In general, use periods in academic degrees:
The exception is MBA. Most reference books, including the dictionary, leave the periods out of that one, so we will, too.
In BHG magazine, use periods in professional certifications:
C.D.C.E.S. (formerly C.D.E.; updated 7/31/20)
In SIM content, on the other hand, do not use periods in professional certifications:
CDCES (formerly CDE; updated 7/31/20)
Sometimes this will result in mixed formats in a single byline:
Jane Johnson, Ph.D., CDE