Only five of New Zealand's 16 regions are producing enough babies to replace their populations without migration and none of them contains the five largest cities.
A study by Statistics New Zealand of the 2001 census shows the most fertile regions are Northland, Waikato, Bay of Plenty, Hawkes Bay andGisborne.
Chief demographer Mansoor Khawaja told the Weekend Herald that in 1986 that list had also included Taranaki and Manawatu, but those regions were now recording less than the replacement fertility of 2.1 births per woman.
Mr Khawaja said the regional variations were marked.
The ethnicity of regions was a factor, although he noted that while nearly a quarter of those living in the Auckland region were Maori or Pacific Islanders, that was not enough to bring the region up to replacement fertility levels.
"They are not offsetting the very low fertility of the Pakeha population."
Mr Khawaja said Maori and Pacific people had the highest fertility rates with over three births per woman.
The Maori fertility rate of women under 25 was well over twice that for Pakeha women of the same age range.
The percentages of Maori and Pacific Islanders in the most fertile regions were: Northland (33 per cent of the population), Waikato (23 per cent), Bay of Plenty (29 per cent), Hawkes Bay (26 per cent) and Gisborne (48 per cent).
Mr Khawaja said for about quarter of a century the New Zealand fertility rates had been below replacement level, about two births per woman, similar to the United States but higher than other OECD countries such as Canada, Australia and Italy.
There remained a strong contrast between the North Island, with a fertility rate of just under 2.1 births and the significantly less fertile South Island with a rate of just under 1.9.
