The Independent Maternity Oversight Panel found major failings in 21 out of 63 cases at two hospitals run by the Cwm Taf Morgannwg University Health Board.
It also found the views of expectant mothers were often ignored by medical staff and they felt they could not share their concerns.
Staff were also criticised for their insensitivity, with one parent telling the authors they were told by staff: “You had best see him now while he’s at his best.”
The cases, which happened between January 2016 and September 2018, took place at the Royal Glamorgan Hospital at Llantrisant and the Prince Charles Hospital in Merthyr Tydfil.
The review was commissioned after the Welsh Government placed maternity services at the Cwm Taf Morgannwg University Health Board into special measures in 2019.
In 37 cases, the review said one or more minor mistakes happened while lessons could be learned from 48 cases.
There were just four cases where the panel found no issues with the care received.
The findings mirror similar concerns found in maternity services in England where regulators have warned more than two fifths of maternity services need to improve on safety.
Critcism of doctors included parents saying their concerns were not taken seriously while another parent said: "(I was) ... consultant-led but never actually met them until I had my baby and they had died."
The review of the 63 cases was broadly similar to the areas of concern identified by the Royal College of Obstetricians and Gynaecologists and the Royal College of Midwives, which led to maternity services being placed in special measures.
Health and social services minister Eluned Morgan said there had been further "incremental progress", but the Covid-19 pandemic had caused an "understandable loss in momentum".
"The clinical findings were mirrored to a significant extent by the experiences shared by the women and families whose care was reviewed," Ms Morgan said.
"Key themes included a failure to listen to women and value their opinions, inappropriate staff attitudes and behaviours and inadequate bereavement support and aftercare.
"Sadly, nothing can change what these women and families experienced, and I am very sorry for that.
"My thoughts are with all the women and families who experienced a stillbirth and are grieving the loss of their child."
The minister said the report would make for "difficult reading" for staff working in maternity services, but said "significant improvements" have been made in the last two years.
The health board welcomed the review and said it was committed to improving maternity services.
Greg Dix, executive director of nursing and midwifery, said: "Losing a baby is tragic for any family, and our sincere and heartfelt condolences go out to all of our families who have lost a child to stillbirth in our health board.
"We will never forget the tragedies suffered by women, their families and our staff, and the learning from these cases is the foundation on which we are building our improvement plans.
"We are committed to being open and honest about what went wrong and how the learning that has been identified is underpinning meaningful improvement.
"We will ensure that we never forget families in the review, and that their experiences will be the legacy that builds a solid foundation for the future."
Russell George, Welsh Conservative shadow health minister, said: "This latest report into the maternity scandal at Cwm Taf makes for harrowing reading and my thoughts go to the mothers and families who went through such tragic circumstances.
"Women facing childbirth have the right to expect high-quality care, and the best chances of delivering a healthy baby, but they were let down and ultimately failed.
"The scale and longevity of this scandal is shocking and it continues to pose many challenging questions for Cwm Taf and its regulatory system, as well as the Labour Government."
Additional reporting by agencies
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies