- Video report by ITV News Political Correspondent Carl Dinnen
More than four in ten maternity wards were forced to temporarily close their doors to new arrivals last year, according to new data obtained by Labour.
Dozens of NHS trusts in England said they had been forced to turn away expectant mothers due to shortages in beds or staff.
In total, the report found English hospitals had to temporarily refuse new arrivals to their maternity wards to new arrivals on 382 occasions in 2016.
That is an increase on the 375 times in 2015 and 225 occasions in 2014, Labour said.
One hospital reported it had to temporarily close its maternity ward 30 times within a year due to having insufficient staff.
Shadow health secretary Jonathan Ashworth said the "staggering" figures revealed the "devastating impact" of insufficient NHS funding.
"The uncertainty for so many women just when they need the NHS most is unthinkable," he said.
"It's shameful that pregnant women are being turned away due to staff shortages, and shortages of beds and cots in maternity units."
Labour obtained the data through a freedom of information request to 136 hospital trusts with maternity units in England.
Of the 96 trusts that responded, 42 trusts (44%) said they had temporarily closed their doors on at least one occasion in 2016.
In most cases, lack of capacity issues and staff shortages was the main issue.
Midwifery leaders called for action to tackle "significant pressures" on maternity services across England, which face a shortage of around 3,500 full-time midwives.
Sean O'Sullivan, head of health and social policy at the Royal College of Midwives(RCM), said the latest figures came as "no surprise".
He said: "The RCM has warned time and time again that persistent understaffing does compromise safety and it's about time the Government listened to those best placed to advise."
Mr O'Sullivan said the RCM supported the decision to refuse new admissions when taking on more patients would compromise safety.
However, repeated closures suggested problems with capacity and staffing that require "immediate attention", he added.
A spokeswoman for the Department of Health said there were "enough midwives in the NHS".
"Temporary closures in NHS maternity units are well rehearsed safety measures which we expect trusts to use to safely manage peaks in admissions," she 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."