Abstract
Objective
This study aimed to assess the association of maternal body mass index (BMI) with a composite of severe maternal outcomes.
Study Design
Secondary analysis of a cohort of deliveries on randomly selected days at 25 hospitals from 2008 to 2011. Data on comorbid conditions, intrapartum events, and postpartum course were collected. The reference group (REF, BMI: 18.5–29.9 kg/m2), obese (OB; BMI: 30–39.9 kg/m2), morbidly obese (MO; BMI: 40–49.9 kg/m2), and super morbidly obese (SMO; BMI ≥ 50 kg/m2) women were compared. The composite of severe maternal outcomes was defined as death, intensive care unit (ICU) admission, ventilator use, deep venous thrombosis/pulmonary embolus (DVT/PE), sepsis, hemorrhage, disseminated intravascular coagulation (DIC), unplanned operative procedure, or stroke. Patients in the REF group were matched 1:1 with those in all other obesity groups based on propensity score using the baseline characteristics of age, race/ethnicity, previous cesarean, preexisting diabetes, chronic hypertension, parity, cigarette use, and insurance status. Multivariable Poisson’s regression was used to estimate adjusted relative risks (aRRs) and 95% confidence intervals (CIs) for the association between BMI and the composite outcome. Because cesarean delivery may be in the causal pathway between obesity and adverse maternal outcomes, models were then adjusted for mode of delivery to evaluate potential mediation.
Results
A total of 52,162 pregnant patients are included in the analysis. Risk of composite maternal outcomes was increased for SMO compared with REF but not for OB and MO [OB: aRR = 1.06, 95% CI: 0.99–1.14; MO: aRR = 1.10, 95% CI: 0.97–1.25; SMO: aRR 1.32, 95% CI: 1.02–1.70]. However, in the mediation analysis, cesarean appears to mediate 46% (95% CI: 31–50%) of the risk of severe morbidity for SMO compared with REF.
Conclusion
Super morbid obesity is significantly associated with increased serious maternal morbidity and mortality; however, cesarean appears to mediate this association. Obesity and morbid obesity are not associated with maternal morbidity and mortality.
Keywords: obesity, maternal morbidity, cesarean delivery, propensity score analysis
Obesity is a serious public health concern and has been increasing in the United States and elsewhere over the last few decades.1–5 The prevalence of obesity in adults, defined as a body mass index (BMI) ≥ 30 kg/m2, has increased from 15% during 1976 to 1980 to 36% during 2009 to 2010.1,2 The prevalence of morbid obesity (MO; BMI ≥ 40 kg/m2) and super morbid obesity (SMO; BMI ≥ 50 kg/m2) has increased in a similar fashion, although more so in men than in women.4 Recent data suggest that 7.6% of adults are now MO (BMI ≥ 40 kg/m2).6 Similar concerns have been raised in the obstetric population, with over 50% of pregnancies now complicated by overweight or obesity (OB; BMI ≥ 25.0 kg/m2).7 The prevalence of obesity in women of childbearing age increased from 7.4% in 1976 to 30.5% in 2018, and the prevalence of overweight/OB rose from 22.8 to 53.5% over a similar time period.8,9 Excess weight gain in the OB population compounds these risks.10 Prepregnancy and early pregnancy obesity, in particular, have been associated with increased rates of miscarriage, congenital anomalies (particularly neural tube defects), fetal macrosomia, perinatal death, gestational diabetes, preeclampsia, postterm pregnancy, postpartum hemorrhage, thromboembolism, and wound infection.11–20 Previous studies have also shown that the risks of prolonged labor, failed induction, and cesarean delivery are increased in OB women.11–15,21 Mean birth weight is higher and large for gestational age is more frequent in neonates born to OB mothers.11,12,16
Because super morbid obesity (BMI ≥ 50 kg/m2) is less common, less is known about the magnitude of risks in that population. A recent study has suggested that women with a BMI of 60 kg/m2 or higher are at increased risk for maternal complications when compared with women with lesser degrees of obesity.22
We hypothesized that the risk of severe maternal morbidity or mortality increases as the degree of obesity rises, with women with SMO at the highest risk. We analyzed a large cohort of over 100,000 well-characterized pregnancies delivering at hospitals participating in the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU) Network (See Supplementary Appendix A [available in the online version] for a list of other members of the NICHD MFMU Network.). The aim of this study is to evaluate whether OB, MO, and SMO women are at progressively elevated risk for severe maternal morbidity or mortality. We also sought to determine whether cesarean delivery mediates this association.
