period January 1995 to August 2005 using combinations of keywords related to weight (weight, overweight, obesity, weight retention, body mass index (BMI), weight gain in title); the postpartum period (postpartum, puerperium, maternal, pregnancy in title); and study design (study, trial in title/abstract). We limited the search to papers with English-language abstract. We conducted a handsearch of the reference lists of eligible articles as well as those of review articles to identify additional studies. Studies were selected for inclusion based on three primary criteria: (1) quantitative information on PPWR (directly or indirectly); (2) information on time period since delivery when postpartum weight was assessed and (3) a fixed follow-up time period. Studies that reported PPWR in women who had undergone dietary or exercise interventions were excluded. Only original data from observational studies and the control groups of RCT with at least 10 women were considered. We contacted the authors of articles when it appeared that relevant data may have been collected but not reported in the published study.

Identification of articles and data abstraction

We reviewed the abstracts of all 436 citations located, excluded 411 articles because they did not focus on PPWR or did not meet the eligibility criteria. (Figure 1) Two investigators (NS, JS) independently searched, reviewed and abstracted data.

Figure 1
figure1

Study identification and selection.

Data were abstracted using a standardized data abstraction form, which had been pilot tested for this systematic review. The form included information on study design, sample size, country in which the study was completed, participant characteristics (age, race, parity, smoking status, educational level and gestational age at delivery). Specific data collected on weight retention included the time intervals during which weight was assessed (baseline, time during pregnancy and postpartum), the amount of weight retention measured in mean and s.d., the range of weight in BMI, the method by which weight measurements were obtained (directly measured, self-reported, abstracted from medical records), and the follow-up rate of participants. Weight data reported in kilograms or pounds were converted to BMI.

Assessment of study quality

Study quality was assessed based on: (1) study type, (2) participant follow-up rate, (3) likelihood of bias in weight measurement (self-report or actual measurement) and (4) quality of baseline weight data.17 Two authors (NS, JS) rated the quality of each study. A third reviewer (WN) was designated to render a final decision if the initial two reviewers were unable to reach consensus.

Data synthesis and statistical analyses

Qualitatively homogeneous studies were pooled and stratified by the point in time of postpartum weight measurement. We derived pooled means for PPWR with 95% confidence intervals (95% CI) for different time periods. Pooled estimates were calculated using the inverse variance method (fixed effects model).17, 18, 19

We calculated weight distributions (that is mean and s.e. of the BMI) if these data were not reported. The delta method was used for converting data from kilogram to BMI if data on PPWR were reported in pounds or kilograms.20 The delta method requires mean, s.d. and sample size from weight and height data as well as the covariance of weight and height (assumed to be 0.8) in the study sample. The necessary information was obtained from all 16 studies.

Heterogeneity based on the following covariates (follow-up rate, likelihood of bias in weight measurement, mean age) was examined using meta-regression.17, 19 This was carried out separately for studies with PPWR assessments at 6 weeks and 6 months postpartum. At these two points in time most data were available. Meta-analysis was performed using Stata statistical software 8.0 for windows.19, 21

Results

Qualitative results

Twenty-five studies met our inclusion criteria and were considered for data abstraction.22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46 Because of multiple publications of identical cohorts, we limited our analysis to 21 cohorts of women. These 21 studies were included in the systematic review (Figure 1).

Twenty-one studies including 7582 women were analyzed. Tables 1, 2 and 3 summarize the results of the qualitative analysis. Fifteen prospective studies,23, 24, 29, 30, 31, 32, 33, 34, 35, 36, 38, 40, 41, 42, 43, 44, 45 five retrospective studies,22, 25, 26, 27, 28, 37, 46 and the control group from a randomized controlled trial39 were included in the final analysis. Studies in which women were recruited around the time of delivery and then followed prospectively for postpartum body weight (ambivalent design, as baseline weight was assessed retrospectively)24, 29, 30, 34, 35, 36, 44, 45, 46 were considered as prospective in design, as we wanted to focus on the development of postpartum weight change.

