Parents involved in the inquiry, which is investigating more than 1,800 cases of poor care at Shrewsbury & Telford Hospital NHS Trust (SaTH), have been told the final report will now be published in March.
The review into what is the country's largest ever maternity scandal had been expected to publish its findings in December.
In a letter to parents involved in the inquiry, which is being led by maternity expert Donna Ockenden, she explains that "a very substantial amount of information" relating to the investigation had been discovered during the summer.
Ms Ockenden had subsequently requested a delay to the publication of the report from the Health Secretary Sajid Javid, which has been granted.
The Shropshire Star understands that extra records, which included details relevant to a large number of cases, had been discovered at SaTH over the summer.
The first stage of Ms Ockenden's report, looking at the findings from around 250 cases, was published last year.
It revealed harrowing details of the experiences of those involved – dating from 2000 to 2018, including the original 23 cases which led to the government launching the inquiry back in 2017.
The review has also led to West Mercia Police launching a criminal investigation into maternity care at the trust, named Operation Lincoln.
In her letter to parents Ms Ockenden said the delay was needed to "thoroughly review" the new information
She said: "My team and I have been working hard towards this and I hoped that the second report would launch at the end of this year.
"However, over the summer months and right up to the end of September we were provided with a very substantial amount of information that was important to us and the review of family cases.
"One we were able to consider the information, my team all agreed these documents were too important to put to one side. Therefore, we wrote to the Secretary of State for Health and Social Care, the Rt Hon Sajid Javid MP to ask for more time to thoroughly review this new information.
"My team and I all believe this was absolutely the right thing to do."
Responding to the announcement Hayley Flavell, director of nursing at Shrewsbury & Telford Hospital NHS Trust, said: "We note the new publication timescale and will continue to co-operate fully and openly with Donna Ockenden and her team, as we have since the review was first launched.
"Alongside this we will continue in our work to implement in full the measures set out in the first report where we have made strong progress and have already completed over 60 per cent of the actions, and we will address any new actions raised in the final report with the same focus and resolve we have brought to the initial recommendations."
Rhiannon Davies, who along with Kayleigh Griffiths, wrote to Jeremy Hunt back in 2017 outlining their concerns over the trust, leading to the launch of the inquiry, said they wanted to know how the files had been discovered.
She said: "When Kayleigh, Colin, Richard and I learned, earlier this month from a journalist, that hundreds of case files had apparently been discovered at SaTH we wrote to Sajid Javid and Jeremy Hunt asking how this could have happened. We also insisted that the Ockenden team be given any additional time needed to comprehensively review these files."
She added: "This is a once in a generation opportunity for comprehensive learning for the prevention of future avoidable deaths – it has to be done once and done right. It has come about at huge personal cost for 1862 families. That fact must never be forgotten."
Ms Davies said she welcomed the extra time allowed to review the files and called on the Information Commissioner’s Office to look at the case.