Virginia's state senate has decided against passing a controversial bill that would have defined life as beginning at conception, instead referring the legislation back to the committee stage and deferring a decision until 2013.

HB1, the so-called "personhood" bill, will not be considered again until next year after the senate voted 24-16 in favour of returning the bill to the state's committee on education and health.

The move comes a day after the state's governor, Bob McDonnell, an anti-abortion Republican, performed a U-turn on his support for a bill that would have forced women to undergo transvaginal ultrasounds before being granted abortions.

McDonnell, seen by some in his party as a possible candidate for vice-president, had previously said he would sign the bill if it were passed by Virginia's general assembly.

But after mounting pressure from campaigners, Democratic delegates and ordinary Virginians who strongly opposed the measure, McDonnell changed his position, saying he would only review the bill if it appears on his desk.

The personhood bill would have defined a fertilised egg as a person and had been opposed by a coalition of groups supporting women's rights in Virginia and by Democrat committee members.

The legislation stated that the laws of Virginia "shall be interpreted and construed to acknowledge on behalf of unborn children at every stage of development all of the rights, privileges and immunities available to other persons, citizens and residents".

HB1 had been passed to the senate after the Virginia state committee on education and health passed the bill – eight Republican members voting for it and seven Democrats against. In the Senate, however, made up of 20 Republicans and 20 Democrats, members voted 24-16 to recommit it to the education and health committee.

Local news channel WDJB7.com reported that senate majority leader Tommy Norment had said he came away from a hearing on Thursday morning with concerns about the complexities of the issue raised by a variety of speakers.

Virginia has found itself under national scrutiny this week for moves to pass the two pieces of legislation, seen as two of the most controversial anti-abortion bills in recent history.