Women over 40 are having more babies than the under 20s for the first time in nearly 70 years, official figures for England and Wales show.
The Office for National Statistics data showed there were 697,852 live births in 2015.
There were 15.2 births per 1,000 women aged over 40, compared with just 14.5 per 1,000 women in their teens.
The last time the over 40s had the higher fertility rate was in 1947, in the wake of WWII.
According to BBC, the figures show two key trends in who is having children and when in England and Wales.
The teenage pregnancy rate has been in long-term decline and has more than halved from the 33 births per 1,000 teenagers in 1990.
Meanwhile, pregnancies have soared in older age groups from 5.3 per 1,000 in 1990.
The average age of having a child is now 30.3 – a figure that has been increasing since 1975.
Advances in fertility treatment as well as more women in higher education and attitudes around the importance of a career and the rising costs of childbearing are behind the rise, the ONS says.
Liz McLaren, head of vital statistics outputs at the ONS, said: “The trend for women to have babies at older ages continued in 2015.
“Over the last 40 years, the percentage of live births to women aged 35 and over has increased considerably.
“Women aged 40 and over now have a higher fertility rate than women aged under 20 – this was last recorded in the 1940s.”
The data also shows that fertility rates have dropped in all age groups under 25 while increasing for all age groups 30 and over.
Women aged between 30 and 34 have the highest fertility of any age group – with 111 births per 1,000 women.
The number of births to women born outside the UK has also continued its rise, reaching 27.5 per cent of all births.
Prof Adam Balen, the chairman of the British Fertility Society, said: “We know that female fertility starts to decline gradually from the late 20s and more rapidly from the mid-30s onwards.
“While the risks should never be overplayed, men and women should be aware that reproductive outcomes are poorer in older women.
“As well as it potentially taking longer to get pregnant, later maternity can involve a greater risk of miscarriage, a more complicated labour, and medical intervention at the birth.”
The British Pregnancy Advisory Service said: “The trend towards older motherhood is here to stay, and there are many understandable reasons why women today are waiting longer to start or expand their families than those in previous decades.
“Rather than bemoaning this development, we should seek to understand and support the decisions women make.
“More affordable childcare and improved maternity rights may make it easier for some women to start their families earlier if they wish, but we also need to ensure we have high quality reproductive healthcare services configured to meet women’s needs, whatever the age at which they conceive.”