For the first time in New Zealand two women can be named on a child's birth certificate as "mother" for children conceived using assisted reproductive techniques.

Jess and Stacy complained to the Human Rights Commission, who raised it with the Department of Internal Affairs (DIA).

The women both wanted to named as mother on their daughter Evie's birth certificate.

The lawyer who advocated for the "massive" change said it could affect more than 1000 children.

Solicitor and barrister Stewart Dalley, at Ryken and Associates, took on the case on a pro bono basis, after reading of their plight in the Herald last year.

Evie was conceived using donor sperm and IVF.

At the time, Jess told the Herald it had been frustrating when it came to filling out official documents.

Jess had to list her name under "other" on Evie's birth certificate and under "father" on their online application for an accommodation supplement.

"It's not good. Biologically she's my child and we're both equally Evie's mother.

"All they have to do is put a 'm' in front of 'other'. It's not difficult."

Dalley said initally Internal Affairs held the position that there were legislative reasons for the stance.

"But this was news to me but when I looked at that I thought I couldn't see any legislative reason why that would be."

Many letters and views were exchanged over the course of several months, he said.

"Eventually the department said 'yeah, you're right' there is no reason for this'."

Two women can now be listed as "mother" and "mother", or "mother" and "parent", on a birth certificate.

Women who have previously been dubbed as "other parent" on their child's birth certificate can contact Internal Affairs and make the change if they choose.

This would come at no cost to the people who wanted to make the change.

Dalley said it was about recognising the legal parents equally and also recognising that not all people identify with a gender.

"This labelling of 'other parent' sounded a bit like you were subordinate somehow, that you were not a real parent.

"All credit to the Department of Internal Affairs for coming on board."

Dalley and his partner were the first same-sex de-facto couple in New Zealand to jointly adopt.

"We won that case a couple of years ago, so I was aware of this issue."

But sometimes it was about waiting for the case to come along, he said.

"Here's the opportunity to change it."

An Internal Affairs spokesperson confirmed that the recording of parental titles on certificates, including births, marriages and deaths, had been expanded.

"The change will enable two female parents to both be recorded on a birth certificate as the child's 'Mother', where that child was conceived using assisted reproductive techniques [such as artificial insemination].

"Previously if the mother married or entered into a civil union or de facto relationship with a woman who consented to the mother undergoing the procedure, the details of the mother's partner could only be recorded as the child's 'parent' on birth certificates."