The number of cases uncovered by a maternity review at hospitals in Shropshire has more than doubled.
In April 2017, then Health Secretary Jeremy Hunt announced an investigation into avoidable baby deaths at SaTH, which runs Royal Shrewsbury Hospital and Telford’s Princess Royal.
NHS Improvement has found more than 300 new cases of concern at the trust.
Both NHSI and the Trust have been asked to comment.
BBC Social Affairs Correspondent Michael Buchanan said the new cases were understood to include still births and deaths of babies in the final stages of labour.
They have come to light when NHSI asked SaTh for details on all cases of potential errors after the Department of Health ordered a review.
The independent maternity review is already investigating 250 cases.
The review, being led by midwife Donna Ockenden, initially focused on 23 cases in which maternity failings were alleged.
By March, 250 families had come forward, although it is understood not all the cases related to death or serious harm.
The trust, which was put into special measures in November, was also made subject to “further urgent action” in May amid safety concerns over emergency and maternity services, following an inspection by the Care Quality Commission (CQC).
Rhiannon Davies, whose baby Kate died in 2009 said she was “shocked but not surprised” by the increase in numbers.
“The Ockenden Review team continues to have my full support and needs to be given full and public support from the Department of Health down,” she said.
“Whilst any increase in numbers will likely result in another delay to the official findings of the review, I am prepared to wait – because this has to be done once and done properly for the sake of everyone affected.”
By BBC Social Affairs Correspondent Michael Buchanan
NHS regulators have had to be dragged to acknowledge the potential scale of failings at this trust.
The original inquiry was instigated by two sets of parents going through newspaper clippings, and forcing the then health secretary to recognise their concerns and set up what has become known as the Ockenden Review.
These new cases were uncovered after NHSI finally put pressure on the trust last autumn to open up its books, rather than relying on families to highlight their own cases.
However, they didn’t turn the screw until more than 18 months after Jeremy Hunt asked regulators to investigate the problems.
Not everyone whose case is being highlighted will have been failed.
But there was clearly a cultural problem at this trust, spanning more than a decade, that allowed far too many errors to be committed, allowed healthy babies to die or to be harmed unnecessarily.
The potential scale of those mistakes is now, perhaps finally, being revealed.
Follow BBC West Midlands on Facebook, on Twitter, and sign up for local news updates direct to your phone.