Not necesarily a sign of impending motherhood.
How often do you do partial water changes? The racing up and down could be them trying to escape from something nasty in the water. In my experiance a soon to deliver female will race up and down. But only when in full labor and the fry are partially visible.
When all else fails and you don't know what to do...do a 25% water change with seasoned (if possible) treated water. That will get rid of a bit of nasty stuff and can even trigger close to dropping females to have their fry.
Before all else fails....do a 25% water change ;)
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