The Atlantic has an piece on the research the Congressman is referring to -- it was actually about female fetuses at 32 weeks. It includes the following passage:
"We recently observed a female fetus at 32 weeks' gestation touching the vulva with fingers of [her] right hand. The caressing movement was centered primarily on the region of the clitoris...these light touches were repeated and were associated with short, rigid movements of the pelvis and legs. After a break, in addition to this behavior, the fetus contracted the muscles of the trunk and limbs, and the climax, clonicothonic movements [rapid muscle contractions] of the body, followed. Finally, she relaxed and rested. We observed this behavior for about 20 minutes."
So Dan, the only evidence in the scientific literature is for girl fetuses rubbing it out. Dirty, dirty girls.