Women who have delayed having babies until their 30s now outnumber younger mothers for the first time.
New figures have revealed that more than half of babies in England and Wales are now being born to women aged at least 30 years old.
The Office for National Statistics (ONS) showed that just over 50 per cent of the 698,512 children born last year had mothers who were 30 or older - the first time since since records began in 1938.
Only 21 per cent of babies born last year had a mother under the age of 25, while those over 35 accounted for 20 per cent.
The gap between the two groups has narrowed dramatically in the last year alone, falling from a difference of more than 21,000 more younger mothers in 2012 to just 8,000 more in 2013.
Just 20 years ago younger mothers outnumbered those over 35 three to one. Last year 29,158 women over 40 had babies.
The trend suggests the number of middle aged women giving birth will overtake those under 25 within the next few years.
The ONS said: "The overall rise reflects the increasing numbers of women who have been delaying childbearing to later ages."
Statisticians said possible influences include: increased participation in higher education; increased female participation in the labour force; the increasing importance of a career; job market uncertainty; housing issues and instability of partnerships.
Another factor could be the growth in fertility treatment.
Some companies – such as Apple and Facebook – even offer career women cash incentives of £12,600 to freeze their eggs to delay starting a family.