A hospital was "inappropriately slow" to respond to repeated failings in its maternity wards, a report claims.
A probe found "recurrent safety risks" in 24 cases, including the deaths of three babies and two mothers, at East Kent Hospitals since July 2018.
The Healthcare Safety Investigations Branch (HSIB) first raised concerns in 2018, but found the failings continued.
The trust, which is to be probed over baby deaths in a separate inquiry, has been asked to comment.
The HSIB said it found the following risks recurred in many of the 24 cases:
- A lack of staff trained to read cardiotocograph machines, which are used to monitor foetal heart rate
- Issues with the delivery of "effective and timely resuscitation" of newborns
- A failure to recognise signs that the condition of a mother or baby is deteriorating, leading to missed changes to intervene
- Concerns over the way complicated births were escalated, including a reported "reluctance of midwifery staff to escalate concerns to obstetric and neonatal colleagues"
The safety watchdog met with the trust in December 2018 and raised concerns about the themes that appeared in the first 10 cases. However, it said "investigators continued to observe the same risks occurring with subsequent investigations".
The trust had been "inappropriately slow given the evidence of ongoing patient safety risks and the safety recommendations made," the HSIB report said. There was later "stronger engagement" and measures were put in place to resolve their concerns after senior figures at the trust later became involved, the report said.
The HSIB took responsibility for investigating such concerns in April 2018 and did not look at cases before then, such as that of Harry Richford, whose death in 2017 was found to be "wholly avoidable".
Harry's grandfather Derek Richford said he was "really disappointed" the trust had "failed to learn" from his death.
"The same themes that caused Harry's death have clearly caused other families to lose babies and mothers as well as unknown levels of brain damage," he said.
He said it was "clear from the report that the trust failed to engage appropriately with HSIB".
An independent inquiry is due to begin later this month after up to 15 babies died at the trust's two sites providing maternity services - the William Harvey Hospital in Ashford and the Queen Elizabeth the Queen Mother Hospital in Margate.