It is advisable to discuss your ATSM plans at your ST4 ARCP or following passing your part 3 of MRCOG. To register you need to complete the RCoG ATSM registration form. Further information on the application process and the registration fees can be found here: https://www.rcog.org.uk/en/careers-training/specialty-training-curriculum/atsms/introduction/how-to-register-for-an-atsm/. Registration cannot take place before the start of ST6.