Condition when expecting girl to follow quiet short boy (9)

'condition' is the definition.
(I know that pregnancy is a type of physical condition)

'expecting girl to follow quiet short boy' is the wordplay.
I cannot really understand how this works, but
'girl' could be 'nancy' and 'nancy' is found in the answer.
'quiet' could be 'p' (music symbol for 'piano', ie soft or quiet) and 'p' is found in the answer.
'boy' could be 'reg' and 'reg' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).

'when' acts as a link.

Can you help me to learn more?