A group of women who have had abortions have spoken out to caution the prime minister on law reform.

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It follows a report back by the Law Commission that recommended ways to decriminalise abortion.

An open letter to Prime Minister Jacinda Ardern has been published as a full-page advertisement in the Sunday Star Times, Herald on Sunday and will be published in the Dominion Post on Monday.

The open letter includes the names of the eight women and the number of children they have, including those they have aborted.

It is thought to be the first time in New Zealand history that a group of women who have had abortions have spoken publicly about their experience, a statement by the group said.

Spokesperson Barbara Hill said that it was time for an honest conversation about the impact abortion had.

"We began to feel that the law was changing too fast without any investigation of the fallout and consequences of abortion."

Ms Hill could not say how much it cost to take out the three full-page advertisements.

She said the advertisements were funded by the eight women and a number of organisations, including Family First.

"What we would like to do is just draw it to the attention of both Jacinda Ardern and our MPs as well as the public that it needs to have more investigation.

"And people need to be aware - and one of the reasons people aren't aware is because it's people like me who remain silent.

"None of us have really had the courage until we all got together to actually stand up and say, 'Well we need to remind people that there's more to it than just a hospital procedure.' "

Ms Hill has worked with many women post-abortion as a mental health educator and found that many struggled with the emotional fallout.

"None of them have reported having counselling, most of the doctors seemed to be there for the medical side of things but not for the emotional side of things.

"I haven't had any evidence to the contrary that women are being well-prepared for abortion - it's been reported that mostly it's treated as a procedure and it's just some cells to get rid of."

Ms Hill said she experienced grief and a range of emotional problems that she was not prepared for following her abortion.

"Initially, I had huge relief after I had an abortion. I thought it had solved my problem - I didn't wish to be pregnant, it wasn't a good time in my life, and I thought, in effect, I could get away with it.

"but I find, particularly with my next children, it was quite a problem for me to bond with them. I was quite an angry mother and I really had to weigh up what had caused this."

However, reproductive rights campaigner Dame Margaret Sparrow said support and counselling was already available for women, and that she did not believe more support was needed.

"I mean it's sad that these women had an experience where they didn't have counselling, but my experience is that in most situations, good counselling is available."