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

The purpose of this study was to determine the effect of body mass index category on pregnancy outcomes.

Five databases (Medline, Embase, PubMed, www.clinicaltrials.gov, and Cochrane) were searched from inception until February 2019 for English or French publications that reported on pregnancy outcomes in women with body mass index ≥30 kg/m². Reference lists of included articles were searched, and authors were contacted for missing data where necessary. Because no randomized trials were identified, we included single-center and population-based cohort studies that stratified pregnancy outcomes under the following body mass index categories: underweight, standard weight, overweight, and obese classes I-III, based on the World Health Organization international classification system.

Study quality was appraised with the use of the Newcastle-Ottawa Scale Quality Assessment Scale for cohort studies. Because significant heterogeneity was anticipated among studies, we used random-effects metaanalysis to arrive at pooled estimates and 95% confidence intervals for pregnancy outcomes in each body mass index category and relative risks in relation to women with a standard body mass index.

We identified 10,258 studies, of which 13 studies with a low risk-of-bias that described 3,722,477 pregnancies that were included in the metaanalysis. Most adverse pregnancy outcomes increased steadily with increasing body mass index category. Compared with women with body mass index 18.5-24.9 kg/m², women with body mass index >40 kg/m² were at increased risk for gestational diabetes mellitus [17% vs 3.9%; relative risk, 4.6 [95% confidence interval, 3.6-5.9]), hypertensive disorders of pregnancy (15.9% vs 3.5%; relative risk, 4.6 [95% confidence interval, 3.4-6.0]), and cesarean delivery (47.7% vs 26.0%; relative risk, 1.86 [95% confidence interval, 1.75-1.97]). Babies were at increased risk for hypoglycemia (4.1% vs 1.4%; relative risk, 3.3 [95% confidence interval, 2.8-3.8]), macrosomia (12.9% vs 6.2%; relative risk, 2.6 [95% confidence interval, 1.4-4.7]), infection (2.8% vs 1.3%; relative risk, 2.3 [95% confidence interval, 1.6-3.3]), birth trauma (1.3% vs 0.9%; relative risk, 2.1 [95% confidence interval, 1.2-3.8]), respiratory distress (5.1% vs 2.7%; relative risk, 2.0 [95% confidence interval, 1.8-2.2]), death (1.4% vs 0.9%; relative risk, 1.8 [95% confidence interval, 1.2-2.9]), and neonatal intensive care unit admission (13.5% vs 9.5%; relative risk, 1.6 [95% confidence interval, 1.4-1.9]).

There is a linear association between maternal body mass index and almost all adverse pregnancy outcomes. These risks, stratified by body mass index category as presented in this article, would facilitate counselling and encourage appropriate interventions to improve outcomes for mothers and babies.