The number of babies born in Auckland hit a 10-year low last year - despite a general population increase.
New Zealand's total fertility rate also dipped to a record low last year.
New data from Statistics New Zealand shows our national fertility rate was down to 1.81 births per woman - the lowest level since records started in the 1920s.
There were 59,610 live births registered in 2017.
Based on birth rates in 2017, Kiwi women would average 1.81 births over their lifetime.
Massey University professor of sociology Paul Spoonley said fertility had dropped to a "sub replacement" level, meaning the current rate was not high enough to maintain our population.
"Women are having fewer children and they are having children at a later age," Spoonley said.
While our population increased from 59,427 to 59,610 year-on-year, the number of babies born in Auckland over 2017 dropped to by more than 400 to 21,393.
This was reflective of a gradual decrease in the number of births recorded in the region.
Spoonley said this trend was not surprising alongside a general spread of New Zealand's population away from the main centres and towards the regions.
"Immigration has replaced fertility as the biggest source of population growth in Auckland," he said.
There had been a general downwards trend since 23,007 births were recorded across the Auckland region in 2007.
Meanwhile, most regions were seeing an overall upwards trend in recorded births.
Canterbury had seen a substantial increase in the number of births recorded in the region over past five years, increasing from 6,633 in 2012 to 7,065 last year.
Population statistics senior manager Peter Dolan said while the overall number of live births had increased, the fertility rate had decreased due to increased population size.
"The total New Zealand population continues to grow, driven by near-record levels of migration in 2017," Dolan said.
The total fertility rate had only dropped below 1.90 births three times before. This happened most recently in 2016, when it dipped to 1.87.
Dolan said our fertility rate had been reasonably stable for the past four decades.
It had ranged from the new record set last year - 1.81 - to a record high 2.19.
"In contrast, fertility rates increased dramatically following the Great Depression and World War II, peaking at 4.31 births per woman in 1961," he said.
"New Zealand then experienced declining fertility over the following two decades."
The reduction in birth rates since 2008 had largely been driven by trends among women aged 15 to 29.
The lower fertility rate could lead to reduced population growth if it stayed below the replacement level of around 2.1.
According to new statistics around Kiwis' death rates, the average New Zealand female had a life expectancy of 83.4 years.
The life expectancy for males was slightly lower, sitting at 80 years.