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."
Student midwife numbers are also being cut and student bursaries for midwives are being cut by £890 in Northern Ireland.
Newly-qualified midwives are struggling to find jobs and a third of new midwives are unemployed.
Of these, almost a half (47%) have been looking for a job for more than three months.
Ms Warwick added: "What is so frustrating is that there is a clear need for more midwives. We have record-breaking birth figures and we need all the midwives we can get.
"We're training midwives, but we're not recruiting them. That is a sad waste of all their time and effort, and a waste of taxpayers' money too."
Several maternity units have closed this year, including three birth centres in the East Midlands and units in Canterbury and Dover.
Ms Warwick said: "The units that have closed are the tip of the iceberg. A 10th of the heads of midwifery who responded to our recent survey told us that they have a midwife-led unit in their area that is in danger of closure."