Maternity services at Cwm Taf Morgannwg University Health Board have been placed into special measures, after an external review identified "serious failings".
The review of maternity services was commissioned by the Welsh Government after concerns were raised surrounding the number of deaths of babies in its maternity units.
In October last year, the health board said 43 cases at Prince Charles Hospital in Merthyr Tydfil and Royal Glamorgan hospital in Llantrisant were being reviewed.
The cases included 20 still births and six neonatal deaths between 1st January 2016 and the end of September 2018 and where there was an "adverse outcome" to mothers or their babies.
In a statement, Health Minister Vaughan Gething said the report makes for "difficult reading" and apologised to all families affected.
Following the publication of the findings, he confirmed cases as far back as 2010 will be looked at.
Midwives were described as being under "extreme pressure" and were working due to a "longstanding shortfall in staffing". They were repeatedly described as being at "breaking point".
The report makes very difficult reading. I would like to start by apologising to the women and families affected by the poor standard of care described.
Chief Medical Officer Dr Frank Atherton described it as a "difficult day".
The report was led by the Royal Colleges of Obstetricians and Gynaecologists which included a team of experts in midwifery, obstetrics and neonatal care. The team visited the hospitals between 15-17 January 2019 and spoke with families and staff - and identified a number of "immediate quality and safety concerns".
The Minister announced that maternity services at the health board - formerly known as Cwm Taf University Health Board - have now been placed in the highest level of escalation.
Some of the immediate concerns highlighted in the report included the lack of availability of consultants.
"Although cover is shown on rota schedules, there is often no actual presence and difficulty in making contact."
Other concerns included inadequate support for trainee doctors, lack of a "functioning governance" and unacceptable levels of midwifery staffing levels. The report found ''significant issues relating to staffing of the maternity unit within all professional groups at all levels.''
Assessors also found a number of ''inappropriate, undermining and unprofessional behaviours'' by some midwives.
Patients who raised concerns ''repeatedly stated'' they were not listened to and concerns were ''not taken seriously or valued.'' Many women said communication was poor with a ''lack of kindness and empathy in sharing bad news or that a pregnancy was at risk.''
Support after the loss of a baby varied, according to the report. It found gaps in provision with many women and families receiving no bereavement counselling or support.
In an interview with ITV News, Health Minister Vaughan Gething said "cultural change is required" across the health board - not job losses.
"The buck stops and starts with everyone involved in the health service doing what they could and should do. That's about the board... about people who deliver the service. I just think the focus on saying someone needs to be sacked is not the right thing to do".
As part of the increased arrangements, the Minister announced an independent panel will oversee services led by the former chairman of the Welsh Ambulance Service Mick Giannasi.
Cwm Taf University Health Board issued a public apology for the failings identified in the report. In a statement, the health board said they ''fully accepted'' the findings of the review and rectifying the issues raised is now their ''utmost priority.''
The health board said it had been working hard to make improvements after feedback by the review team in January, but ''significant work remains to be done.''
Chief Executive of Cwm Taf Morgannwg, Allison Williams, apologised to the women and families affected by the failings.
I am deeply sorry for the failings that have been identified in our maternity service. Every woman deserves to be treated with dignity and respect, safe in the knowledge that they will receive the very best care at this important and vulnerable time in their life.
Speaking on Wales at Six, the Chief Executive said she would not resign over the findings.