Materials and Methods
This study is a secondary analysis of a cohort of deliveries occurring on randomly selected days at 25 hospitals from 2008 to 2011.23,24 Patients who arrived on the selected days and who delivered at 24 weeks’ gestation or above with a live fetus at admission were included. Maternal and neonatal charts were reviewed by trained and certified abstractors. Demographic data, as well as detailed medical and obstetric histories, intrapartum, and postpartum care, and obstetric and neonatal outcomes, were collected. Maternal data were collected until hospital discharge and neonatal data were collected until discharge or 120 days of life whichever came first. The study was approved by the institutional review board at each participating institution, under a waiver of informed consent. Additional details of the study design have been previously published.23,24
The current analysis includes women with singleton deliveries ≥ 24 weeks’ gestation. Maternal BMI was calculated using maternal height and most recent weight prior to delivery, as prepregnancy or early pregnancy weight was not available for a majority of the subjects. The reference group (REF) was defined as a BMI of 18.5 to 29.9 kg/m2, OB as a BMI of 30 to 39.9 kg/m2, MO as a BMI of 40 to 49.9 kg/m2, and SMO as a BMI ≥ 50 kg/m2. The composite of severe maternal outcomes was defined as death, intensive care unit (ICU) admission, ventilator use, deep venous thrombosis/pulmonary embolus (DVT/PE), sepsis, hemorrhage (as indicated by the provider in the chart), disseminated intravascular coagulation (DIC), unplanned operative procedure, or stroke. Unplanned procedures included repairs of bladder and bowel injuries, uterine artery ligation or embolization, wound explorations and repairs, and cardiopulmonary resuscitation.
Due to statistically significant differences in baseline characteristics, we conducted a propensity score analysis where patients in the REF group were matched to those in the OB, MO, and SMO groups based on maternal age (≤19, 20–34, ≥35 weeks), preexisting diabetes (yes/no), chronic hypertension (yes/no), race/ethnicity (non-Hispanic White, non-Hispanic Black, non-Hispanic Asian, Hispanic, and other/not documented), parity (nulliparous or multiparous), government insurance (yes/no), prior cesarean (yes/no), and tobacco use during the current pregnancy (yes/no). For purposes of matching, women in the REF group were considered unexposed and all other groups were considered exposed. All women were assigned a propensity score based on baseline characteristics. Those in each of the groups considered exposed were matched to the unexposed REF group in a 1:1 ratio where scores differed by no more than 0.01. Individuals were excluded if no match was found. Unexposed individuals were also excluded if they were a duplicate match for an exposed individual. We then evaluated the frequency of baseline demographic characteristics and maternal complications by BMI category using the Cochran–Armitage for discrete variables, the Jonckheere–Terpstra for continuous variables, and score tests for trend. Adjusted relative risks (aRRs) and 95% confidence intervals (CIs) were estimated with multivariable Poisson’s regression models for the composite outcome, controlling for potentially confounding factors. Because significant group differences remained for age, chronic hypertension, and preexisting diabetes after propensity score matching, these variables were also included in initial multivariable models. For parsimony, thefinal models include only those variables that were significant. Because cesarean delivery is in the causal pathway between BMI and severe maternal morbidity, we conducted a mediation analysis using PROC Causalmed to estimate the percent of the risk of maternal morbidity that may be mediated by cesarean delivery.
SAS 9.4 was used for the analyses. A two-tailed p-value of less than 0.05 was considered statistically significant. Imputation for missing data was not performed.