Table 1 Summary of study characteristics
Table 2 Summary of weight data
Table 3 Summary of quality criteria and scores for each study

The majority of studies were conducted in North America22, 23, 24, 29, 35, 37, 38, 39, 40, 42, 45, 46 and Europe,25, 26, 27, 28, 34, 36, 41, 43 where the magnitude of weight retention among women appears to be similar.39 In developing countries, women retain less weight after pregnancy compared with women in developed countries. Two studies were conducted in Brazil31, 32, 33 and China.44 Although these studies included different populations, they did not compromise overall homogeneity as the Brazilian study reported mean reduction rates in weight retention similar to European studies.25, 26, 27, 28, 31, 32, 33, 34, 36, 41, 43 The study participants in the study conducted in China recruited middle class women.44 (Table 1) All but one34 study were published in English language.22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46

The study populations were mainly recruited from inpatients in departments of obstetrics.24, 25, 26, 31, 32, 33, 35, 36, 38, 39, 40, 41, 42, 43, 44, 45, 46 There was a higher percentage of low-income women in the studies conducted in North America, but socio-economic status was thought to be homogeneous across studies.35, 37, 39, 42, 45, 46 The sample size varied between 47 and 1423 women. Six studies had small sample sizes (<100 women).23, 27, 28, 35, 39, 41, 46 Four studies had sample sizes of over 500 women.24, 36, 38, 40 Studies were judged homogeneous regarding participants' age. Most studies included primarily adult women.23, 27, 28, 29, 31, 32, 33, 35, 36, 38, 43, 46 Four studies reported a mean age above 30 years,23, 27, 28, 36, 46 one study below 20 years.42 Two studies did not provide any information on their population's age24, 44 (Table 1).

One study only included Caucasians,37 one only African Americans,35 one only women from China.44 Ten studies preponderantly included white women.25, 26, 27, 28, 29, 30, 34, 36, 38, 40, 41, 43 Only one36 of the European studies reported the ethnicity of their cohort. We assume that the women in the other European studies and in the Australian study were predominantly white.25, 26, 27, 28, 34, 41, 43 The population of eight studies consisted of different ethnical groups22, 23, 24, 31, 32, 33, 39, 42, 45, 46 (Table 1).

Two studies only included nulliparae.30, 35 Mean gestational age ranged between 39.0 and 40.1 weeks24, 25, 26, 37, 39, 41, 43, 44, 45 (Table 1).

Gestational weight gain was measured in nine23, 36, 37, 38, 39, 41, 42, 43, 44 and self-reported in six studies.22, 27, 28, 29, 34, 35, 45 Excluding studies in which gestational weight gain was measured at 36 weeks gestation or earlier,23, 39, 41, 42 the mean gestational weight gain was in the expected range, between BMI 4.736 and BMI 6.535 (Table 2).

As there is already significant maternal weight gain in the first trimester, we considered studies that did not use prepregnant weight data, but first trimester weight as baseline25, 26, 27, 28, 38, 40, 41 to be too heterogeneous from the others to be included in the meta-analysis.15 Stein et al.42 provided data on prepregnant body weight and weight at 17 weeks gestation and reported an increase from BMI 22.8 to 24.2. In five studies23, 38, 40, 41, 42 baseline weight was measured, but only one study23 provided measured prepregnant body weight. Four authors abstracted information on baseline weight from medical records but did not provide information whether the weight was measured or self-reported.25, 26, 27, 28, 37, 43 Recalled pregravid weight is most often used to estimate gestational weight gain and PPWR. Only Polley et al. specified prepregnant weight as weight during the last menstrual period.39

Study quality assessment

Study quality is summarized in Table 3. Overall, 12 studies23, 29, 30, 31, 32, 33, 34, 35, 36, 37, 39, 42, 43, 45 were rated good quality, six22, 24, 38, 40, 44, 46 moderate quality and three studies25, 26, 27, 28, 41 fair quality. The majority of studies had follow- up rates of 80% or more.22, 23, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 37, 38, 40, 42, 43, 45, 46 In prospective studies and in the randomized controlled trial, the percentage of women lost to follow-up ranged between 60 (at 15 years postpartum)36 and 0%.23, 34, 42, 45 Although measured prepregnant and postpartum weight may be most accurate to evaluate PPWR, there are consistent data on the reliability of self-reported weight. We considered studies in which the method of weight assessment (for example, self-reported and measured) was identical at baseline and postpartum most reliable. Bias in weight assessment was unlikely in seven studies23, 30, 35, 36, 37, 39, 43 (Table 3).

