Record numbers of births to older mothers are putting maternity units under pressure - with the NHS short of around 2,600 midwives, a report has found.
The number of babies born in England and Wales to women in their thirties and forties was up 6,859 in 2014, according to the state of maternity services report 2015 from the Royal College of Midwives (RCM).
Births to women in their early thirties (30-34) have been above 200,000 in each year since 2010 - a level not seen since at least the 1930s.
In every year since 2006, more than 110,000 babies have been born to women in their late thirties (35-39). This is a level of births not seen since just after the Second World War, and four times the level of the late 1970s (1977: 25,527), the RCM said.
For women in their forties, births have been above 29,000 for four years in a row. These are again numbers not seen since the years after the Second World War, and are almost five times the level of the late 1970s (1977: 5,988).
With 661,496 babies born in England last year, almost 100,000 higher than in 2001, the RCM said the NHS is short of around 2,600 midwives, made worse by the ageing of the midwifery workforce.
The number of midwives in England aged 50 or over has doubled from 4,057 in 2001 to 8,169 in 2014.
Last year is believed to be the first year on record when the NHS employed more than 1,000 (1,014) midwives in their sixties.
The number aged 65 or over rose from just eight in 2001 to 177 last year, the RCM said.
RCM chief executive, Cathy Warwick, said: "All women deserve the very best care, regardless of the age at which they give birth. Women have every right to give birth later in life, and we support that. But typically, older women will require more care during pregnancy, and that means more midwives are needed.
"It is deeply frustrating for midwives that they cannot provide the quality of maternity care that they want to deliver because they are so short-staffed."
She added: "What worries me in particular is the retirement time bomb that our report unearths. Not only in England, but across the UK, we are not seeing enough new midwives being taken on.
"Many older midwives will, of course, be very experienced, and they are able to mentor and support newer, younger midwives. But they won't be around in the maternity units forever."
There have been more than 1,100 births to women aged 40 or over in Wales each year since 2010 - and this is the highest levels since the sixties.
There were 148 births in Scotland last year to women aged 45 or above and this represents a fivefold increase since 2000.
One of the report's key findings is that the average age of maternity staff in Scotland has increased significantly - the percentage of staff aged 50 or has risen from 32% of the workforce in 2011 to 42% in 2014.
Northern Ireland has seen fewer births to women and girls under the age of 20 and this is reflective of a similar story right across the UK.
Last year, 839 babies where born to women aged 20 and younger and that is almost half of what it was in 1999 (1,791).
The age profile of mothers has increased by 22% since 2001, while the share of all births to women in their forties has doubled since that period also.
Anna Bradley, chair of Healthwatch England, said: "Giving birth is a rare and special experience for new mothers. It is also one of life's few planned and predictable instances of healthcare, so something all services should be getting right."
She said many women do not feel involved in their care, adding: "What's just as concerning is we know that over half of women who have used a maternity service are ready and willing to give their views and feedback in order to help improve and shape future services, but seven in 10 do not know how to.
"This is indicative of a healthcare system that is not listening to people in order to learn from mistakes, make changes and improve the experience of thousands of women who give birth."