"knock up" --usage

[Mullins, Bill]

>
> Just within the last two nights I heard Peter Bagdonovich on
> Turner Classic Movies mention very casually that some
> celebrated actress of the forties or fifties had done
> something or other (obviously I wasn't paying much attention)
> while she was "knocked up."
>
> I thought this was pretty crude for a classy cinematic
> discussion in prime time (even on cable), but evidently
> neither P.B. nor the TCM people shared my puritanical response.
>
> After all, it's just "knocked" + "up."  Where's the dirt ?  (Goak.)
>


Is this phrase related beyond coincidence to "knock boots" = have sex?