More babies have been born to women 35 and over than to those under 25 for the first time.

Newborns to mothers aged at least 35 accounted for 21% of births in England and Wales last year, compared with 20% to those under 25, , according to data from the Office for National Statistics (ONS).

There were 138,592 live births to women under 25 and 144,181 to women 35 and over. There were three times as many births to mothers aged 25 to 34 than to those under 25.

Dr David Richmond, president of the Royal College of Obstetricians and Gynaecologists (RCOG),said: “It’s undeniable that the age in which women are having their first baby has increased over the past few decades, due to a variety of social, professional and financial factors.”

The trend of later parenthood is unlikely to be reversed dramatically, he said. “But it’s important that both men and women are aware that fertility starts to decline from the mid-30s onwards.”

He added: “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.”

Richmond said the RCOG supported initiatives to help educate young people about the optimum age to start a family. “More could also be done as a society to support women who would like to start a family earlier. For example, maternity pay, job security, access to flexible working and the cost of childcare are all prohibitive factors,” he said.

Fathers tend to be older than mothers, the ONS figures for England and Wales show. Last year two-thirds of babies had fathers aged 30 or over.

The average age of all fathers increased to 33.1 in 2014, from 32.9 the previous year. For mothers, the average age was 30.2, compared with 30 in the previous year. The average age of first-time mothers was 28.5 in 2014, up slightly from 28.3 in 2013.

The number of births to women in their forties was above 29,000 for a fourth year in a row – a pattern not seen since the years after the second world war. The number of babies born to women aged 20 and younger was almost half of what it was in 1999, at 839 last year.

The majority of births (53% last year) were to couples who were married or in a civil partnership, compared with 58% in 2004 and 93% in 1964.

A recent report from the Royal College of Midwives said the NHS was short of about 2,600 midwives as record numbers of births to older mothers were putting maternity units under pressure.