Submission Type

Original Research


Introduction: Incidence rates of neonatal abstinence syndrome (NAS) have increased in Maine, but whether this increase can be explained by use of different diagnosis codes over time is unknown. Our objective was to estimate trends in diagnoses of NAS at newborn hospitalization in Maine using different NAS case definitions.

Methods: We used International Classification of Diseases (ICD) diagnosis codes to identify newborns diagnosed with NAS in Maine between 2009 and 2018 using state-level hospital discharge data (n = 123 519). First, we considered only ICD-9 and ICD-10 codes used for confirmed NAS. Then we used an expanded ICD-10 NAS case definition that included codes for neonates suspected to have NAS and affected by an unspecified “other maternal medication.” We used joinpoint regression to model trends over time and identified changes in slope.

Results: Using the case definition for confirmed NAS, diagnoses of NAS increased from 2009 to 2013 (from 20 to 38 per 1000 births), and then decreased from 2013 to 2018 (from 38 to 28 per 1000 births). Using our expanded ICD-10 NAS case definition, NAS increased linearly from 2009 to 2018 (from 24 to 50 per 1000 births).

Discussion: The trends in diagnoses of NAS were different when based on the expanded or confirmed NAS case definition.

Conclusions: Validation studies are needed to understand which infants are coded using the expanded versus confirmed NAS case definition. Caution should be used when interpreting rates of NAS in Maine using hospital discharge data.



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