Previous studies show that obesity predisposes patients to higher risks of adverse pregnancy outcomes. Data on the relationship between increasing degrees of obesity and risks of severe maternal morbidity (SMM), including mortality, are limited.
We examined the association of increasing classes of obesity, especially super obesity, with the risk of SMM and mortality at the time of delivery hospitalization.
Using New York City linked birth certificates and hospital discharge data we conducted a retrospective cohort study. This study identified delivery hospitalizations for singleton, live births in 2008-2012. Women were classified as having obesity (Class I, II, III or super obesity), as opposed to normal weight or overweight, based on pre-pregnancy body mass index (BMI). Cases of SMM were identified based on International Classification of Diseases -9 (ICD-9) diagnosis and procedure codes according to Centers for Disease Control and Prevention (CDC) criteria. Multivariable logistic regression was used to evaluate the association between obesity classes and SMM, adjusting for maternal socio-demographic characteristics.
During 2008-2012, there were 570,997 live singleton births with available information on pre-pregnancy BMI who met all inclusion criteria. After adjusting for maternal characteristics, women with Class II (aOR 1.14, 95% CI 1.05-1.23), Class III (aOR 1.34, 95% CI 1.21-1.49), and super obesity (aOR 1.99, 95% CI 1.57-2.54) were all significantly more likely to have SMM compared to normal and overweight women. Super obesity was associated with specific SMM indicators including: renal failure, air and thrombotic embolism, blood transfusion, heart failure, and the need for mechanical ventilation.
There is a significant dose-response relationship between increasing obesity class and the risk of SMM at delivery hospitalization. The risks of SMM are highest for women with super obesity. Given that this is a modifiable risk factor, women with pre-pregnancy obesity should be counseled on the specific risks associated with pregnancy prior to conception in order to optimize their pregnancy outcomes.

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