New mothers who need psychiatric care are travelling up to 10 hours to be hospitalised in England because there is no suitable facility in Wales, the author of a new report has said.
Plans for a specialist unit have been under consideration since July 2017 but no decision has been made.
Dr Sarah Witcombe-Hayes, who led the research, said a Welsh facility was vital.
The Welsh Government said it was exploring options for the service.
Wales' last specialist mother and baby unit closed in Cardiff in 2013 and campaigners have been calling for a new unit ever since.
Dr Witcombe-Hayes, who works for NSPCC Cymru, said: "Having to access mother and baby provision in England has quite a detrimental impact both on women and their families.
"Women in the research told us they were either having to travel very far to access these specialist provisions - Nottingham, Derby, Staffordshire, London, sometimes a seven to 10 hour journey when a woman is so acutely unwell - or they were being treated in inpatient psychiatric units within Wales without their baby and no space for their partner of baby to visit.
"[This] had emotional impacts on women and their families.
"It is vital that Wales has provision for a mother and baby unit for women experiencing the most severe conditions."
The report, From bumps to babies: Perinatal mental health care in Wales, heard from 69 women with experience of perinatal mental health issues and 45 professionals.
One woman who was treated on a psychiatric unit in Wales told researchers: "I was not in an appropriate environment... there was absolutely no provision for my partner and son to visit during the day.
"They weren't allowed to come to my room, we used to spend the time wandering the hospital corridors."
'Where's my baby?'
Sarah Hayes, 47, from Wrexham, was over the moon when her son was born.
"I looked at my beautiful baby and could not believe he was mine," she said.
But she found she could not sleep: "Instead of sleeping when I had the chance I was writing poems in the middle of the night. I also phoned my gran to tell her how much I loved her at about 4am."
When her son was six days old she was facing another sleepless night so put the TV on to try and relax: "The early morning news was on the television and I saw myself and my family on the news as clear as anything.
"The news reader told the story of a girl who won the lottery and didn't know she had won. There was a photo of me and my family with my son the day he was born.
"The newsreader went on to say that someone put my numbers on for me when I went into labour and I won but did not know I had won."
She called her mother and husband who quickly realised something was wrong. An ambulance was called.
The next few weeks are a blur for Ms Hayes. She was admitted to a psychiatric unit without her baby.
"I was asking 'where's my baby?'. I was on mind-numbing drugs and drifted in and out of reality.
"I was terrified and I thought I'd died... I tried not to think certain thoughts as I believed people could see my thoughts."
After three weeks she was able to go home to continue her long, slow recovery.
"I did recover and I have managed to work, bring up my son and have lived a functional life but I still miss the person I was.
"I am closer now than I have ever been to being my old self but it has been a very gradual process.
"I feel really sad that I missed out on those easy days of my son's life."
Her son is now 23 and she is passionate about fighting for improved care and supporting other women who find themselves in her position through the charity Action on Postpartum Psychosis.
"I feel really, really cross because women are losing their lives because they aren't getting the treatment they need."
A perinatal nurse specialist told researchers the difficulties one of her patients faced after being allocated a bed in England.
"It took them 10 hours to get there… it was horrendous because you have to stop with the baby every two hours because it was a new born… they got there at 10pm... what a terrible thing to do to that woman who was psychotic."
The report said important progress has been made in the provision of care following investment from the Welsh Government but also found the area in which a woman lives still determines the level of specialist support she can access.
Six out of Wales' seven health boards have a dedicated perinatal mental health service - Powys Teaching Health Board is the only one that does not.
The report was a joint project between NSPCC, National Centre for Mental Health, Mind Cymru, Mental Health Foundation and supported by the Maternal Mental Health Alliance's Everybody's Business campaign.
A spokesman for the Welsh Government said: "We are committed to improving perinatal mental health services.
"Since 2015 we've invested £1.5m a year in community perinatal mental health services across Wales, which help identify, treat and manage mental ill health before and after childbirth.
"We are exploring options to ensure mothers can receive more intensive and inpatient perinatal support in Wales without being separated unnecessarily from their babies and families."