She encountered a Tuvaluan woman who had given birth four times in New Zealand - and not paid a cent towards the care she received.
After the birth the midwife was told the hospital had a "massive file" on the women, who owed about $12,000.
Other cases are less deliberate. A 29-year-old man on a working holiday visa owes $185,000 after suffering an acute bout of pancreatitis - with no insurance to cover his treatment.
Figures released under the Official Information Act show that before the new policy, medical bills for foreign patients ballooned to a record $29.6 million in the 2010/11 financial year, up from $22.2 million three years earlier.
But this fell to $16.8 million last year, according to provisional figures.
In recent years, hospitals demanded proof that patients are eligible for free treatment. Those without evidence, such as a passport or birth certificate, had to foot the bill themselves or were chased by debt collectors.
Those eligible for state-funded care include citizens and permanent residents, Australians, Britons, holders of a two-year or longer permit, refugees and accident victims covered by ACC.
A recent Auditor-General report said there was concern that the policy was "unreasonable" for vulnerable citizens, such as the elderly, who may not have the proper documentation to hand.
Health Minister Tony Ryall said public health services will never turn away any patient - eligible or not - in an emergency.
Mr Ryall confirmed that most New Zealanders will no longer have to prove their citizenship or residency to receive free healthcare because of changes to the National Health Index (NHI) database. From the middle of next year, New Zealand citizenship will be able to be data matched with NHI numbers.
"This will effectively identify those not eligible for publicly funded health services. We had to take action like this because many people don't like being asked to prove they are New Zealanders - especially elderly people who were either born here or came here a long time ago."
Those identified as non-eligible are warned they will be liable to pay. But the decision on whether to treat or not is made by clinicians on a case-by-case basis.
Auckland, Counties Manukau and Waitemata are the three worst affected boards, as the Auckland region has the most immigrants. Bruce Northey, general counsel for the Auckland DHB, says matching identities with citizenship records as part of the National Health Index is "good news".
"At the moment, we ask everyone to prove eligibility and people get annoyed."
Mr Northey said Auckland DHB had been diligent in screening patient eligibility and chasing debt, because of the pressure to balance budgets. A record bill of $18.1 million in 2010/11 dropped to a provisional $8.5 million last year.
The Office of the Auditor-General has also scrutinised debt collection and ineligible patient identification for district health boards in 2010/11.
"We will continue to monitor the Ministry [of Health] progress in helping DHBs to improve identification and recovery of the cost of treatment/and or subsidy of ineligible patients, in a way that is effective but not onerous for New Zealand citizens, especially the vulnerable."
Bad debts
* A 55-year-old from south Asia on a visitor visa owes $64,000 for treatment for heart disease after he suffered a heart attack while on holiday. His two sons are New Zealand residents and he was issued a visitor's visa as self-sponsored because he had $1000 in the bank for incidentals.
* A 29-year-old man from the United Kingdom on a working holiday visa owes $185,000 after suffering an acute bout of pancreatitis.
* A 70-year-old Pacific Island man owes $41,000 for surgery to amputate a toe due to complications arising from diabetes. His son, who lives in Australia, is his sponsor.
