New Zealand mothers are getting older while the birth-rate continues to languish below the replacement level.

According to figures released by Statistics New Zealand yesterday, annual birth rates for the December 2005 year suggest New Zealand women average 2.0 births - the same as for the last decade.

The total fertility rate required for a population to replace itself without migration is 2.1 births per woman.

Sub-replacement fertility is common among developed countries.

But New Zealand is marginally more fertile than Australia, which has only 1.8 births per woman, and England and Wales (1.7).

Government statistician Brian Pink said while the total birth rate had been relatively stable, there had been "a significant shift" in the timing of births.

Last year, women aged 30-34 had the highest birth rate of 120 births per 1000, while in 1995 it was women aged 25-29 with 123 per 1000 births.

The median age of New Zealand women giving birth is now 30, compared with 29 in 1995 and 25 in 1975.