Maternal body mass index and pregnancy outcomes: a systematic review and metaanalysis

Abstract

T he global prevalence of obesity (body mass index [BMI], 30 kg/m 2 ) has tripled since 1975, and it is estimated that, in 2016, >1.9 billion adults were overweight (BMI, 25e29.9 kg/m 2 ), of which >650 million adults were obese. 1 Among women giving birth in the United States in 2014, 50.4% were either overweight or obese. 2 In addition, adults with a BMI of kg/m 2 comprise the most rapidly growing class of obesity in the United States. 3 Pregnant women who are classified as overweight or obese are known to be at increased risk for adverse maternal and fetal/neonatal outcomes. 4,5 However, the increased risk of pregnancy complications with each obesity class over that for women with standard BMI has not been assessed systematically. Given the high prevalence of obesity among women of childbearing age, the importance of estimating pregnancy risk with increasing BMI categories has become more pertinent than ever. ObjectiveThe objective of this study was to metaanalyze data that compares pregnancy outcomes in women with obesity and that are stratified by obesity class, with the view to counselling women and informing preventative strategies preconceptionally and during pregnancy. MethodsThis study was conducted as part of study to scrutinize the effect of obesity on mode of delivery; the study protocol

Birth outcomes in women with body mass index of 40 kg/m2 or greater stratified by planned and actual mode of birth: a systematic review and meta‐analysis

“…The protocol has been registered with PROSPERO (CRD42017074290). This protocol covered two distinct systematic reviews – the first looking at the incidence of complications stratified by increasing BMI, the findings of which have been published separately, 2 and the second, which is the focus of this manuscript. This review was conducted and reported according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) and meta‐analysis of observational studies in epidemiology (MOOSE) guidelines respectively 8,9 …”

“…While women with BMI 30‐39.9 kg/m 2 seldom pose a clinical dilemma with regard to determining the mode of birth, those with a BMI ≥ 40 kg/m 2 are at increased risk for complications during childbirth. A recent systematic review comparing pre‐existing medical conditions and pregnancy outcomes stratified by BMI, showed that when compared with pregnant women with BMI 18.5‐24.9 kg/m 2 (n = 1 905 339), those with BMI ≥ 40 kg/m 2 (n = 82 691) are at increased risk for entering pregnancy with pre‐existing diabetes (4.14% vs 0.71%, relative risk (RR) 6.58) and essential hypertension (8.86% vs 0.69%, RR 12.37), and also of developing gestational diabetes (17.01% vs 3.85%, RR 4.62) and hypertensive disorders during pregnancy (15.86% vs 3.46%, RR 4.55) 2 . These conditions, as well as other factors such as a poor response to labor induction 3 and augmentation, 3 protracted labor courses, 4 and fetal macrosomia (12.86% vs 6.18%, RR 2.55), 2 result in a higher rate of planned‐ (29.81% vs 17.33%, RR 1.67) and unplanned (21.72% vs 13.92%, RR 1.53) cesarean delivery (CD), 2 and an associated increase in wound complications 5 .…”

“…A recent systematic review comparing pre‐existing medical conditions and pregnancy outcomes stratified by BMI, showed that when compared with pregnant women with BMI 18.5‐24.9 kg/m 2 (n = 1 905 339), those with BMI ≥ 40 kg/m 2 (n = 82 691) are at increased risk for entering pregnancy with pre‐existing diabetes (4.14% vs 0.71%, relative risk (RR) 6.58) and essential hypertension (8.86% vs 0.69%, RR 12.37), and also of developing gestational diabetes (17.01% vs 3.85%, RR 4.62) and hypertensive disorders during pregnancy (15.86% vs 3.46%, RR 4.55) 2 . These conditions, as well as other factors such as a poor response to labor induction 3 and augmentation, 3 protracted labor courses, 4 and fetal macrosomia (12.86% vs 6.18%, RR 2.55), 2 result in a higher rate of planned‐ (29.81% vs 17.33%, RR 1.67) and unplanned (21.72% vs 13.92%, RR 1.53) cesarean delivery (CD), 2 and an associated increase in wound complications 5 . These pregnancies are also at risk for neonatal complications that could be, directly or indirectly, related to the labor and birth, such as birth trauma (1.26% vs 0.88%, RR 2.07), neonatal hypoglycemia (4.05% vs 1.38%, RR 3.27), early neonatal infection (2.75% vs 1.34%, RR 2.25), respiratory distress (5.08% vs 2.74%, RR 1.98), neonatal intensive care unit admissions (13.74% vs 9.51%, RR 1.63) and neonatal death (1.42% vs 0.93, RR 1.84) 2 .…”

“…These conditions, as well as other factors such as a poor response to labor induction 3 and augmentation, 3 protracted labor courses, 4 and fetal macrosomia (12.86% vs 6.18%, RR 2.55), 2 result in a higher rate of planned‐ (29.81% vs 17.33%, RR 1.67) and unplanned (21.72% vs 13.92%, RR 1.53) cesarean delivery (CD), 2 and an associated increase in wound complications 5 . These pregnancies are also at risk for neonatal complications that could be, directly or indirectly, related to the labor and birth, such as birth trauma (1.26% vs 0.88%, RR 2.07), neonatal hypoglycemia (4.05% vs 1.38%, RR 3.27), early neonatal infection (2.75% vs 1.34%, RR 2.25), respiratory distress (5.08% vs 2.74%, RR 1.98), neonatal intensive care unit admissions (13.74% vs 9.51%, RR 1.63) and neonatal death (1.42% vs 0.93, RR 1.84) 2 . While it is generally accepted that a vaginal birth is preferred over a CD, the challenges with induction and surveillance of labor, and the high possibility of requiring a technically‐challenging unplanned CD, 6 and subsequently, sub‐optimal outcomes, 7 in women with BMI ≥ 40 kg/m 2 , raises the question on the optimal method of delivery in these women.…”

Variation in outcome reporting in studies on obesity in pregnancy—A systematic review

“…It is well established that women with obesity are at increased risk for adverse pregnancy outcomes and that their children are at risk for childhood obesity, as well as metabolic disease in later life . Published and ongoing clinical trials explore interventions to improve outcomes for these women and children.…”