Results
Between March 2008 and February 2011, data were collected on 115,502 women in 25 hospitals. Of these, 52,162 women with singleton deliveries ≥ 24 weeks’ gestational age and a BMI ≥ 18.5 kg/m2 based on last recorded weight were included in the propensity analysis (Fig. 1). Overall, 26,081 (50%) were included in REF, 21,704 (41.6%) were OB, 3,787 (7.3%) were MO, and 590 (1.1%) were SMO. Patient demographics and comparisons between groups are shown in Table 1. Compared with REF women, as BMI increased, maternal age decreased. There was a significant trend toward non-Hispanic Black race and ethnicity and smoking with increasing obesity, but OB, MO, and SMO women were all less likely to use alcohol or illicit drugs. There was also a significant trend toward the presence of chronic hypertension or pregestational diabetes as BMI increased. Lastly, OB, MO, and SMO women were increasingly less likely to be pregnant as a result of assisted reproductive technology as compared with the REF.
Fig. 1.
Study population. BMI, body mass index; GA, gestational age.
Table 1.
Patient demographics by BMI category at delivery
| Reference (REF) | Obese (OB) | Morbidly obese (MO) | Super morbidly obese (SMO) | |
|---|---|---|---|---|
| n = 26,081 | n = 21,704 | n = 3,787 | n = 590 | |
| Maternal age (wk) | 27.9 ± 6.3 | 28.1 ± 6.0 | 27.9 ± 5.9 | 27.9 ± 5.8 |
| Age (y) | 4,356 (16.7) | 3,258 (15.0) | 523 (13.8) | 83 (14.1) |
| ≤19 | 2,310 (8.9) | 1,656 (7.6) | 263 (6.9) | 42 (7.1) |
| 20–34 | 19,415 (74.4) | 16,790 (77.4) | 3,001 (79.2) | 465 (78.8) |
| ≥ 35 | 4,356 (16.7) | 3,258 (15.0) | 523 (13.8) | 83 (14.1) |
| Nulliparous | 9,944 (38.1) | 8,419 (38.8) | 1,456 (38.5) | 230 (39.0) |
| Prior cesarean | 4,869 (18.7) | 3,770 (17.4) | 811 (21.4) | 145 (24.6) |
| Race/ethnicity | ||||
| NH White | 10,657 (40.9) | 9,383 (43.2) | 1,556 (41.1) | 194(32.9) |
| NH Black | 6,449 (24.7) | 4,701 (21.7) | 1,252 (33.1) | 262 (44.4) |
| NH Asian | 739 (2.8) | 668 (3.1) | 32 (0.8) | 6 (1.0) |
| Hispanic | 6,730 (25.8) | 5,854 (27.0) | 799 (21.1) | 101 (17.1) |
| Other/Nd | 1,506 (5.8) | 1,098 (5.1) | 148 (3.9) | 27 (4.6) |
| Prior preterm birth | 2,433 (9.3) | 1,838 (8.5) | 382 (10.1) | 73 (12.4) |
| Pregestational diabetes | 326 (1.3) | 182 (0.8) | 80 (2.1) | 26 (4.4) |
| Chronic hypertension | 602 (2.3) | 342 (1.6) | 176 (4.7) | 61 (10.3) |
| Cigarette use | 3,110 (11.9) | 1,906 (8.8) | 470 (12.4) | 76 (12.9) |
| Alcohol use | 901 (3.5) | 605 (2.8) | 109 (2.9) | 18 (3.1) |
| Drug use | 1,250 (4.8) | 637 (2.9) | 139 (3.7) | 25 (4.2) |
| Government insurance | 11,397 (43.7) | 8,542 (39.4) | 1,880 (49.6) | 347 (58.6) |
| Anticoagulation | 203 (0.8) | 153 (0.7) | 49 (1.3) | 7 (1.2) |
| ART | 318 (1.2) | 237 (1.1) | 33 (0.9) | 4 (0.7) |
Abbreviations: ART, assisted reproductive technology; BMI, body mass index; Nd, not documented; NH, non-Hispanic.
