The Commissioner said the midwife did not carry out a speculum examination of the woman's cervix or take vaginal swabs during her first assessment of the patient.
The woman had arrived at hospital complaining of abdominal pain.
The midwife failed to perform a speculum examination prior to the woman being transferred to another hospital.
The woman's pain intensified and although the baby was born, it died soon after from complications the premature birth caused.
The midwife, who along with the woman has name suppression, was also found to have not properly documented her assessment findings or her discussions with the woman.
The midwife provided a written apology to the woman and attended a workshop on documentation.
Mr Hill also recommended the midwife undertake more training on how to diagnose pre-term labour.