A new study shows mums who have midwife-led births have an increased risk of adverse outcomes.
The University of Otago research examined data on more than 244,000 births in New Zealand from 2008 to 2012.
The study found adverse events were substantially lower when births were led by doctors and obstetricians, compared with midwife-led births.
There were no significant differences between the midwife-led and medical-led births for neonatal deaths.
Study co-author and former midwife Ellie Wernham says the findings are concerning and demonstrate a need for further research.
"As a practising midwife I saw first-hand the many benefits of our midwife-led continuity of care model. However, our study has identified that there may be aspects of our maternity system where improvements can be made that provide for better outcomes for babies."
New Zealand adopted a midwife-led model of maternity care in 1990. Now, more than 80 percent of New Zealand mothers use midwives throughout pregnancy and delivery, and doctors generally only get involved when there are risk factors.
College of Midwives chief executive Karen Guilliland concedes midwives are under pressure. She says the research highlights a need for improved funding and better staffing of maternity services.
"The differences in that outcome may be explained by the way our maternity services have to operate. Most of our maternity hospitals are understaffed and often struggle to provide immediate response when midwives request medical input.
"This means that often women in labour have to wait to see a specialist, causing unacceptable delays for them and their babies. None of our main maternity hospitals have an obstetric consultant on site after hours or weekends, which are when the majority of births occur."
The Ministry of Health says the findings of the study are unexpected and require further investigation. It's referred the study to the National Maternity Monitoring Group for advice on whether further research needs to be undertaken.
The ministry adds overall rates of adverse outcomes in New Zealand are low, and are comparable to other similar countries like Australia and the United Kingdom.
Action to Improve Maternity founder Jenn Hooper says further research needs to be done as a matter of urgency.
"If there is a significant excess of adverse outcomes for midwives, we now need to find out how come."
Ms Hooper's 11-year-old daughter, Charley, was left severely disabled after two midwives were unable to resuscitate her properly at birth.
"It doesn't matter how low the numbers are. When it happens to you it's 100 percent," says Ms Hooper.