In simple terms, you can move the data into a table specifically configured for export. You can name the fields in this table as needed to get your column headings and combine data from different records (rows) into a single row where each record populates a different column.
I would guess that there are also ways to do this with an XML report by setting up the appropriate XSLT grammar.
In order to do the "simple", I'd have to categories my follow-ups within the Measurement table though, correct? Otherwise, I suppose I could put the categorization rules in the field definition of the new table...
It seems you are basing your data on the time between checkups.
You could add a field for date of last visit to your record and then determine the number of weeks based on
current date - previous date / 7 or something similar. Now each record would have the week number you are looking for.
You can find and sort the patients record by date and start with the first record and capture its date and go to the second record and paste. Capture the date of the second and go to the third, etc.
Does this sound like what you need?
Actually, it's from the time of their first treatment. We just can't pin people down to come in at _exactly_ 3 months (for example), so it can be off by 4 weeks on either side.