Year on Year Percent - excluding from total if no previous year value available

[catmoore]

Hi

I am trying to amend a Year on Year calculation to ignore current period values when no value exists for the previous period. 

Can this be achieved via DAX?

My current measure is as below:

YoY = 1-TOTALQTD(sum(Table[Measure]),PARALLELPERIOD(Months[QuarterDate],-4,quarter))/(TOTALQTD(sum(Table[Measure]),Months[QuarterDate]))