The average age that British mothers give birth is now 29.8 years, an all-time high according to the latest data from the Office for National Statistics (ONS). But every year since 2003 has been an 'all-time high' as the average age of motherhood in the UK has continually risen since the 1970s.

There's a tendency to focus on the second half of this chart (the steady rise in the age of motherhood) and attribute it to female economic independence and improvements in family planning - but what about the first half?

The answer, according to a paper from parliament, lies partly with older women:

Fertility among women aged 40-44 peaked in 1947 at 19 births per thousand women in England and Wales. In 2010 the number was 13. In between, fertility among older women declined, reaching a low of four births per thousand women aged 40-44 in 1977.

That's not the only interesting trend in British motherhood which is hidden behind an average. Almost 34,000 babies were born to mothers aged under 20 in 2012, 4.7% of all babies. Of those, a small number were born to very young mothers - 162 by 14 year-olds and just 17 by mothers aged 13 and under. At the other end of the spectrum, just 212 babies were born to mothers aged 49 and over last year.

The average age of parenthood is slightly lower for those in legally recognised partnerships and there are also differs between men and women. The largest number of babies born outside of marriage/civil partnership had mothers aged 20-24 and fathers aged between 20 and 29. For babies born within marriages or civil partnerships, mothers were most likely to be aged 30-34 while fathers were most likely to be aged between 30 and 39.

International trends

The UK might have some of the oldest mothers in the world but it is not the only country to witness a steady rise in the age at which women give birth. In Germany in 1970 the average age of becoming a mum was 24 but by 2009 that had risen to 30. On average, in wealthy OECD countries, women are delaying motherhood four years later than they were in 1970.

Why does that matter? Because there is a correlation between average age of becoming a mother, number of children, employment, education and even women's rights. That doesn't necessarily imply causation (you can debate that in the comments below) but when we collected the data on the average number of children per woman (total fertility rate) and the number of years spent in school it was clear that as one fell, the other increased.

In the chart below, you can select specific countries the click the play button and watch what happens over time. Where the data is available, we've also included the average age of marriage.

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