The nurses' union says it warned Victoria's Department of Health almost two years ago about problems in neonatal care at a Melbourne hospital as more parents come forward questioning why their babies died.
Djerriwarrh Health Services in Bacchus Marsh and Melton is being investigated after the deaths of seven babies in 2013 and 2014 were deemed avoidable.
Australian Nursing and Midwifery Federation (ANMF) Victorian branch secretary Lisa Fitzpatrick says the union wrote to the department and Djerriwarrh management in January 2014 highlighting concerns from midwifery staff.
She said nurses, and possibly some doctors, had spoken up but later left the service, frustrated their concerns weren't heeded.
Increased births at Djerriwarrh were not matched by additional staff or essential equipment, and the service lacked adequate policies and procedures.
"In the past, midwives were ostracised for reporting risk and we know many worked in a culture and intimidation," Ms Fitzpatrick said.
A spokeswoman for Health Minister Jill Hennessy says the Australian Commission on Safety and Quality in Health Care will investigate whether the Department of Health should have picked up these issues earlier.
"Without pre-empting the outcome, clearly there is a need to strengthen the role of central oversight by the department to prevent anything like this happening again," she said.
The seven deaths have been blamed on a series of catastrophic clinical and governance failures at Djerriwarrh.
A review by obstetrics expert Euan Wallace identified a "multi-system failure" but said no one doctor was common to each case.
It found staff couldn't adequately monitor babies' heart rates.
Other women have now come forward with stories of babies that died before these deaths.
Nichole Bink, whose son Liam was born in 2006 at the hospital, died of an undiagnosed heart defect and she wants the investigation into the hospital to examine earlier deaths.
She said her son had a blue face and cold hands for 24 days before he died of a congenital heart defect and his death could have been avoided if staff had not brushed off her concerns.
"It's nearly 10 years and nothing's changed (at the hospital)," Ms Bink told AAP.
"There are major signs and symptoms that he had that were brushed off."
She consulted a cardiologist at the Royal Children's Hospital to see if she had a genetic problem after Liam died, but learnt he was born with a fixable heart defect.
"He basically turned around and said to me: `It's a 15-minute operation and it has a 99 per cent success rate'," Ms Bink said.
The government has established a support line for anyone concerned about their maternity care at Djerriwarrh.
