Dr Vanessa Purday, the trust’s chief medical officer, said it was “deeply disappointing” not to be able to reopen the unit.
She said: “Whilst we’ve made good progress and we have recruited to both our consultant and registrar voters.
“We don’t have the numbers of doctors we need to do reopen safely and keep the service open safely.
“We also need to make sure that for those doctors who have joined us are able to complete all the on-boarding checks that we need to do to make sure that they can meet the requirements of the role.”
She said the 29 September date was “always conditional” on final staffing and safety assurances, adding it “remains safer” to keep the suspension in place.
“This is not a decision to permanently close birthing services at NDDH,” she added.
“We remain fully committed to reopening the service and will continue to be open and transparent about our progress, the challenges we face and the steps we’re taking to address them.”