The woman became pregnant with her third child in early 201, and engaged the midwife, who had also provided maternity care for her during her previous pregnancy.
"I thought I was going crazy to be thinking that my midwife and so-called friend was sleeping with the father of my children"
But, midway through the pregnancy, the midwife ran into her patient's partner at their local shops.
They wound up drinking beer at a nearby park and "engaged in kissing and fondling".
Within weeks a sexual relationship had started.
Speaking with Health and Disability Commissioner Anthony Hill, the patient revealed that she had begun to suspect the relationship towards the end of the pregnancy, but didn't find out until after the baby was born, when she read text messages on her partner's phone.
She said: "The final two months of my pregnancy were horrible.
"I was working, I had two small children and I thought I was going crazy to be thinking that my midwife and so-called friend was sleeping with the father of my children."
She added: "I literally thought I was losing my mind. I was paranoid and in a high state of anxiety.
"I went into shock, I could not believe that two people who were supposed to care for me could possibly be so horrible and act with such disregard."
The midwife, who has been found to have seriously breached the ethical code of midwifery, admitted that she was "embarrassed and ashamed" of her behaviour.
She will no longer work privately as a self-employed midwife, but will work in a hospital and be monitored by a senior colleague for a year.
Stock images used throughout.