A controversial bill that would require women to get an ultrasound before an abortion is now in doubt after Virginia Gov. Robert F. McDonnell diluted the measure Wednesday by making it optional in many cases.

The legislation initially sought to require ultrasounds, which early last week prompted opponents to raise concerns over the procedures’ potentially invasive nature. In many cases, the ultrasounds would require a vaginal probe to establish gestational age.

On Wednesday, citing concerns over that intrusiveness, McDonnell (R), an abortion opponent who had repeatedly said he would sign the bill, asked state lawmakers to amend the measure. House members approved the governor’s amendments, but the bill’s Republican sponsor in the Senate said she would try to pull the measure for the session.

“Mandating an invasive procedure in order to give informed consent is not a proper role for the state,” McDonnell said in a statement. “No person should be directed to undergo an invasive procedure by the state, without their consent, as a precondition to another medical procedure.” He did not comment further.

Confusion over the legislation and ultrasounds — and considerable national media attention — preceded the unraveling of the bill. The original measure stated, simply, that a woman needed an ultrasound before an abortion. Many lawmakers did not understand that at the young fetal age abortions usually occur, the invasive vaginal ultrasound would be needed to establish gestational age, as required by the bill.