Blatantly regressive concealing of birth (5)
I believe the answer is:
natal
'of birth' is the definition.
(natal means relating to birth)
'blatantly regressive concealing' is the wordplay.
'concealing' indicates the answer is hidden within the clue.
'regressive' says the letters should be written backwards (to regress is to go backwards).
'latan' is hidden within 'blatantly'.
'latan' back-to-front is 'NATAL'.
(Other definitions for natal that I've seen before include "Native" , "Colony once" , "Relating to deliveries" , "Relating to birth - former South African province" , "Concerned with the birth" .)