Notes: Data presented are mean ± standard deviation) or n (%).
Missing: alcohol use (51), drug use (74), ART (25).
As shown in Table 2, intrapartum and postpartum complications progressively increased as the BMI increased. OB, MO, and SMO women were more likely to have gestational diabetes and preeclampsia/eclampsia was significantly more frequent. Labor induction was also increasingly more common with increasing obesity, as was a failed induction. The rate of cesarean delivery also increased as the degree of obesity increased, with over half (52.7%) of SMO requiring cesarean delivery. The likelihood of a failed trial of labor following a prior cesarean birth also increased significantly with increasing BMI, with frequencies ranging from 60.2% in the OB group to a high of 71.8% in the SMO group, compared with 52.4% in the REF group (p-value for trend <0.001). Increasing BMI was also associated with increasing frequencies of suspected chorioamnionitis and postpartum endometritis. Maternal death was rare in all categories.
Table 2.
Intrapartum and postpartum complications by BMI category at delivery
| Reference (REF) | Obese (OB) | Morbidly obese (MO) | Super morbidly obese (SMO) | p-Value for trenda | |
|---|---|---|---|---|---|
| n = 26,081 | n = 21,704 | n = 3,787 | n = 590 | ||
| Gestational diabetes | 1,051 (4.0) | 1,542 (7.1) | 447 (11.8) | 70 (11.9) | <0.001 |
| Malpresentation | 1,029 (4.0) | 809 (3.7) | 193 (5.1) | 29 (5.0) | 0.06 |
| Amniotic fluid abnormalityb | 1,170 (4.5) | 1,068 (4.9) | 249 (6.6) | 51 (8.6) | <0.001 |
| Preeclampsia/eclampsia | 1,055 (4.1) | 1,362 (6.3) | 445 (11.8) | 95 (16.1) | <0.001 |
| Labor induction | 6,057 (23.2) | 6,494 (29.9) | 1,419 (37.5) | 234 (39.7) | <0.001 |
| Failed induction | 998 (3.8) | 1,590 (7.3) | 483 (12.8) | 106 (18.0) | <0.001 |
| Failed trial of labor following prior cesarean delivery | 1,114 (52.4) | 820 (60.2) | 153 (61.5) | 28 (71.8) | <0.001 |
| Shoulder dystocia | 386 (1.5) | 500 (2.3) | 106 (2.8) | 11 (1.9) | <0.001 |
| Cesarean delivery | 7,197 (27.6) | 7,191 (33.1) | 1,711 (45.2) | 311 (52.7) | <0.001 |
| Suspected Chorioamnionitisc | 926 (4.1) | 982 (5.4) | 176 (5.9) | 16 (3.7) | <0.001 |
| Wound complicationd | 48 (0.7) | 35 (0.5) | 12 (0.7) | 6 (1.9) | 0.42 |
| Endometritis | 109 (0.4) | 136 (0.6) | 25 (0.7) | 4 (0.7) | 0.002 |
| Preterm delivery | 3,062 (11.7) | 1,889 (8.7) | 458 (12.1) | 73 (12.4) | <0.001 |
Abbreviation: BMI, body mass index.
Notes: Data presented are n (%).
Missing: malpresentation (140), AF abnormality (35), preeclampsia/eclampsia (3), labor induction (1), failed induction (1), failed trial of labor (569), shoulder dystocia (1), endometritis (1).
Cochran–Armitage test for trend.
Oligohydramnios or polyhydramnios.
Limited to women in labor.
Among those with cesarean delivery.
The individual components of the composite outcome, as well as the composite outcome are shown in Table 3. Although individual components were uncommon, overall 3,306 (6.3%) of patients experienced the composite outcome. The composite outcome was progressively more frequent in OB (6.4%), MO (7.5%), and SMO (9.5%) as compared with REF (6.1%; p-value for trend <0.001). In linear regression models, a 5-unit increase in BMI resulted in an increase of 0.012 in the relative risk of the composite outcome, adjusting for preeclampsia/eclampsia, chronic hypertension, and cesarean delivery (not shown).
