I didn't see the original post but I feel that I need to offer my experience.
My eldest is 20 and when I was 31 weeks pregnant with him I traveled on a really bad dirt road with potholes, etc. When I got out I was sort of wet but not loads so i figured it was a bit of leaky pee. In actual fact I had ruptured membranes and was leaking amniotic. I spent the next 8 weeks flat on my back trying to keep all ok, as was the protocol back then.
Obviously it was way more serious than just a shaking car. ..but maybe her question wasn't so off?
Maybe there are not stupid questions?

Have a wonderful day ladies.
Re: About shaking cars. ..
dx: Unexplained IF
TTC since May 2011, 1 year trying, and then 3 TI, 2 IUI = BFN
IVF #1 (May 2013): Antagonist Protocol:
24R, 18M, 15F w/ICSI; 5dt of 2 early blasts, no frosties = BFN
IVF #2 (August 2013): Lupron Stop Protocol:
28R, 23M, 15F w/ICSI; 5dt of 1 partially hatched blast, 7 frosties = BFP
EDD 5/23/14, blighted ovum (6w6d), D&C (8w6d)
FET #1 (April 2014): transferred 2 5d blasts = BFP
C.J. born 01/09/15