According to data from the Office for National Statistics (ONS) covering England and Wales in 2017 – the most recent years for which figures are available – there were 395,856 pregnancies among women in their 20s and 398,284 among women aged over 30.
For the second year running, women aged 40 and over were the only group to see an increase in their pregnancy rate, rising 2.6 per cent.
The ONS credits this with factors including women's increased participation in higher education and employment, rising opportunity costs of childbearing, and housing.
While the rate of pregnancy in women aged under 20 years continued to decrease in 2017 by the 3.8 per cent from the previous year, marking the smallest decrease for this age group since 2008.
But a representative from the sexual health charity Family Planning Association (FPA) suggests the disparity between the age groups may also come as a result of issues surrounding maternity pay for younger generations.
"Maternity pay is complicated by insecure employment considering that you usually need to be employed for a year before becoming eligible," an FPA spokesperson tells The Independent.
"This could apply across the 'gig economy' with self-employment, freelancing and contracted work becoming more common."
The spokesperson added that a lack of resources to support younger families, such as affordable childcare, "could also make the decision to have children at a younger age more difficult".
"However, with shifting attitudes, it’s also possible that many people simply feel less pressure or desire to start a family," they noted.
In an a report published by the Trades Union Congress in 2017, the UK was found to be the third worst ranking country in Europe in terms of paid parental leave.
The ONS figures – which only account for conceptions and abortions, not whether pregnancies end in birth or miscarriages – also show that the number of teenage pregnancies in 2017 decreased for the 10th year running, with almost 18 teenagers aged 15 to 17 out every 1,000 becoming pregnant.
In addition, the estimated number of pregnancies of women aged under 16 fell to 2,517 in 2017, compared with 2,821 in 2016, a decrease of 10.8 per cent.
Improved sex and relationship education, better access to contraceptives and increased participation in higher education were noted to be possible causes for the decrease, according to the ONS.
The news comes months after the education secretary Damian Hinds said children from the age of 15 will be able to opt into sex education classes against the wishes of their parents from 2020.
Women aged under 16 years were the only age group where the percentage of pregnancies leading to a legal abortion decreased from 2016. Despite the decrease, the percentage of legal abortions for women in this age bracket remained higher than all other age groups.
Last week, health watchdog the National Institute of Health and Clinical Excellence (NICE) published new draft guidelines to make it easier for women to access abortion services and have greater choice.
The guidelines, which were developed with the Royal College of Obstetricians and Gynaecologists (RCOG), state that women should be given the choice of a medical or surgical abortion, be able to refer themselves to have their pregnancy terminated, and be given an appointment with a week of requesting one.