O21 ICD-10-CM Code: Excessive vomiting in pregnancy

O21 is the ICD-10-CM diagnosis code for excessive vomiting in pregnancy. O21 sits in the ICD-10-CM chapter for pregnancy, childbirth and the puerperium (o00-o9a), within the section covering other maternal disorders predominantly related to pregnancy (o20-o29).

Header codes like O21 cannot be reported on claims directly, they organize child codes that share clinical context but the actual diagnosis must be coded to the highest level of specificity supported by the documentation. Coders should look at O21's child codes and select the one that matches the patient's documented presentation, since payers reject header codes submitted as the primary diagnosis. For risk adjustment workflows, header codes never contribute to a Medicare Advantage member's RAF score on their own; only billable child codes that happen to map to a payment HCC affect risk-adjusted plan payments.