The Health and Disability Commissioner has faulted the care given by an independent midwife.
Commissioner Anthony Hill says the midwife failed to recognise and do the right thing when her client became unwell late in the pregnancy.
Mr Hill said in a report released on Monday that the woman became unwell when she was 37 weeks pregnant and contacted her midwife because she was vomiting.
The unnamed midwife thought it was a tummy bug and did not visit her client or get a routine urine test done.
The woman's condition worsened and she saw a family doctor who suspected the potentially serious condition pre-eclampsia.
The family doctor sent the woman for urgent blood tests.
The woman ended up having her first baby by emergency Caesarian.
Mr Hill says the midwife was the lead carer and should have acted sooner.