The numbers were leaked to RNZ after the DHB and Ministry of Health communications staff said this week they didn't know the vaccination rates among pregnant women because they didn't collect the data.
University of Auckland obstetrics and gynaecology professor Dr Michelle Wise said: "Just being pregnant alone is a risk factor for having moderate to severe Covid infection, to be hospitalised, to be admitted to intensive care, and this is what we've seen everywhere.
"The most recent study that came out was from the United Kingdom where they reviewed all the patients that were admitted to intensive care during the Delta outbreak and in fact one out of five of them was a pregnant, unvaccinated person."
There are 24 active cases of Covid-19 in Northland, and the infection risk to babies was seen in Whangārei this week when a 6-week-old with Covid was admitted to hospital.
"That is such a tragedy for a baby to get Covid infection when we know that the pēpi can be protected from the antibodies that the mum makes when the mum gets the vaccine," Wise said.
Te Tai Tokerau was already fighting vaccine hesitancy when the pandemic began.
On average, one in five Northland babies has not had their routine immunisations by the time they are 8-months-old.
Kawakawa midwife Wiki Davis (Ngāpuhi, Ngāti Hine, Ngāti Manu) - who did not leak the DHB figures to RNZ - is caring for 23 pregnant women but only a third have had Pfizer shots.
"Any number of research articles that I offer to them or discuss with them, doesn't appear to be changing their minds.
"I have not been very successful in getting women to go ahead and have a vaccination.
"I have had one or two successes but not nearly as many as I would have thought, or I had hoped for."
Her midwifery business partner is unvaccinated and is leaving the profession before mandates start on Monday - leaving Davis with a lot more mahi, practising on her own.
"I absolutely respect her decision to do that... Although I have chosen myself to be vaccinated."
One unvaccinated pregnant mum, from Whangārei, told RNZ she had had mixed messages about inoculation, that made her anxious.
"I can't sleep already, and then you're struggling with that, and you're like 'ah I'm having more family' and so your anxiety goes up, and then the whole set up for complications is set when you're having fear and anxiety, and stress.
"There's definitely an overload of information," she said.
She has had to change midwives, because of the vaccine mandate rules.
Those who are unvaccinated and pregnant are five times more likely to have a baby prematurely, that needs neonatal intensive care, if they get Covid-19.
Although pregnant women were not included in the initial trials of the Pfizer vaccine, subsequent, large-scale surveillance has shown no harm to pregnancy.
Te Pūnaha Matatini published research this week showing those who are hapū, and those trying to conceive, are being "exploited" by vaccine misinformation.
One of the authors, Kate Hannah, told RNZ this information "had been quite visually framed".
"A lot quite emotional content that's visually upsetting, around concerns around pregnancy, bleeding and miscarriage."
She said those wanting to debunk vaccine mistruths shouldn't just provide scientific evidence but also personal reasons for vaccination, like protecting whakapapa.
Overall in Te Tai Tokerau, one in five people are still unvaccinated.
The region is 14,000 shots away from the 90 per cent target for single doses, more than any other DHB in the country.
The Northland DHB would not disclose its Covid-19 vaccination rates among midwifery staff and contractors to RNZ.
Research published in 2018 in the New Zealand Medical Journal showed only two-thirds of midwives had high confidence in vaccines.