Table 3.
Maternal composite outcome and components by BMI category at delivery
| Reference (REF) | Obese (OB) | Morbidly obese (MO) | Super morbidly obese (SMO) | p-Value for trenda | |
|---|---|---|---|---|---|
| n = 26,081 | n = 21,704 | n = 3,787 | n = 590 | ||
| Composite serious morbidity | |||||
| n (%) | 1,436 (5.5) | 1,311 (6.0) | 263 (6.9) | 52 (8.8) | < 0.001 |
| Composite components | |||||
| Hemorrhage | 1,269 (4.9) | 1,147 (5.3) | 227 (6.0) | 43 (7.3) | |
| Sepsis | 10 (0.04) | 10 (0.05) | 3 (0.08) | 1 (0.2) | |
| DIC | 20 (0.08) | 3 (0.01) | 3 (0.08) | 0 | |
| DVT/PE | 5 (0.02) | 7 (0.03) | 2 (0.05) | 1 (0.17) | |
| Stroke | 9 (0.03) | 17 (0.08) | 3 (0.08) | 0 | |
| ICU admission | 155 (0.6) | 121 (0.6) | 36 (1.0) | 8 (1.4) | |
| Ventilator use | 32 (0.1) | 11 (0.05) | 7 (0.2) | 1 (0.2) | |
| Maternal death | 2 (0.01) | 1 (0.00) | 1 (0.03) | 0 | |
| Unexpected procedure | 154 (0.6) | 129 (0.6) | 27 (0.7) | 6 (1.0) |
Abbreviations: BMI, body mass index; DIC, disseminated intravascular coagulation; DVT, deep venous thrombosis; ICU, intensive care unit; PE, pulmonary embolus.
Note: Missing: hemorrhage (2), sepsis (1), DIC (1), DVT/PE (1), stroke (1), ICU (1), ventilator use (1), maternal death (1).
Cochran–Armitage test for trend.
Multivariable Poisson’s regression following assignment of a propensity score revealed that after controlling for preeclampsia and chronic hypertension, BMI was significantly associated with the composite of serious morbidity and mortality only in the SMO group (OB: aRR = 1.06, 95% CI: 0.99–1.14; MO: aRR = 1.10, 95% CI: 0.97–1.25; SMO: aRR = 1.32, 95% CI: 1.02–1.70; Table 4).
Table 4.
Models of maternal composite outcome and components by BMI category at delivery
| Reference (REF) | Obese (OB) | Morbidly obese (MO) | Super morbidly obese (SMO) | |
|---|---|---|---|---|
| n = 26,081 | n = 21,704 | n = 3,787 | n = 590 | |
| Unadj RR (95% CI) | 1.00 (referent) | 1.10 (1.02–1.18) | 1.26 (1.11–1.43) | 1.60 (1.23–2.09) |
| Model 1 aRR (95% CI)a | 1.00 (referent) | 1.06 (0.99–1.14) | 1.10 (0.97–1.25) | 1.32 (1.02–1.70) |
| Model 2 aRR (95% CI) b | 1.00 (referent) | 1.03 (0.96–1.11) | 1.02 (0.90–1.16) | 1.17 (0.90–1.52) |
Abbreviations: aRR, adjusted relative risk; BMI, body mass index; CI, confidence interval; Unadj., unadjusted.
Model 1 adjusted for chronic hypertension and preeclampsia.
Model 2 adjusted for chronic hypertension, preeclampsia and mode of delivery.
The association between SMO and the composite outcome was lost when mode of delivery was added to the adjusted model (OB: aRR = 1.03, 95% CI: 0.96–1.11; MO: aRR = 1.02, 95% CI: 0.90–1.16; SMO: aRR = 1.17, 95% CI: 0.90–1.52; Table 4) In the mediation analysis, cesarean appears to mediate 46% (95% CI: 31–50%) of the risk of severe morbidity for SMO compared with REF.
