A sudden child-bearing spurt among women in their thirties is driving up the number of babies born in the country.
New Zealanders had 5.7 per cent more babies between September 2003 and September 2004, deviating from the trend of falling birth rates in most developed countries.
Experts said the spurtwas unlikely to last.
"This looks to be a temporary phenomenon dependent on this particular pattern of very delayed childbearing," said Ian Pool, professor of demography at Waikato University.
"The detailed analyses we've done show quite contrary factors operating for the longer term."
There were 58,380 live births in New Zealand during the past year compared with 55,210 in the previous year, Statistics New Zealand has reported.
That's because women in their thirties - also known as the last of the baby boomers - are finally having children, Mr Pool said.
But because there will be fewer women entering the age group where the delay is occurring, the birth rate is likely to fall again soon, he said.
New Zealand's birth rate peaked at 60,460 in 1991, then dropped steadily until 2002. For the past two years, birth rates have risen.
Bill Boddington, a senior demographer at Statistics New Zealand, agreed figures from the past two years may not represent a permanent change of course.
"It's very difficult to say whether that represents a shift trend or it's just annual volatility," Mr Boddington said.
Between September 2003 and September 2004, the median age of women giving birth was 30.2 years, up from 28.5 years in 1994 and 24.9 in the early 1970s.
Women aged 30-34 had the greatest birth-rate at 120 births per 1000 women.
They were followed by women aged 25-29, with 111 births. The 20-24 age group had just 72 births, down from about 200 in the 1970s.
The average New Zealand woman had 2.02 children during the past year - a birth-rate higher than that of most European countries and Australia, but lower than in the US.
Life expectancies increased to 81.2 years for a newborn baby girl and 76.7 years for a boy, representing increases of 1.5 years and 2.3 years since 1997.
