standardizing longitudinal data-which order?

#1
My PI suggested I standardize values for a longitudinal dataset we are looking at. There are 4 time points, (one time point during pregnancy, and three time points after) and we are trying to control for the pregnancy scores of a variable.
Therefore, we are using a stacked variable that repeats itself 4 times(the value of the first time point) and then including that in the model with the other variable that has four different values representing the four different time points. (This is in a long format)

So my PI has suggested I standardize the values. I am not sure as to what step I should standardize them, because if I do it once I have my long dataset, I will be standardizing each value using the mean of ALL visits. Would it be accurate to do this and then for the "first" variable, only standardize that across the "first" visits? To me it seems odd because if I chose to do it the other way and standardize all the values across four visits and then pull the "first" that would be a different value.

I'm not sure which order is better. Thank you!