About a third of pregnant women admitted to intensive care units and high dependency units in New Zealand had potentially preventable severe illnesses.
Another 29.5 per cent were not preventable but better care was needed.
The findings are the work of a study conducted by researchers at Victoria University of Wellington, Te Tātai Hauora o Hine Centre for Women's Health Research and the University of Otago.
Professor Beverley Lawton, lead author on the study, said these women did not need to get as sick as they did and called the ethnic disparity in standard of care "unacceptable".
Overall 6.2 women per 1000 pregnancies were admitted to New Zealand intensive care units (ICUs) and high dependency units (HDUs) because of these life-threatening complications during pregnancy, the study shows.
Pacific women were the most likely to be admitted at a rate of 10.4 per 1,000 deliveries, compared with 4.6 for New Zealand European women.
The rate for Māori women was 5.6, for Indian women 7.2 and for other Asian women 8.2.
The three most common reasons for admission to an ICU or HDU were major blood loss, preeclampsia-associated (toxaemia) conditions or severe sepsis (infection).
During the study, multidisciplinary review committees reviewed 339 anonymised severe maternal morbidity (SMM) cases in depth examining potential preventability.
They asked the question "Should this woman have gotten as sick as she did?", and they found that only 36.5 per cent of cases were managed appropriately.
The six multidisciplinary review committees included 10–15 clinicians from a pool of more than 200 expert obstetricians, anaesthetists, intensivists and midwives from all 20 district health boards.
The rate of potentially preventable admissions with severe illnesses to ICUs and HCUs was 2.1 per 1000 deliveries overall.
It was higher at 3.6 for Pacific women, more than double the rate for New Zealand European women of 1.5.
The rate for Indian women was next highest at 2.9, followed by other Asian women at 2.5.
The rate for Māori women was 1.8.
The findings show that substandard care such as delay in diagnosis or inappropriate treatment occurred in more than 90 per cent of preventable SMM cases and system factors such as lack of treatment protocols and delays in getting to operating theatres occurred in 60 per cent.
The study showed that substandard care and system issues were present for all cases of preventable SMM in Pacific women, with patient factors contributing only 7.5 per cent of preventability, which contrasts with widely held views that women themselves are often to blame for their illness for reasons such as non-compliance.
The study was published in January 2019 in the international obstetric journal Acta Obstetricia et Gynecologica Scandinavica (AOGS) and Professor Lawton said its findings were compelling.
"It is very concerning—women should not suffer avoidable harm," Lawton said.
"The ethnic disparities are unacceptable.
"But the good news is these issues are fixable."
For example, although severe infection or sepsis was the third most frequent cause for admission to ICU and HDUs it was deemed the most preventable, with 56 per cent of cases deemed potentially preventable.
"This can be addressed by the maternity sector with clinical and DHB-led programmes," Lawton said.
"Urgent action is needed. Expert independent review enables us to inform, direct and evaluate programmes for change so we can reduce the considerable impact of harm for these women and their whānau."
Based on the success of the study, the Ministry of Health has translated this model into a SMM case review process through the Health Quality and Safety Commission.
This study was funded by the Health Research Council of New Zealand and the Ministry of Health.