The Auckland District Health Board has sought advice on stopping women living outside its boundaries from using its facilities for booked inductions and caesarean sections.
Restrictions would be highly controversial, mostly affect women on the North Shore and in West and South Auckland, and pile pressure on neighbouring hospitals.
The DHB told the Herald there are no "immediate" plans to change policies for booking Auckland City Hospital secondary birthing facilities, used for interventions like inductions. Any reforms in future "will be carefully developed and introduced".
"We have never turned away a woman who needs our care," said Dr Robert Sherwin, director of women's health.
"However, planned obstetric procedures consume resources ... although we are able to safely manage current demand for these secondary services for non-resident women, it is essential that we develop plans to manage future demand."
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The Auckland region has three DHBs - Auckland serves central suburbs , Waitematā covers West and Northern areas, and Counties Manukau in the South, including Pakuranga.
Documents obtained under the Official Information Act reveal hospital bosses raised serious concerns with the Ministry of Health about women from outside of its catchment area being booked for procedures, instead of at their home DHB.
The DHB briefed ministry officials this year on the numbers of non-resident women using facilities - between about a third and 50 per cent on any given day.
"These numbers are rising each year, and are having a significant effect on our service," a DHB staff member wrote in a January email.
'We don't have enough' - hospital begs for help as it turns away patients
"At the core of my role as midwifery consultant is quality and safety across the women's maternity journey, and I see this issue as a key variable to this ... we really need support with this."
In response, the ministry's principal adviser for maternity, Bronwen Pelvin, sent through a letter that "sets out your authority to develop a maternity booking policy", and noted that the priority population for DHBs are those living within its district.
Pelvin predicted the issue was "likely to produce tensions" and strongly encouraged Auckland DHB to talk to Waitematā and Counties about any changes. In a further email to a colleague, she explained the situation.
"The women are not there because they require the level of tertiary maternity services (maternal fetal medicine, neonatal intensive care or other specialist services) but because they have chosen LMCs (obstetricians and midwives) who only provide care in ADHB," Pelvin wrote.
"They [Auckland DHB] cannot supply enough registered midwives, obstetricians and other staff to service this level of demand. They really want to take this on as the services the women require are readily available in their DHBs of domicile.
"Auckland DHB has a duty of care to its resident population and also to provide a safe and sustainable working environment for its employees. They know they cannot do that if a third of the people are coming from elsewhere.
"They believe that dropping the services back to the Auckland district (plus the tertiary services and the few women who just 'pop in' from other DHBs) will enable them to take the pressure off the staffing ... if Auckland was one DHB then different decisions would be made and the necessary staff deployed to where they are needed. But it's not!"
Other health boards face their own pressures, particularly Counties Manukau DHB, which took urgent steps after the death or stillbirth of babies in 2016 and 2017 were linked to problems such as a lack of staff and bedspace. Poverty and obesity rates have contributed to big increases in the number of pregnancies needing more hospital care and monitoring.
Middlemore Hospital's clinical director of women's health, Dr Sarah Tout, said many Counties Manukau women gave birth at Auckland City Hospital because they used a private obstetrician.
Counties "has been chronically underfunded for years", she said, and it would be disappointing if more workload was put on its services without that being addressed.
Dr Robert Sherwin of ADHB said there were several reasons why a woman's midwife or private obstetrician booked at Auckland City Hospital, including wanting to work from one hospital, regardless of where their patient lived. The hospital was currently able to provide safe care despite the demand.
"I want to assure all women who are booked to give birth at Auckland City Hospital or who are intending to give birth in our care that there will not be any immediate changes to our policies or procedures," Sherwin said.
"We have been talking with other DHBs, and will seek input from our staff, the LMCs [lead maternity carers] who work at Auckland City Hospital, patients, whānau and other stakeholders, such as our union partners and the appropriate professional colleges."
How DHBs work together and whether some could be merged is expected to be addressed in a sweeping, Government-commissioned review into the whole health and disability sector. Recommendations from the review are expected in March next year.
Auckland DHB has had discussions with the Ministry of Health about the demand on its secondary maternity facilities at Auckland City Hospital, particularly from women who don't live within its boundaries.
Secondary facilities are designed for women and babies who experience complications and might need some sort of intervention like a caesarean section. These can be planned and booked in advance.
In the wider Auckland region, such facilities are also located within Middlemore Hospital, North Shore Hospital and Waitākere Hospital. Lead maternity carers (LMCs) sometimes use one hospital as their base for all planned procedures, regardless of where their patient lives - and this has put pressure on Auckland City Hospital.