A groundbreaking study has found that more than one in every six women who have ever been pregnant in Auckland have had an abortion.
The abortion rate rises to one in every three among women of Asian ethnicity, and is also above-average for younger women and for women who have suffered domestic violence.
The rate is lower for rural women in the Waikato, where only one in nine has had an abortion.
The figures have been published in two new papers stemming from a survey of about 1400 women aged 18 to 64 in Auckland and a similar number in rural Waikato in 2002, which was focused on finding the rates of domestic violence and associated factors.
The new papers show, not surprisingly, that domestic violence is associated with higher rates of both intentional abortions and accidental miscarriages, as well as with higher rates of drinking, smoking and unwanted pregnancies.
But lead author Janet Fanslow of Auckland University said the surveys also provided the first-ever measures of the prevalence of both abortion and miscarriage in New Zealand.
The overall abortion rate of 14 per cent among all women who have ever been pregnant was much lower than in the United States, where 29 per cent of ever-pregnant women under 45 had had an abortion, according to an official survey in 1995.
But the New Zealand abortion rate for women who have been pregnant but never suffered domestic violence (10 per cent) was comparable with World Health Organisation surveys using the same methodology in Japan (12 per cent) and Brazil (9 per cent).
The figures, though never measured before, are no surprise given a steady rise in the number of abortions in New Zealand from 10 per cent of all live births, stillbirths and abortions in 1980 to 23 per cent in 2006.
Dr Fanslow said it was not clear why the proportion of ever-pregnant Asian women who have had an abortion (30 per cent) was much higher than the rates for Maori (18 per cent), Europeans and Pacific Islanders (both 12 per cent).
"There may be differences in knowledge about or use of contraception," she said.
But it was easier to explain the high abortion rate (21 per cent) for women who have suffered domestic violence.
"Women currently experiencing intimate partner violence, or with a history of violent relationships, may feel less prepared (emotionally, socially or financially) to care for a child. This may contribute to their decisions to terminate a pregnancy," she said.
Women who have suffered domestic violence were also more likely to have had at least one spontaneous miscarriage (42 per cent) than women who had not been abused (28 per cent).
The study found that 6 per cent of the Auckland women who had been pregnant, and 9 per cent of the rural Waikato women, had been beaten or physically assaulted by a partner while they were pregnant. For three-quarters of them, the violence started before they became pregnant.
Maori women were much more likely to have suffered violence during pregnancy (22 per cent) than Pacific women (7 per cent), Europeans (6 per cent) or Asians (1 per cent).