Except the five studies that did not provide data on prepregnant weight,25, 26, 27, 28, 38, 40, 41 all studies were considered homogeneous enough to be included in the meta-analysis.22, 23, 24, 29, 30, 31, 32, 33, 34, 35, 36, 37, 39, 42, 43, 44, 45, 46

Quantitative results

The included studies obtained information on body weight at a variety of different points in time after delivery. Most of the data are within 6 months after delivery. Two authors reported weight at 9 months,22, 31, 32, 33 three at 1 year,29, 34, 36 and another two at 18 months postpartum.29, 43 Later measurements were at 15 years36 postpartum.

In 50% of the studies included in the meta-analysis (n=8), postpartum body weight was measured at a single point in time.22, 24, 30, 37, 39, 43, 45, 46 The remaining studies provided two or more body weight assessments.23, 29, 31, 32, 33, 34, 35, 36, 42, 44 Figure 2 shows the course of postpartum weight change in studies with at least two postpartum weight measurements. Within the first year after delivery, mean postpartum weight consistently declined in all cohorts studied23, 29, 31, 32, 33, 34, 35, 42, 44 (Figure 2). Only two of the eight studies with data on two or more postpartum weight measurements assessed body weight later than 1 year postpartum.29, 36 In these two cohorts an increase in mean postpartum weight was reported after 12 months postpartum29, 36 (Figure 2).

Figure 2
figure2

Quantitative results: mean absolute postpartum weight retention in included studies with two or more postpartum weight assessments. *Indicates measurements are not connected because of long time interval. BMI, body mass index.

Figure 3 shows the absolute postpartum weight retention (mean, 95% CI) in all studies included in the meta-analysis stratified by time after delivery. Unlike prepregnant body weight, postpartum weight was mostly measured. Four studies provided self-reported body weights at all postpartum assessments.30, 35, 43, 46 It is not clear whether data abstracted from medical records were measured or self-reported37(Table 2).

Figure 3
figure3

Absolute postpartum weight retention in BMI (mean and 95%-CI) in studies included in the meta-analysis stratified by time after delivery. *Indicates the data are arranged in time blocks that are not spaced commensurately. BMI, body mass index.

The mean weight of women in different studies was, on average, 7–13% higher in the first postpartum month than at baseline. The average relative PPWR decreased until 12 months after delivery. At 12 months postpartum the average relative weight retention ranged from 1 to 5%.29, 34, 36 After month 12 the average weight tended to increase again.

The means and 95% CI of the pooled estimates of average absolute PPWR in BMI are graphically displayed in Figure 4. The pooled average absolute weight retention decreased from 2.42 (95% CI 2.32–2.52) BMI in the first 6 weeks after delivery, to 1.14 (95% CI 1.04–1.25) BMI at 6 months, and to 0.46 (95% CI 0.38–0.54) BMI at 12 months postpartum. After that point in time the average weight increased again (Figure 4, Table 4).

Figure 4
figure4

Pooled mean absolute postpartum weight retention in BMI (mean and 95% CI) stratified by time after delivery. *Indicates the data are arranged in time blocks that are not spaced commensurately. BMI, body mass index.

Table 4 Results of the meta-analysis: pooled absolute postpartum weight retention stratified by time of postpartum weight assessment

Sensitivity analysis by means of meta-regression showed a significant influence of follow-up rate on PPWR both at the 6 weeks and the 6 months measurements. PPWR was significantly lower in studies with follow-up rates of 80% compared to studies with lower follow-up rates. PPWR at 6 weeks postpartum was 0.46 BMI lower in studies with higher follow-up rates (80%; P<0.01). At 6 months postpartum PPWR was 1.63 BMI lower in studies with follow-up rates 80% (P<0.01). Likelihood of bias in weight measurement and mean age of study participants had no significant influence on PPWR.

Discussion

In the present analysis, there is a steep decrease in PPWR in the first 3 months after delivery. We further found a continuous decrease in PPWR until 12 months postpartum.