Discussion
Our study expands on prior reports that have suggested that maternal complications are increased in obese gravidas by including a very large multicenter cohort of women with singleton pregnancies, including almost 600 with SMO (BMI ≥ 50 kg/m2).11–21 As a result, while most prior studies report outcomes for all obese women (BMI ≥ 30 kg/m2) as a single group, we are able to describe an increasing rate of maternal complications with progressive increases in BMI. Fortunately, serious morbidities are uncommon, and it requires a large database such as this to detect differences in different BMI populations. After controlling for confounding factors, the composite outcome of serious maternal morbidity was increased only in the SMO group. However, even this association was lost when mode of delivery was added to the analysis.
Other authors have reported finding increased pregnancy complications in obese populations. Kim et al compared women with a BMI of ≥ 60 kg/m2 (n = 39) to a randomly selected sample of those with a BMI of 30–39 kg/m2 (n = 100), a BMI of 40–49 kg/m2 (n = 100), and a BMI of 50–59 kg/m2 (n = 99) and reported increased rates of labor induction, cesarean delivery, wound complications, postpartum hemorrhage and hospital stay >5 days.22 After excluding fetal anomalies and women with hypertension or diabetes, Marshall and colleagues compared women with OB (n = 53,032), MO (n = 10,055), and SMO (n = 1,185).25 They found that comparing SMO to OB, the RR for preeclampsia was 1.7 and for cesarean delivery was 1.8; the RR was 1.4 for both in comparing MO to OB. Mantakas and Farrell also noted that the rates of cesarean delivery, macrosomia, and stillbirth incrementally increased with increasing BMI, such that MO women (BMI > 40 kg/m2) had a 2.2-fold increase in cesarean delivery, a 3.1-fold increase in macrosomia, and 16.7-fold increase in stillbirth.26
Although not evaluated in the multivariable analysis, in the univariate analysis, similar to others, we found that maternal obesity increases the risk for labor induction and failed induction, failed trial of labor following a prior cesarean delivery, and for cesarean delivery. We also confirmed the increased risk for preeclampsia, preterm delivery, and infectious complications, including suspected chorioamnionitis and endometritis. We were also able to demonstrate an increased risk for malpresentation and amniotic fluid abnormalities at delivery.
The contribution of cesarean delivery only to the morbidity experienced by SMO women is an intriguing finding of this study. Many of the components of the composite outcome are seen following cesarean delivery but are not necessarily limited to operative deliveries. Although the role of cesarean delivery in maternal morbidity in OB women remains unclear, it would appear that lowering the cesarean rate in women who are SMO would be of benefit in reducing serious morbidity in these women. Leonard and colleagues also found that cesarean delivery, but not obesity, (prepregnancy BMI ≥ 30 kg/m2) contributed to severe maternal morbidity.27 Prepregnancy risk factors also contributed but not advanced maternal age.
Strengths and Limitations
The strengths of our study include the large number of women included in the analysis, particularly those with a BMI of ≥ 50 kg/m2. This allowed the evaluation of less common pregnancy complications in the obese pregnant woman. The population studied also represents a varied sample from several different geographical settings across the United States. The database used was created by trained abstractors with performance of frequent data quality checks.
The major weakness of this study is its retrospective nature, such that some questions cannot be answered by the database. Thus, our study cannot address additional obstetric complications of obesity, such as subfertility and higher rates of early pregnancy loss.28 In addition, we cannot address either the nature or the frequency of postdelivery discharge complications. In addition, a majority (22/25) of the hospitals that participated in the study are teaching hospitals, potentially limiting the generalizability of our findings. Importantly, prepregnancy weight was not initially recorded in the database and thus is missing in over half of the population. As a result, the effect of weight gain could not be evaluated.
Conclusion
Our study highlights the increasing rates of serious morbidity seen with increasing BMI and also emphasizes the importance of weight loss prior to conception, controlling weight gain during the pregnancy, as well as reducing cesarean delivery rates. The correlation between obesity and poor pregnancy outcomes does not prove causation, however. Further studies are needed to assess the interactions between BMI, cesarean delivery, and serious maternal morbidity. The results of this study will be valuable to clinicians counseling women with obesity, both prior to conception, as well as during pregnancy. It confirms prior studies that suggest poorer pregnancy outcomes in women with an increased BMI and attempts to quantify those risks. Continued efforts to reduce obesity, the rate of primary cesarean delivery, as well as the morbidity associated with cesarean delivery in the obese population, remain paramount.
