Nearly 4000 more babies were born in New Zealand last year than in 2014, an increase of 7 per cent. It was the first time in four years the number of births has risen rather than fallen.
Statistics New Zealand today released numbers that showed there were just over 61,000 births last year, up 3796 from 2014.
READ MORE: Teen pregnancy falls as birth rates rise.
"Higher fertility rates and population growth led to more births in 2015," population statistics manager Jo-Anne Skinner said.
"The rise in births follows decreasing numbers in the preceding four years."
Statistics New Zealand statistical analyst Anne Howard said she was not surprised by the increase as it followed a trend since 1980 where births would decrease for a few years before bouncing back again.
"There's been a very long period of what we call the total birth date being at around two births per women and that's been the trend since about 1980. But that hides quite a lot of change, because in that period we've seen a shift in the age at which women have their babies. They have them at an older age now.
"We're seeing overall the birthrates being fairly consistent over a long period of time but from year to year we're seeing periods where the numbers will decrease before going back up again."
Mrs Howard said it was hard to assess why birth rates were so steady over the past three decades, adding there was no consensus among demographers about what exactly drove birth rates up or down, particularly because each country's birth rate seemed to respond differently to criteria such as welfare policies, employment levels and pronatal programmes.
Statistics New Zealand found women aged 30 to 34 years have had the highest fertility rate of all age groups since 2002, and last year nearly 1400 more babies were born to women in this age group than in 2014, in part because there are more women of this age in New Zealand now.
Teenage fertility rates have continued to drop each year since 2008. Last year, the rate for women aged 15 to 19 years was 19 births per 1000 women, down from 33 in 2008.
The numbers of deaths in New Zealand also rose but by a smaller amount. Only 545 more deaths were recorded last year than in 2014.
Deaths have gradually increased over time due to population growth in the older age groups, although this was partly offset by longer life expectancy, Statistics New Zealand said.
The median age at death last year was 78 years for males and 83 for females. Only 19 per cent of those dying were aged under 65.
According to the latest abridged period life table released by Statistics New Zealand, life expectancy rose marginally for 2013 to 2015 compared to 2012 to 2014.
Women in their mid-30s can expect to live on average a further 49 years. For blokes of the same age the outlook was slightly bleaker, offering only another 46 years on average.
However statistical analyst Kim Davis said those predictions were based on death rates in the past three years, and didn't take into account the high likelihood that life expectancy would keep getting longer.
"For people thinking about retiring at age 65, these figures are an underestimate," Mr Davis said.
He said they shouldn't take the 19 (men) or 21 (women) years on average the table predicted they had left as gospel.
"[The current period life table] depends on the death rate remaining the same for the rest of your life, which of course isn't particularly realistic because death rates always continue to change, usually downwards.
"As you move throughout your life the death rates will almost certainly be lower than they are now."
He said cohort life tables were more meaningful as they took into account future changes in death rates at each age.
The cohort life table would be updated next month, but for people wanting to guess their life expectancy now, the Statistics New Zealand website has an interactive calculator, How long will I live?.
Based on birth year and gender the calculator predicts average life expectancy based on last year's cohort life table data.