Paterson said this had big implications not only for mothers, but for their entire family.
"Perinatal depression is the leading cause of maternal deaths.
"For her children, it means an increase in emotion, cognitive, and physical development issues, and a higher risk of insecure attachment.
"Later in life her child is at risk of developing learning difficulties, mental illness, addictions, delinquency and even suicide."
Paterson said the research found it wasn't an attitude problem from the midwives, but a lack of knowledge of both how to spot the problem, and then address it.
She said midwives were singled out because they were the health professional a woman saw the most through pregnancy.
But it was also a wider problem with mental health in general.
"A woman can go to an antenatal class and not hear about perinatal depression," Paterson said.
"They can go to their midwife and not hear about perinatal depression.
"They can see their GP, go to Plunket, and never be told about it.
"Yet, if she develops symptoms, the way it's set up is that she's expected to seek help on her own."
Paterson believed part of the problem was a lack of funding and priority for mental health programmes.
"Mental health has always been the poor cousin to physical health.
"I think one of the reasons is it's not particularly sexy.
"It's a group of people who generally don't have a voice, they're vulnerable people who generally aren't in a position to lobby for themselves."
AUT head of midwifery Judith McAra-Couper said there was plenty of training about mental health problems, both in theory and in practice.
Rather than knowledge, she believed the problem was the ability to get help when trying to refer women to maternal mental health services.
"This is an area where midwives felt they were often left literally holding the baby.
"They have to plug gaps between the woman and the service, and to ensure the woman's wellbeing.
"The midwives end up being there for them, and trying to support them."
While mothers with acute mental health symptoms could get help, those suffering at a mild to moderate level often ran into a roadblock.
"This is not our specialty. We will support the woman, but we need the woman in an appropriate service from the maternal mental health team," McAra-Couper said.
"We need to look at investing in those in a way that women can get access to the services they need.
"That would be a huge relief for midwives, if there was ready access."
The Maternal Care Action Group currently has a petition appealing for perinatal depression and anxiety to be a priority in this year's budget.
Perinatal depression
Perinatal depression refers to depressive symptoms experienced before, during and after pregnancy.
It combines the terms some people are more familiar with, of prenatal and postpartum depression.
According to Perinatal Anxiety and Depression Aotearoa, 25 per cent of women suffer from depression during or after pregnancy.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• If it is an emergency and you feel like you or someone else is at risk, call 111.