Supplementary Material
Key Points.
Super morbid obesity is associated with increased morbidity.
Cesarean appears to mediate the association between super morbid obesity and morbidity.
Obesity and morbid maternal obesity are not associated with morbidity.
Acknowledgments
The authors thank William A. Grobman, MD, MBA, Elizabeth Thom, PhD, Madeline M. Rice, PhD, Brian M. Mercer, MD, and Catherine Y. Spong, MD for protocol development and oversight.
Funding
The project described was supported by grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD; grant numbers: HD21410, HD27869, HD27915, HD27917, HD34116, HD34208, U10 HD36801, HD40500, HD40512, HD40544, HD40545, HD40560, HD40485, HD53097, and HD53118) and the National Center for Research Resources (grant numbers: UL1 RR024989 and 5UL1 RR025764). Comments and views of the authors do not necessarily represent views of the National Institutes of Health.
Footnotes
Conflict of interest
None declared.
Presented in part at the 38th annual meeting of the Society for Maternal-Fetal Medicine, January 29-February 3, 2018, Dallas, TX.
References
- 1.May AL, Freedman D, Sherry B, Blanck HM, Centers for Disease Control and Prevention (CDC) Obesity - United States, 1999–2010. MMWR Suppl 2013;62(03):120–128 [PubMed] [Google Scholar]
- 2.Freedman DS, Centers for Disease Control and Prevention (CDC) Obesity - United States, 1988–2008. MMWR Suppl 2011;60(01): 73–77 [PubMed] [Google Scholar]
- 3.Ogden CL, Carroll MD, Kit BK, Flegal KM. Prevalence of childhood and adult obesity in the United States, 2011–2012. JAMA 2014; 311(08):806–814 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Flegal KM, Carroll MD, Kit BK, Ogden CL. Prevalence of obesity and trends in the distribution of body mass index among US adults, 1999–2010. JAMA 2012;307(05):491–497 [DOI] [PubMed] [Google Scholar]
- 5.WHO. BMI Data. Accessed February 19, 2019 at: https://www.who.int/data/gho/data/themes/topics/topic-details/GHO/body-mass-index
- 6.Palmer MK, Toth PP. Trends in lipids, obesity, metabolic syndrome, and diabetes mellitus in the United States: An NHANES analysis (2003–2004 to 2013–2014). Obesity (Silver Spring) 2019;27(02): 309–314 [DOI] [PubMed] [Google Scholar]
- 7.Martin JA, Hamilton BE, Osterman MJK, Driscoll AK. Births: final data for 2018. Natl Vital Stat Rep 2019;68(13):1–47 [PubMed] [Google Scholar]
- 8.Singh GK, DiBari JN. Marked disparities in pre-pregnancy obesity and overweight prevalence among US women by race/ethnicity, nativity/immigrant status, and sociodemographic characteristics, 2012–2014. J Obes 2019;2019:241–263 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.March of Dimes. Obesity among women of childbearing age: United States, 2010–2020. Accessed August 1, 2020 at: https://www.marchofdimes.org/peristats/data?top=17&lev=1&stop=350®=99&obj=1&slev=1
- 10.Downs DS. Obesity in special populations. Prim Care 2016;43(01):109–120 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Weiss JL, Malone FD, Emig D, et al. ; FASTER Research Consortium. Obesity, obstetric complications and cesarean delivery rate–a population-based screening study. Am J Obstet Gynecol 2004;190(04):1091–1097 [DOI] [PubMed] [Google Scholar]
- 12.Lim CC, Mahmood T. Obesity in pregnancy. Best Pract Res Clin Obstet Gynaecol 2015;29(03):309–319 [DOI] [PubMed] [Google Scholar]
- 13.Wolfe KB, Rossi RA, Warshak CR. The effect of maternal obesity on the rate of failed induction of labor. Am J Obstet Gynecol 2011;205(02):128.e1–128.e7 [DOI] [PubMed] [Google Scholar]
