The number of children born outside wedlock is fast approaching the number born to married parents, and debate is raging over what it will mean for society.

Statistics New Zealand figures show there were just 1000 more children born to married parents than unmarried in the March quarter.

That is well down on 2000, when children born to unwed parents were outnumbered by more than seven to one.

In 1980, the gap was close to 30,000, while in 1951 just 2000 children were born to unmarried parents, compared with 48,000 born to married parents.

Victoria University psychologist Paul Jose said New Zealand was not the only country reaching a similar tipping point. Cultural, religious and legal changes were likely to be behind the shift, but it was difficult to tell what the long-term effects might be.

Family First's Bob McCoskrie said the trend was a "warning light on the dashboard".

"[It is] a key driver behind a number of social issues, including poverty and the welfare of kids."

He said statistically, both adults and children benefited from strong, stable marriage.

Married couples tended to be wealthier and their relationships more stable.

In Waikato, solo-parent support group Birthright said the levelling out of birth rates inside and outside marriage was a positive thing.

"People realise that what's important in families is the children having the support network around them, and whatever that support network looks like is OK, as long as the kids are well looked after," manager Rebecca Fraser said.

"So whether it's a married couple, whether it's a de facto couple, whether it's a mum and a grandma, whether it's two females or a lesbian couple . . . that's fine."

She said society's ideas on marriage had changed. People realised children could be raised in diverse family situations.

"I don't think it matters to kids any more whether their parents are married or not."

Family counselling organisation Relationships Aotearoa said marital status was not the most important factor in raising children.

"That's not the issue. The issue is: are they being born into strong and healthy relationships?" Midlands regional manager Ash Smart said.

Children needed to be in a home with love and warmth, he said, and evidence showed having their biological parents around increased the likelihood of this.

Mr Smart said there were many reasons why more children were being born outside marriage, including the fact relationships lasted for a shorter time than they did two decades ago.

It was not uncommon for Relationships Aotearoa to work with people who were with their second or third partner, something that was far less prevalent 20 years ago, and the numbers of families with children born to different fathers or mothers was increasing.

BIRTH STATISTICS

Births to married and unmarried couples

Fifty years ago, 8 per cent of births were ex-nuptial.

Last year, 48 per cent of births were ex-nuptial.

About 80 per cent of Maori women give birth ex-nuptially.

About 50 per cent of Pakeha women give birth ex-nuptially.

About 13 per cent of Asian women give birth ex-nuptially.

15 in every 1000 ex-nuptial births is to a woman aged between 40 and 44.

25 in every 1000 ex-nuptial births occur to women aged between 15 and 19.

Source: Statistics NZ