Physiologically, most of the pregnancy-related weight components (that is infant weight, placenta, amniotic fluid) are lost within the first days after delivery. At 6 weeks postpartum excess fluids gained during pregnancy are lost.37 After that PPWR is attributable mainly to increases in body fat.31 Most authors reported changes in body weight only until 6 months postpartum.23, 24, 30, 35, 37, 39, 41, 42, 44 The three studies that assessed body weight two times between 6 and 12 months postpartum consistently found a decrease in PPWR within that timeframe.29, 31, 32, 33, 34 Data on body weight after more than 12 months postpartum are scarce. Only one study assessed PPWR at several points in time after delivery until 18 months postpartum.29 Women in this cohort steadily lost body weight until 12 months postpartum. Between 12 and 18 months postpartum, however, an increase in mean body weight was observed.29 There are no physiological or biological explanations to link pregnancy to the observed weight gain after 12 months postpartum.29 Environmental and lifestyle factors are much more likely to explain why women seem to gain weight after about 12 months postpartum.5, 6, 10, 11 Therefore, it should be critically discussed whether the term ‘postpartum weight retention’ is appropriate for differences between prepregnant weight and weight more than about 12 months postpartum. On the basis of results of our meta-analysis, we propose to use the term ‘postpartum weight retention’ only for weight retention within a limited postpartum period, for example up to 12 or 18 months postpartum. However, because the data are limited, this definition can only be preliminary. A large and well-conducted study with several measurements – for example until 2 years postpartum – is necessary to confirm our findings.

Several studies have consistently shown that self-reported measurements underestimate the true weight by BMI 0.2–0.3 on average.4, 8, 47 Assuming an underestimation of BMI 0.25 in the baseline weight due to self-reported data, almost all pregnancy-related weight is lost by 12 months postpartum (BMI 0.46–BMI 0.25=BMI 0.21).5 If, in addition, estimates of weight gain among non-pregnant women of childbearing age, which vary between BMI 0.04 and BMI 0.35 per year are considered, the female population appears to lose (almost) all pregnancy-related weight gain by approximately 12 months (between 9 and 18 months) postpartum.4, 36, 47 Therefore, from our data, we conclude that pregnancy should no longer be regarded as a global factor contributing to the development of overweight and obesity in the female population.15 A subgroup of women, however, has PPWR critically above the average values presented in our analysis.38, 48 Several publications already focused on risk factors of body weight changes after pregnancy. According to a review by Gunderson and Abrams,4 these include prepregnant weight, parity, lactation, physical activity and other lifestyle factors. Women with excessive PPWR are at risk for later obesity. Obesity adversely affects the health status by leading to comorbid conditions such as cardiovascular diseases, diabetes, osteoarthritis, cancer and reduced fertility.4, 15, 16, 49, 50 In addition, obesity results in a 2- to 3-fold increased mortality among women.4, 51, 52 The economic costs attributed to excess body fat and its consequences are second only to smoking.49

Validity of findings

There are three arguments in favor of the validity of the presented results concerning the natural history of PPWR.

We have excluded five studies from the quantitative analysis because they did not provide data on prepregnant weight.25, 26, 27, 28, 38, 40, 41 In these studies, baseline weight was assessed within the first trimester of pregnancy. PPWR is suspected to be lower in studies excluded because of inflated baseline weight. At 6 weeks postpartum, Soltani and Fraser41 reported a mean PPWR of 1.0 BMI (pooled mean at 6 weeks postpartum 2.4 BMI). At 6 months, mean PPWR was 0.3 BMI40 and 0.4 BMI41 in studies with first trimester baseline weight compared to 0.8 BMI34 to 3.0 BMI35 in studies with baseline weight assessments before pregnancy. At 12 months postpartum, mean weight retention in the study excluded in the quantitative analysis (0.6 BMI38) was within the range of PPWR in included cohorts (0.4 BMI34 to 1.0 BMI29) (Figures 3 and 4). Overall, the findings in studies excluded from the meta-analysis are consistent with the quantitative results.

Findings from studies with at least two postpartum weight assessments are also consistent with our pooled estimates. Both within and between cohorts of women postpartum weight declined within the first months postpartum and tended to increase again after about 12 months. However, we want to emphasize that the data on late follow-up (at least 1 year) are scarce, so that our findings should be interpreted with caution.

Interestingly, meta-regression showed that PPWR was significantly lower in studies with follow-up rates of 80% compared to studies with lower follow-up rates. This implies that women with low PPWR were more likely to be lost to follow-up. Consequently, true PPWR is suspected to be even lower than our pooled estimates, so that the presented data can be interpreted as a conservative estimate of the true natural history of PPWR.