- 14.Marchi J, Berg M, Dencker A, Olander EK, Begley C. Risks associated with obesity in pregnancy, for the mother and baby: a systematic review of reviews. Obes Rev 2015;16(08):621–638 [DOI] [PubMed] [Google Scholar]
- 15.Mission JF, Marshall NE, Caughey AB. Obesity in pregnancy: a big problem and getting bigger. Obstet Gynecol Surv 2013;68(05):389–399 [DOI] [PubMed] [Google Scholar]
- 16.Sebire NJ, Jolly M, Harris JP, et al. Maternal obesity and pregnancy outcome: a study of 287,213 pregnancies in London. Int J Obes Relat Metab Disord 2001;25(08):1175–1182 [DOI] [PubMed] [Google Scholar]
- 17.Lashen H, Fear K, Sturdee DW. Obesity is associated with increased risk of first trimester and recurrent miscarriage: matched case-control study. Hum Reprod 2004;19(07):1644–1646 [DOI] [PubMed] [Google Scholar]
- 18.Torloni MR, Betrán AP, Horta BL, et al. Prepregnancy BMI and the risk of gestational diabetes: a systematic review of the literature with meta-analysis. Obes Rev 2009;10(02):194–203 [DOI] [PubMed] [Google Scholar]
- 19.Stothard KJ, Tennant PWG, Bell R, Rankin J. Maternal overweight and obesity and the risk of congenital anomalies: a systematic review and meta-analysis. JAMA 2009;301(06):636–650 [DOI] [PubMed] [Google Scholar]
- 20.Korkmaz L, Baştuğ O, Kurtoğlu S. Maternal obesity and its short-and long-term maternal and infantile effects. J Clin Res Pediatr Endocrinol 2016;8(02):114–124 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Fyfe EM, Anderson NH, North RA, et al. ; Screening for Pregnancy Endpoints (SCOPE) Consortium. Risk of first-stage and second-stage cesarean delivery by maternal body mass index among nulliparous women in labor at term. Obstet Gynecol 2011;117(06):1315–1322 [DOI] [PubMed] [Google Scholar]
- 22.Kim T, Burn SC, Bangdiwala A, Pace S, Rauk P. Neonatal morbidity and maternal complication rates in women with a delivery body mass index of 60 or higher. Obstet Gynecol 2017;130(05):988–993 [DOI] [PubMed] [Google Scholar]
- 23.Bailit JL, Grobman WA, Rice MM, et al. ; Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal–Fetal Medicine Units Network. Risk-adjusted models for adverse obstetric outcomes and variation in risk-adjusted outcomes across hospitals. Am J Obstet Gynecol 2013;209(05):446.e1–446.e30 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Grobman WA, Bailit JL, Rice MM, et al. ; Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Can differences in obstetric outcomes be explained by differences in the care provided? The MFMU Network APEX study. Am J Obstet Gynecol 2014;211(02):147.e1–147.e16 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Marshall NE, Guild C, Cheng YW, Caughey AB, Halloran DR. Maternal superobesity and perinatal outcomes. Am J Obstet Gynecol 2012;206(05):417.e1–417.e6 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26.Mantakas A, Farrell T. The influence of increasing BMI in nulliparous women on pregnancy outcome. Eur J Obstet Gynecol Reprod Biol 2010;153(01):43–46 [DOI] [PubMed] [Google Scholar]
- 27.Leonard SA, Main EK, Carmichael SL. The contribution of maternal characteristics and cesarean delivery to an increasing trend of severe maternal morbidity. BMC Pregnancy Childbirth 2019;19(01):16–24 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Klenov VE, Jungheim ES. Obesity and reproductive function: a review of the evidence. Curr Opin Obstet Gynecol 2014;26(06):455–460 [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.