A new Ministry of Health report has found the teenage birthrate fell by over a third between 2006 and 2015.
But the birthrate for women over 40 increased by 15-percent over the same period. More women over 40 are having children, but such pregnancies are still rare.
Royal College of Obstetricians and Gynaecologists New Zealand chairman Dr Ian Page said the over-40 birthrate has gone from 13.3 to 15.2 pregnancies per thousand women, which is quite a small group.
Women aged between 30 and 34 have the most pregnancies of any age group.
The figures mean New Zealand is joining the club of western countries where more people are dying than being born.
The report found birth rates have been trending down since 2006, particularly for European people.
Massey University pro-vice-chancellor Paul Spoonley said New Zealand's birth rate could eventually fall as low as European countries.
He says New Zealand is going to have think quite carefully about the future, in terms of its population, its structure and its birth rate.
A third of women who gave birth in 2015 lived in deprived neighbourhoods.