Most studies consider either medications ordered or filled, but not both. Medication underuse based on filling data cannot necessarily be ascribed to patient nonadherence. Using both data sources, we quantified primary medication adherence in a cohort of prevalent systemic lupus erythematosus (SLE) pregnancies. We identified 419 pregnancies in Kaiser Permanente Northern California in patients with prevalent SLE from 2011 to 2020. We calculated the number of physician-initiated orders or pharmacy-initiated reorders during pregnancy and a comparable 9-month window the year before (prepregnancy) and the proportion of orders ever filled and filled within 30 days for hydroxychloroquine (HCQ), azathioprine, and corticosteroids. For pregnancies without an order or reorder, we identified the proportion with previous prescription fills overlapping into the respective study period. New orders for lupus medications were usually filled. HCQ was prescribed most often (45.8% pregnancies) and usually filled (89.7% in prepregnancy, 93.2% during pregnancy). The majority filled within 30 days (80.5% prepregnancy, 83.3% pregnancy). Some pregnancies without new HCQ orders had continuous refills from prior orders; 53% of 2011-2015 pregnancies either had a new order or fill coverage from a previous period, compared to 63.2% of pregnancies delivering in 2016-2019. Corticosteroid fill frequencies were 90.6% in prepregnancy and 83.6% during pregnancy. Fewer patients used azathioprine; however, most new orders were filled (94.3% prepregnancy, 91.7% pregnancy). For azathioprine and corticosteroids, fill rates were modestly higher in prepregnancy compared to pregnancy. We observed that patients have high adherence to filling new orders for lupus medications, such as HCQ and azathioprine, in pregnancy.