The biggest baby boom in 40 years is expected just as maternity cutbacks hit hospitals.
New figures suggest more than 700,000 babies will be born in England this year, which will be the highest number since 1971, according to the Royal College of Midwives.
This year 4,600 more babies were born between January and March than last year, while NHS maternity services are being cut back nationally.
Cathy Warwick, RCM chief executive, said: "The baby boom is restarting with renewed vigour.
"We are already at birth numbers that haven't been seen for at least a couple of generations, probably not in the working life of any midwife practising today.
"Today's midwives simply have never seen anything like it. The demand this is placing on the NHS is enormous."
The average number of births per midwife has worsened recently and RCM estimate the UK is short of 5,150 full-time equivalent midwives.
More than a quarter of UK heads of midwifery told RCM that their budget has been cut in the last 12 months,
In a poll of 2,000 midwives, 89% said they did not feel able to give women all the care and support they need.
Ms Warwick said: "NHS maternity services, especially in England, are on a knife-edge. We have carried shortages for years, but with the number of births going up and up and up. I really believe we are at the limit of what maternity services can safely deliver."