Limitations

Our review has some limitations. Overall quality of most pooled studies was at least moderate, and these studies were judged homogeneous in the qualitative analysis (Table 3). Reporting bias cannot be excluded, as we did not consider articles without an English-language abstract for this review. Another possible drawback is that the data on PPWR were not distributed equally across the postpartum period. The digit preference to weights ending in 0 or 5 when asked about a general estimate of weight (prepregnancy), rather than about a particular weight measurement (for example, at the time of the last menstrual period),35 adds to the heterogeneity between self-reported and measured prepregnant body weight.

We decided to report the quantitative results in BMI as the unit of weight change. Although kilograms might be more intuitive for some readers, the advantage of BMI over kilogram is that it adjusts for height and is therefore less influenced by ethnical heterogeneity in the study populations. Performing the meta-analysis with kilogram data as the unit of weight change did not alter our conclusions (data not shown, but can be obtained from the corresponding author upon request).

From the presented analysis, information concerning the individual woman's PPWR is not inferable. As Janney et al.29 reported, the pattern of weight retention varies considerably. The upper limit of the 95% CI of mean PPWR is not necessarily an adequate limit under which postpartum weight of an individual woman should be. It may only be a rough estimate for individual interventions.

Studies included in the meta-analysis were heterogeneous in terms of parity. However, we do not think that this has biased our quantitative results, as primiparae and multiparae do not seem to gain more weight during pregnancy compared to nulliparae.15, 53, 54

Walker et al.45 reported that ethnic differences in weight retention may emerge between 6 weeks and 6 months postpartum. The weight loss in women included in the study by Lederman et al., which is the only study that exclusively focused on African-American women, appears to be less pronounced compared to studies including predominantly Caucasian women.23, 29, 34 However, our data do not provide sufficient evidence to conclude that African-American women show significantly different patterns of PPWR.

Implications for future research

Our meta-analysis is the first to provide an estimation of the natural history of PPWR based on the existing evidence. The presented data are a necessary prerequisite to define what ‘excessive postpartum weight retention’ at different points in time after delivery refers to. Our study provides information that may help to decide on ‘whom to target when’. This is especially important to increase the efficiency of existing intervention and prevention programs. We suggest targeting primarily women with postpartum weight retention much greater than the pooled average in weight reduction campaigns. To identify women at risk, body weight may be measured during visits at gynecologists or pediatricians during preventive medical checkups. Alternatively, midwives could screen women's weight at specific points in time after delivery. The problem of excessive PPWR in a subgroup of women may require multilevel interventions and day-to-day interactions with the patients.9 It is critically important to overcome barriers in lifestyle change to decrease the high drop-out rates in intervention programs targeted at postpartum women who are obese or at increased risk for later obesity.48

As pregnancy and childbearing are major life events, women at risk for excessive PPWR might be receptive to prevention programs focusing on behavior changes in the postpartum period.11 On the basis of a broad consensus of all stakeholders (researchers, clinicians, health policy leaders, patients and so on) a defined point in time after delivery at which women should be screened for excessive PPWR needs to be established.

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Acknowledgements

We thank Joanna Brzeska for translating the article by Kanadys et al. (1998). She did not receive money for her assistance.

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Correspondence to N M Schmitt.

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Conflict of interest

All authors hereby give consent to publication of this manuscript in the International Journal Of Obesity. None of the contributing authors received any funding for this work or has any other competing interests (that is relevant patents, financial and business relationships to sponsors, companies related to the research or the outcome of the studies in the manuscript) to declare.

Natalie M Schmitt: Conception, design, literature search, data abstraction, interpretation of data, drafting the manuscript, final approval of the manuscript to be published. Wanda K Nicholson: Conception, interpretation of data, revision of the manuscript, final approval of the manuscript to be published. Jochen Schmitt: Conception, literature search, data abstraction, interpretation of data, statistical analysis, revision of the manuscript, final approval of the manuscript to be published.

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Schmitt, N., Nicholson, W. & Schmitt, J. The association of pregnancy and the development of obesity – results of a systematic review and meta-analysis on the natural history of postpartum weight retention. Int J Obes 31, 1642–1651 (2007). https://doi.org/10.1038/sj.ijo.0803655

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Keywords

  • body mass index
  • meta-analysis
  • natural history
  • postpartum weight retention
  • pregnancy

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