She died later that night.
Coroner Meenal Duggal is investigating, and the death comes amid concerns about the workplace culture at the intensive care unit.
A statement from Te Whatu Ora MidCentral interim district director Dr Jeff Brown said "the passing of a mother and her baby" were tragic events, and officials were in contact with the woman's whānau.
"A comprehensive clinical review is well under way and recommendations that come out of this review will be implemented as a priority."
Te Whatu Ora declined a request for an interview and did not answer questions about the reason for the delay in admission, nor if the intensive care unit was full on the day of the incident.
Sepsis is considered a preventable cause of maternal death, but Society of Obstetric Medicine of Australia and New Zealand guidelines say prompt treatment is essential.
It is usually caused by a bacterial infection. When the body fights this it leads to damage to tissues and organs.
According to the Perinatal and Maternal Mortality Review Committee, pregnancy-related infections that cause death are rare, with less than one death a year on average.
On average, 10 women a year die during pregnancy or within 42 days of its end.
Meanwhile, RNZ has been told there are concerns about a culture of bullying and intimidation at the Palmerston North intensive care unit.
Earlier this year one staff member launched a survey about this, but management put a stop to it.
Brown said the survey was not authorised by the chief medical officer.
"Many staff were upset by its content and what they felt were leading, unfair questions, and passed on their concerns to the district director and the chief medical officer.
"The survey, including survey questions and any data gathered, was then withdrawn and deleted by the staff member. "
Brown said no staff who had left the unit in the past six months had cited bullying or culture as a reason for their resignation.
"We are unaware of any staff who have left ICU because of this and we encourage all our staff to report any concerns through a variety of pathways, including anonymously. Any reports of bullying are investigated."
RNZ understands there is a feeling among some hospital staff that concerns would not be acted on, and there is a desire to have an external reviewer appointed to run the rule over the unit.