LAUSR

BACKGROUND Surveillance of maternal mortality and severe maternal morbidity (SMM) is important to identify temporal trends, evaluate the impact of clinical practice changes or interventions, and to monitor quality of care. A common source for SMM surveillance is hospital discharge data. On October 1, 2015 all hospitals in the United States transitioned from International Classification of Disease Version 9 Clinical Modification (ICD-9-CM) to International Classification of Disease Version 10 Clinical Modification (ICD-10-CM) coding for diagnoses and procedures. OBJECTIVE This study aimed to evaluate the impact of the transition between ICD-9-CM to ICD-10-CM coding systems on the incidence of SMM in the United States in hospital discharge data. STUDY DESIGN Using data from the National Inpatient Sample, obstetric deliveries between January 1 2012 and December 31 2017 were identified using a validated case definition. SMM was defined using ICD-9-CM (January 1 2012-September 30 2015) and ICD-10-CM (October 1 2015-December 31 2017) codes provided by the Centers for Disease Control. An interrupted time series and segmented regression analysis was used to assess the impact of the transition between ICD-9-CM and ICD-10-CM coding on the incidence of SMM per 1000 obstetric deliveries. RESULTS From 20,377,341 deliveries, the incidence of SMM in the ICD-9-CM coding era was 79.2 per 1000 obstetric deliveries and decreased to 24.7 per 1000 obstetric deliveries in the ICD-10-CM coding era (p<0.001). The transition to ICD-10-CM coding lead to an immediate decrease in the incidence of SMM (-59.8 cases/1000 obstetric deliveries) and a reversal of the temporal trend, from a monthly increase of 0.2 cases/1000 obstetrics deliveries per month in the ICD-9-CM coding era to a decrease of 0.2 cases/1000 obstetrics deliveries per month (relative to the initial trend) in the ICD-10-CM coding era. CONCLUSIONS Following the transition to ICD-10-CM coding for health diagnoses and procedures in the United States, there was an abrupt statistically significant and clinically meaningful decrease in the incidence of SMM in hospital discharge data. Changes in the underlying health of the obstetric population are unlikely to explain the sudden change in SMM. While much work has been done to validate ICD-9-CM codes for SMM, it is critical that validation studies be undertaken to validate ICD-10-CM codes for SMM to permit ongoing surveillance, quality improvement, and research activities that rely on hospital discharge data.