Yes, it can. It was what caused my water to break two weeks from my due date! Haha! That's actually why doctors suggest sex in order to induce labor- not because of the sex itself (even though a husband's semen contains pitocin, the levels are very low) but because an orgasm will cause the uterus to contract and can cause you to go into labor. My orgasm wasn't from sex (my hubby was in A-School for the Navy at the time) but from masturbation, which doctors also tell you to do to help induce labor towards the end.
If your cervix is closed, the fluid would have a hard time leaking out- but most women tend to be at least 1 cm dilated at the end of their pregnancy, allowing the fluids to leak.
at 5:17 PM on Jan. 14, 2009