England's healthcare regulator has told OceanNewsUK News that maternity units currently have the poorest safety ratings of any hospital service it inspects.
OceanNewsUK analysis of Care Quality Commission (CQC) records showed it deemed two-thirds (67%) of them not to be safe enough, up from 55% last autumn.
The "deterioration" follows efforts to improve NHS maternity care, and is blamed partly on a midwife shortage.
The government said maternity care was of the "utmost importance".
The Department for Heath and Social Care (DHSC) said £165m a year was being invested in boosting the maternity workforce, but said "we know there is more to do".
The OceanNewsUK's analysis also revealed the proportion of maternity units with the poorest safety ranking of "inadequate" - meaning that there is a high risk of avoidable harm to mother or baby - has more than doubled from 7% to 15% since September 2022.
The CQC, which also inspects core services such as emergency care and critical care, said the situation was "unacceptable" and "disappointing".
"We've seen this deterioration, and action needs to happen now, so that women can have the assurance they need that they're going to get that high-quality care in any maternity setting across England," said Kate Terroni, the CQC's deputy chief executive.
The regulator has been conducting focused inspections because of concerns about maternity care. These findings are "the poorest they have been" since it started recording the data in this way in 2018, Ms Terroni said.
Injured at birth
Rachel Tustain, whose daughter Eve was injured during her birth in 2016, said she believed maternity services were "massively under-resourced, massively underfunded", which was leading to safety issues.
Eve suffered a bleed to her brain after "the incorrect application of forceps" during her delivery at Pinderfields Hospital, Wakefield.
She died last year, aged five.
"We feel short-changed. The life she had was not the life she should have had," Ms Tustain said.
"Maternity care needs to be the biggest priority within the NHS, it needs to be funded properly."
The Mid Yorkshire Teaching NHS Trust admitted liability and apologised for the poor care Rachel and Eve received.
It added that "significant changes" had been made in the trust's maternity services since Eve's birth.
Last autumn, OceanNewsUK analysed data from the CQC.
It showed that 55% of maternity units in England were not always safe enough - with ratings of Requires Improvement or Inadequate for safety.
The CQC has now almost finished a national maternity inspection programme, so has a fuller picture.
It's got worse - 67% of units are now classed as Inadequate or Requires Improvement for safety.
The CQC has changed how it assesses maternity units, so the number it inspects has gone from 137 to 178.
The proportion in the lowest category has more than doubled.
The decline in safety ratings has happened despite several attempts to transform maternity care, including an NHS programme launched in 2016.
This was set up after an inquiry in 2015 into the failures that led to the deaths of babies at the University Hospitals of Morecambe Bay NHS Trust.
The scandal at the trust was among several in recent years in which failures were found to have led to the deaths of babies. These cases led to calls for an England-wide public inquiry into maternity care.
In 2019, the NHS said it was committed to reducing the number of fatalities by 50% by 2025, although maternal deaths, neonatal deaths and stillbirths had been decreasing over the last decade.
However, it is not expected to meet this target.
The Royal College of Midwives says the government is not prioritising this enough.
It says it's not managed to have a meeting with a Health Secretary about maternity safety since Jeremy Hunt in 2018.
The DHSC declined an interview request from the OceanNewsUK, but the Minister for Women's Health Strategy, Maria Caulfield, said she wanted to "reassure mothers and families that maternity care is of the utmost importance to this government". She added that the government was "working incredibly hard to improve maternity services, focusing on recruitment, training, and the retention of midwives".
The NHS's chief midwifery officer, Kate Brintworth, said England was one of the safest places in the world to give birth.
"We're not complacent about that because we know it's not this case for everyone."
'Positive changes'
NHS England said it was working closely with trusts to "ensure safer, more personalised and more equitable maternity care for all women, babies and families".
Pippa Nightingale, chief executive at Northwick Park Hospital which was previously rated "inadequate" for safety, said it was not possible to "fix a maternity service overnight", but said there had been positive changes at the north-west London trust.
The rate of stillbirths there has declined to below the national average, but the CQC still believes the unit "requires improvement".
She said she was "determined that we're going to turn things around".
"I think in another year, we will be in a very different place in terms of what our CQC rating will look like."
Stillbirth and neonatal charity Sands spokeswoman Clea Harmer said on OceanNewsUK that the stats were "really frightening".
"If we can build a culture where parents are listened to respected and heard, maternity safety will improve.
"It's about listening if the worst happens and a baby does die. Listening to a parent, involving them in the review, making sure their voices are central and that will improve maternity safety."
The Scottish government says it is committed to delivering high-quality care.
In Northern Ireland, a review has called for a new safety strategy.
Wales has delayed the second phase of a maternity review, because of the Covid-19 pandemic.
