A heated debate broke out at a select committee considering changes to abortion law, after some submitters asked for the legislation to say "pregnant person" instead of "pregnant woman".

The Abortion Legislation Bill - which would bring abortion out of the Crimes Act and remove the need for a doctor's approval before 20 weeks - currently uses the term "pregnant woman". 

But some submitters have asked the committee to consider replacing "pregnant woman" with "pregnant person" or "pregnant women and people" in the legislation to represent diversity.

Hera Cook, a researcher at Otago University in Wellington's Department of Public Health, argued against the change as she presented to the Abortion Legislation Committee on Wednesday.

"We would ask the committee not to use the term "pregnant person" and that this term not be used in the legislation."

She said it would "obliterate women's experiences as pregnant women".

She was followed by Jan Rivers, who describes herself as a gender-critical feminist, who told the committee she does not believe in gender identity, and "strongly" advised the MPs not to change the legislation to "pregnant person".

"If woman is replaced with person, to me that seems to be the thin-edge of the wedge of saying that we believe that people get pregnant, and not women, and therefore people who don't believe in gender identity start to be castigated."

Green MP Jan Logie, a member of the committee, said she didn't understand the problem with expanding the definition in the legislation.

"We've heard quite compelling evidence from people in their own experience as trans people who have become pregnant... that language matters."

• New gender-neutral guidelines will allow male Navy personnel to wear make-up, false eyelashes
• Petition for Massey Uni to cancel 'Feminism 2020' gathers steam
• Transgender cyclist defends her world championship win after Donald Trump Jr. calls it "BS"
• Transgender I mean Transfender

Logie argued that the Human Rights Commission has already validated gender diversity.

"What you're asking us to do is run counter to the Human Rights Commission findings to marginalise a community and contest their existence."

Cook, who is also a gun control advocate, told the committee she has "great sympathy" for the problems faced by trans and non-binary people in New Zealand.

But she said the group of researchers she works with decided they do not consider the term "pregnant person" a "useful way to understand the experience of women and their fertility".

"It's about things like pregnancy discrimination in the workplace," she added. "Is there discrimination against pregnant persons or is there discrimination against women who happen to be pregnant?

"The discrimination against women who are pregnant also extends to women who are not pregnant which is why I refer to the capacity to conceive."

Logie said it's part of a "much broader debate" and Cook agreed.

It wasn't the first heated exchange Logie engaged in over the proposed abortion law changes.

Earlier that day, she debated former Prime Minister Sir Bill English over the "conscientious objection" clause in the legislation.