By default, Word suppresses blank lines where
a. there is at least one MERGEFIELD field on the line
b. everything on the line evaluates to an empty string (i.e., there are no
spaces, tabs, etc.)

So I'd look for things that generate anything except an empty string...

However, in Word 2002/3, if the MERGEFIELDs are nested inside another field,
Word does not suppress blank lines and you will have to use IF fields to
suppress them.

Peter Jamieson