The latest quarterly data from Stats NZ showed the ratio of births to the number of women of child-bearing age was now 1.63 - well below the 2.1 ratio needed to keep the population growing.
Or, below the number needed for a woman to replace herself, and her partner.
What that translated to, is that without migration, the population would join others around the world that are shrinking.
In the year to September 2019, there were more than 59,000 babies born in New Zealand.
By the same time this year, there were 1300 fewer born over the year.
The downward trend was not a blip on the radar - it has been a trend over the past decade said Kim Dunstan, a senior demographer with Stats NZ.
"They've shown a steady decline since about 2010, when the total fertility rate was about 2.2 births per woman."
He said reasons were less about biology than social and economic factors.
The trend was likely influenced by the rising cost and shortage of housing, which is reflected in the data that shows the decline was greatest among those aged under 35.
"Fertility rates among older women though - 35 to 50 years remain relatively the same as they were a decade ago."
Dunstan said involuntary infertility - that included men - could also be a factor.
"But generally, the trend we're seeing in New Zealand and in other countries around the world is around voluntary choice to have children, or not, and for those having children it's about the number they have over their lifetime."
A research associate at the National Institute of Demographic and Economic Analysis said the latest figures were a big drop on the same time last year.
Natalie Jackson said there was a technical explanation: more people in the country - because the data covered the period since "Covid came into our lives and played havoc with overseas travel".
"The fertility rate is essentially a ratio of births to the number of women aged 15-49 years, and there will have been a lot of women in that age group unable to leave the country, and a reasonable number at those ages returning."
Dr Jackson said those figures combined would have increased the number of women, against which the number of births was measured.
"At the same time there have been fewer births, so - fewer births and more women, means the rate will have dropped along the lines it has."
But those on the frontline were not noticing much change. Midwives were just as busy, said New Zealand College of Midwives chief executive Alison Eddy.
"What the data showed was about 1300 births less this year compared to last year, but when you spread that across the geography of New Zealand, it really doesn't equate to much at all," Eddy said.
"We have approximately 1300 midwives working in the community as lead maternity carers so you could say that on average, they may have looked after one less woman each."
Kim Dunstan said that while the latest data was influenced by Covid-19, it remained to be seen what next year's results would show.
"Until next year it won't be clear what direct impact the pandemic has had on couple's childbearing decisions."
Dunstan said the drop could continue if the labour market and economic conditions continued to deter people from having children.
