PORTSMOUTH, Virginia (Reuters) - Virginia lawmakers on Wednesday passed a revised ultrasound requirement for women seeking abortions after Republican Governor Bob McDonnell shifted his stance on the hotly contested measure. The vote by the House of Delegates approved legislation that would require women to undergo a non-invasive ultrasound with the option of a more invasive probe if deemed necessary by a doctor. McDonnell, an abortion opponent and possible contender for vice president, previously had spoken in favor of the original measure that would have made internal ultrasounds mandatory. That version of the bill has been lampooned on national television and drew a large crowd of protesters to the state capital in Richmond earlier this week. Critics delivered to the governor a petition with more than 33,000 signatures opposing the bill, said NARAL Pro-Choice Virginia Executive Director Tarina Keene said. Just prior to the 65-32 House vote on Wednesday, the governor issued a statement indicating he had withdrawn his support for the broader measure. "Mandating an invasive procedure in order to give informed consent is not a proper role for the state," McDonnell said. I am requesting that the General Assembly amend this bill to explicitly state that no woman in Virginia will have to undergo a transvaginal ultrasound involuntarily. Some critics bashed the amendment, saying only an invasive ultrasound can detect the fetal heartbeat during the first trimester of pregnancy. The amended House legislation now will be sent back to the state Senate for a vote. Six other states have passed laws requiring abortion providers to perform an ultrasound on each woman seeking an abortion and give the woman an opportunity to view the image, according to the Guttmacher Institute, which studies reproductive health issues. Editing by Colleen Jenkins and Paul Thomasch