Expectant mums were turned away from closed maternity wards hundreds of times last year, according to hospital figures.
More than 40 per cent of maternity wards in England closed at least once in 2016, according to the data released by the Labour Party.
It found 42 out of 96 trusts said they had shut temporarily 382 times.
The most commons reasons were short staffing and not enough beds.
Forty of the 136 hospital trusts in England did not respond to requests for information.
Among those that did was the Royal Berkshire NHS Foundation Trust, which closed its maternity unit 30 times in 2016, citing “insufficient midwifery staffing for workload”.
Mid Yorkshire Hospitals NHS Trust closed its unit five times, once for 14.5 hours to “maintain safety and staffing levels”.
East Cheshire NHS Trust closed its maternity unit for eight hours, citing “full cot occupancy” in the neo-natal unit.
Bradford Teaching Hospitals NHS Foundation Trust closed its maternity unit 10 times, because of capacity, high activity and staffing.
Shadow health secretary Jonathan Ashworth said: “These findings show the devastating impact which Tory underfunding is having for mothers and children across the country.
“The uncertainty for so many women just when they need the NHS most is unthinkable.”
Sean O’Sullivan, from the Royal College of Midwives, said there was a shortage of 3,500 full-time midwives.
He added: “If units are regularly and persistently having to close their doors, it suggests there is an underlying problem around capacity and staffing levels that needs immediate attention.”
A Department of Health spokesperson said there were now more than 2,000 additional midwives compared with May 2010.
There are also 6,500 midwives currently in training.
“Temporary closures in NHS maternity units are well rehearsed safety measures, which we expect trusts to use to safely manage peaks in admissions,” the spokesman said.
“To use these figures as an indication of safe staffing issues, particularly when a number of them could have been for a matter of hours, is misleading because maternity services are unable to plan the exact time and place of birth for all women in their care.”
I had both my babies at the Royal Berkshire Hospital in Reading. I found their staff to be amazing, I can’t praise them enough.
But I was very lucky to deliver there with my first baby. Just 30 minutes after we arrived in 2015 the delivery ward was closed.
I remember hearing an expectant dad rage at staff in the reception area because he had been told he had to take his pregnant wife to Oxford.
Labour is one of the hardest things you will ever go through. I hope more funding and career support is found for midwives. They are absolute heroes.