"Some of these women really should have stayed in hospital longer but bed capacity has been insufficient," Knetsch told the Herald.
Under Ministry of Health guidelines, all women had the right to 48 hours' hospital care after giving birth.
Knetsch said the current maternity ward's monthly average capacity was 85 to 90 per cent.
"However, we usually have three to five days each month when the overall capacity on those days is not sufficient," Knetsch said.
"Women have longer wait times to go from birthing and assessment up to a postnatal bed or delays in transfer to one of our primary birthing units for their postnatal stay," Knetsch said.
New Zealand College of Midwives chief executive Alison Eddy said bed availability at maternity wards was a nationwide problem.
"I don't know enough about this proposed ward but I know finding bed space is a constant struggle and certainly having that extra support would help provide better support," Eddy said.
The new ward will be housed in an existing part of the hospital known as Ward 21 until a new Women's Health building is completed in about five years. It will operate in addition to the 45-bed existing maternity ward.
The new ward would primarily be used for antenatal care while the existing ward would become primarily focused on postnatal care with dedicated transitional care
capacity for babies and their mothers and high-risk cases.
Knetsch said part of the growing demand for beds came from a increasing rate of complex births, which meant mothers couldn't deliver at any of the three primary birthing units in Counties Manukau. Those units don't have surgeons or operating theatres.
At a meeting last week, a board member said those rates were "extraordinarily high" and it was a piece of work the DHB would like to take to the Ministry of Health.
Caesarean-sections are also fall into the complex birth category. About 30 per cent of women giving birth at Middlemore Hospital are getting a C-section - 245 more from 2014 to June last year.
Overall births in theatre were up 18 per cent over this time period.
More babies were being born premature, induction of labour was increasing and epidurals were a lot more common, Knetsch said.