Background: Women with multiple sclerosis (MS) who become pregnant and utilize maternity services may find their use of disease-modifying therapies (DMT) impacted for a number of reasons. Objectives: To investigate the impacts of that life change upon adherence to DMT medications, healthcare utilization, and healthcare costs; and, identify significant associations between DMT adherences among women utilizing maternity services in regards to comorbidities, healthcare cost and utilization over a 2-year period. Methods: A retrospective cohort design with commercially-insured patients from the MarketScan Commercial Claims and Encounters database from 2015–2017. DMT adherence was calculated with Pharmacy Quality Alliance (PQA) proportion of days (PDC) criteria. Selected patients had at least two DMT fills starting 1/1/2015 (with 2-year follow-up through 12/2017 from index), and no indication of death or hospice stay. MS diagnosed females were categorized as pregnant in the first year or second year, and as consistently adherent (PDC ? 80%) in either years, adherent only in one year, or adherent in neither year. Outcomes were combined 2-year total adjusted medical costs (inpatient and outpatient less maternity services), DMT pharmacy costs, and associated MS medication costs. Model covariates included age, initial maternity year, census region, metropolitan location, presence of comorbidity, associated MS medication therapy group counts, DMT switching, mail order, and changed insurance type. Results: Of pregnancies utilizing maternity services, 82.7% (500/604) were in the first year follow-up period. Of the 500 first-year pregnancies, 79% discontinued DMT utilization into their second year. Analysis on 603 patients DMT utilization found 9.2% adherent in both years, 39.9% adherent in one year and 53.9% were non-adherent in both years. Adjusted costs for DMT pharmacy prescriptions were significantly higher for those consistently adherent vs never adherent (a 2.6 multiple). Patients who were consistently adherent had significantly lower adjusted medical costs compared to those consistently non-adherent (-$4,383, p<.002) or to those with mixed adherence (-$2.951, p<.04). Conclusions: MS patients in maternity typically reduce their DMT medication adherence; however, a significant number continue, even at a good adherence level (PDC ?.80). Mean non-maternity medical costs for adherent patients was significantly lower compared to other two DMT non-adherent or discontinued patient groups.