another condition whenever the cell is blank

I'm having trouble with my project. I want to compute their weight status but I have 4 weight records.

I have this problem that I wanna solve:

if the 4th weight is blank then it will directly go to the 3rd weight same here if the 3rd is blank it will go to the 2nd and so on. 

Here is the code for my prediction

here is my data where I compare my prediction