More than 900 families have now contacted an inquiry into the maternity scandal at hospitals in Shropshire.
The review, led by Donna Ockenden, is focusing on claims that patients died or were harmed in the care of Shrewsbury and Telford Hospital Trust.
On Wednesday, the House of Commons heard that the "huge increase" from the 23 cases originally identified was "shocking".
In November it was revealed investigators were examining 800 cases.
The trust, which runs Royal Shrewsbury Hospital and Telford Princess Royal, said in a statement it was glad an appeal to families by Ms Ockenden in 2019 "appeared to have had the desired effect".
It added it was "truly sorry" and that it was committed to working with the Ockenden review.
Wednesday's Commons debate was called by Telford MP Lucy Allan, who compared the time taken to complete the Ockenden review to the Morecambe Bay inquiry in to baby deaths, which "reported promptly".
Health Minister Nadine Dorries replied to say the original scope of the investigation had been expanded and some of the cases identified dated back 40 years.
"Nine hundred cases in terms of a review will take considerably longer in terms of time. And that is why there has been no report so far," said Ms Dorries.
Former health secretary Jeremy Hunt, who commissioned the review in 2017, said the surge in numbers was "deeply shocking" and compared it to hospital failings which led to hundreds of deaths in Staffordshire .
"She [Ms Dorries] is saying that the scale of potential avoidable death at Shrewsbury and Telford may in fact be no different to mid-Staffs," said Mr Hunt.
Maternity expert Dr Bill Kirkup, who headed the inquiry into baby deaths in Morecombe Bay, has previously raised concerns the Shropshire case points to "underlying systemic failure" in the NHS.
The Ockenden review is expected to conclude at the end of the year.
Follow BBC West Midlands on Facebook, on Twitter, and sign up for local news updates direct to your phone.