This isn't as silly an idea as it sounds. Pregnant women, even if convicted of witchcraft, would not be executed so long as they remained pregnant. The theory is that even if you deserve death, the baby inside you does not--so the officials will put off your execution. This was called "reprieve for the belly."
Of course, you still might be executed eventually, but the hope is that the hysteria won't last another nine months.
One slight problem, however. Who will you find in jail to impregnate you? Sorry, this option is not available: Try another!