Almost 90 per cent of maternity wards in New Zealand hospitals have no senior doctors or consultants on site at night.
The revelations raise questions about patient safety in the event of traumatic or complex births that occur after-hours and require urgent specialist care.
Information provided to the Herald under the Official Information Act showed most senior doctors went home by 5pm with only two hospitals having a consultant on site at all times to deal with complex cases.
Weekend cover was not much better, with senior staff only onsite for morning or evening rounds rounds in six regions while Canterbury's on-call specialist often stayed overnight at the hospital due to workload throughout the week.
The rest relied on midwives, nurses and junior doctors, including registrars and house officers, to look after patients in the evenings and weekends.
Though midwives and junior doctors were available throughout the night, on-call consultants could take up to 30 minutes to arrive at hospitals, with delays potentially the difference between life and death.
Research from Britain suggested about 70 per cent of births were outside normal working hours and peaked at 4am.
It also found weekend babies were more likely to die or suffer a serious injury.
District health boards in New Zealand blamed staffing pressures and funding constraints for lack of after-hours senior doctors and consultants.
In 2015 the Health and Disability Commissioner criticised Capital and Coast DHB after the death of newborn baby .
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The little girl died soon after a horror early morning delivery, for which a trainee specialist - who sought advice from an on-call specialist by phone before beginning an emergency caesarean - admitted to being "out of my depth".
Earlier interview with grieving father
And the Herald revealed last month that a senior doctor on call the night a baby suffered fatal injuries during birth at Waikato Hospital was called twice by a concerned midwife before attending.
Baby Hohepa Hemara Walters-Hughes died on April 5 after his mother, Melanie Hughes, suffered a ruptured uterus during labour. The family are now asking if their little boy could have been saved.
Doctors did not work in primary birthing units not directly run by a hospital so all women who developed complications birthing in those units or at home were taken to a hospital for care.
Responses from 18 of the country's 20 district health boards showed only Counties Manukau District Health Board and one of the two hospitals in the Waitematā DHB area, Waitākere Hospital, had a specialist on site after hours.
Hospitals in the other regions relied on on-call consultants who could be half an hour away.
Lakes DHB, centred on Rotorua, told the Herald it served a population of 110,000 and "was not large enough to be funded to employ further consultant obstetricians to provide on-site 24/7 cover".
"An obstetrician is rostered on call during these hours and they are always available for telephone advice, and to be called in to work if necessary."
Taranaki DHB said it had only five obstetrician/gynaecologists. It was not possible for them to be physically present at the hospital 24 hours a day.
New Zealand College of Midwives chief executive Alison Eddy said things could go wrong "very quickly" and tragedies did occur.
But there were strong collegial arrangements in hospitals between midwives and senior consultants to care for birthing mothers.
Most emergency C-sections were performed due slow-progressing labours and were not usually due to women or babies being in severe distress.
In many hospitals it was not practical to have specialists on deck 24/7.
"It's really trying to find the right balance."
Eddy agreed about 70 per cent of Kiwi births occurred after-hours.
"They're not born Monday to Friday, 9-to-5."
But Voice for Parents, a group which helps families deal with traumatic births, said the delay waiting for a specialist could contribute to mental health issues after the birth even if there was no physical effect.
The group's spokeswoman also highlighted the pressures placed on midwives and junior doctors not to call a consultant back in unless it was for a "damn good reason", meaning junior staff could be more reluctant to ask for a specialist's opinion or help.
"I recall working in delivery suite and the on-call obstetrician saying to me, as he was about to head home, 'I'd better not be called away from my rugby game tonight.'
"I'm sure he'd defend himself saying it was just in jest, but I knew that it was a warning of sorts," she said.
Women's Health Action general manager Isis McKay said DHBs were required to adhere to Ministry of Health service specifications in terms of specialist staffing.
"I would expect that if they're a tertiary facility they should have someone with the specialist skills and training on the ground 24/7."
The Royal College of Obstetricians and Gynaecologists did not respond.