The bill was resoundingly passed by the lower house following a 2013 conscience vote but the upper house delayed debating it against a backdrop of mounting controversy.

The bill formally lapsed on Thursday, after a last-ditch compromise proposal by the Christian Democrats never materialised.

"We're really relieved," said Melanie Fernandez, the chairwoman of the Women's Electoral Lobby. "Once foetal personhood is introduced, it's a thin edge of the wedge."

The bill will now need to be reintroduced to parliament, which advocates say they will do - but in an amended form that does not define an unborn child as a legal person.

The push for the bill began with the case of Brodie Donegan, whose unborn daughter Zoe died in 2009, after Ms Donegan was hit by a drug-affected driver while walking.

Ms Donegan said a judge was unable to fully account for the death of her child in sentencing the driver, who was given a nine-month prison term.

The law sought to grant legal status to the unborn, to allow for greater punishment for those who harmed them.

Fred Nile, the leader of the Christian Democrats, looked poised to mount a last-minute attempt to shepherd the bill through the upper house this week.

Mr Nile was circulating an amendment to the bill that would have imposed a controversial "sunset" clause that would have seen it expire after two years, in an attempt to blunt concerns about abortion restrictions.

Calls to Mr Nile's office were not returned by deadline.

Ms Donegan said she began working with Liberal MP Chris Spence to introduce the legislation in 2012, after Mr Nile introduced his own bill.

Ms Donegan, who does not oppose abortion, says the response was drafted hastily and had perceived implications for abortion rights she never intended.

"We were probably slightly naive about the foetal personhood part of the law; we didn't perceive it to be a problem," she said.

Ms Donegan has had provisional discussions with Liberal MLC Marie Ficarra about introducing another bill in the next parliament.

But she says she will now seek to consult  groups such as the Bar Association to ensure any future bill explicitly sidesteps restrictions on abortion.

"[There] needs to be an exemption for the mother at all costs [...] and we [don't] want to put doctors or obstetricians in harm's way," she said.

Helen Westwood, a Labor MLC and opponent of the law, said she was open to compromise that did not limit women's reproductive rights:

"We have got to listen to these women and find an alternative [law]," she said. "I think it can be done."

NSW Greens MP Mehreen Faruqi said it was "a matter of time before another foetal personhood bill or another such bill that would seek to control women's bodies is debated in Parliament.

"It is therefore critical that we build the campaign to remove abortion from the Crimes Act," Dr Faruqi said. "It is really important that we recognise the deep tragedy of a woman's loss during pregnancy in an accident; however, foetal personhood is not the answer."