Gestational diabetes mellitus (GDM) increases the risk of adverse outcomes during and after pregnancy, including a long-term risk of type 2 diabetes. Women with GDM are treated by numerous healthcare professionals during pregnancy and describe a lack of preventive care after pregnancy. We aim to investigate healthcare professionals' perspectives on the cross-sectoral treatment pathway for women with GDM-during and after pregnancy. A qualitative study was conducted using systematic text condensation. Nine healthcare professionals (two general practitioners, four midwives, two obstetricians and one diabetes nurse) were interviewed and eight health visitors participated in two focus group discussions., Three major themes emerged: (1) "professional identities", which were identified across healthcare professionals and shaped care practices; (2) "unclear guidelines on type 2 diabetes prevention after GDM", which contributed to uncertainty about tasks and responsibilities during and after pregnancy; and (3) "cross-sectoral collaboration", which relied heavily on knowledge transfers between hospitals, general practice and the local municipality. The findings implicate that clear, transparent guidelines for all sectors should be prioritized to strengthen cross-sectoral care to women with GDM during and after pregnancy. As a result, strong cross-sectoral care throughout the GDM care pathway may improve maternal health by supporting healthy behaviors, facilitate weight loss and reduce the risk of subsequent GDM and early onset diabetes.