
Sperm deposited near the entrance of the vagina has been known to cause
pregnancy, even in the presence of a hymen. I doubt that sperm could make 
it through a layer of cloth then find the right path to a waiting ovum,
but it might be possible.

So, it is possible for a woman to be both virgin and pregnant.
Also, some hymens are sufficiently loose to allow near-normal intercourse
without rupturing. The problem when investigating these phenomenae is,
of course, getting an honest account of what exactly happened.