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Hey researchers, bloggers, everyone interested in fertility data! We recently added lots of new data at Our World in Data on fertility rates, ages at childbirth, twin birth rates, birth seasonality, and more. Here's a thread of what you can find on the site! 🧵

Our new data comes from a range of sources including the Human Fertility Database, the UN World Population Prospects, the Human Multiple Births Database, the Human Mortality Database, and more.

First, of course, the total fertility rate — a metric that summarizes birth rates across age groups of women in one particular year. ourworldindata.org/grapher/chil...

The total fertility rate is commonly interpreted as a prediction of how many children women will have on average over their lifetimes. But it doesn't necessarily tell us that. I've written about why in a recent article:

The completed cohort fertility rate. This is a measure of the eventual number of children born per woman by the end of her childbearing years. You can see that it's given by the woman's birth year, and is estimated *after* they complete their childbearing years. ourworldindata.org/grapher/coho...

Are women having fewer children, more likely to have no children, or both? You can explore the data on the share of women who have had a given number of births. We can see that two is the typical number of children in many high-income countries. ourworldindata.org/grapher/shar...

Teenage motherhood can be a health risk to both mothers and babies. How common are births among teenage mothers around the world? How has this changed over time? You can explore the data on the adolescent birth rate here: ourworldindata.org/grapher/adol...

What's the average age of mothers at childbirth? This shows the average age of women giving birth in a particular year. You can see it's between 26 to 32 in most countries. Note that this is the average across all children born, not just the first child. ourworldindata.org/grapher/peri...

We also have the data broken down by birth order (first born, second born, third born, etc.) for some high-income countries in the Human Fertility Database. ourworldindata.org/grapher/peri...

You can also explore this data by the woman's birth year. This shows when women born in a given year had their children. It helps to track generational changes directly. ourworldindata.org/grapher/aver...

Beyond the average, we also have charts on the age distribution of women giving birth! This chart shows, for each year, the age distribution of women giving birth that year. ourworldindata.org/grapher/age-...

You can again alternatively explore this data by women's birth year. This allows you to see clearly how the age at which women gave birth changed for women of different birth cohorts and generations. ourworldindata.org/grapher/coho...

Although the age distribution curves are only available for mostly high-income countries in the Human Fertility Database, you can explore the distribution by age group in this chart for all countries from the UN World Population Prospects. ourworldindata.org/grapher/fert...

You might be interested in the cumulative fertility rate by a given age — that is, how many births are there per woman, if for example, we only look at women up to age 35, or 40? You can explore that data here too, for countries in the Human Fertility Database. ourworldindata.org/grapher/cumu...

On a related note, you may be interested in the absolute number of births by women of different age groups. ourworldindata.org/grapher/birt... Or even the share of births by women of different age groups. ourworldindata.org/grapher/shar...

Or perhaps, the birth rate (the number of births per 1,000 people) in each country? It's worth noting that the denominator is affected by the age structure. ourworldindata.org/grapher/crud...

As populations age & a lower share are in their childbearing years, the birth rate falls even if the number of children per young adult stays constant. That's why the TFR is typically used instead to track changes in childbearing. But birth rates can be useful to understand the population pyramid.

You can also explore data on giving birth to twins. This chart shows the share of deliveries that are twins. A delivery refers to the birth event in which one or more babies are born, whether it’s a single baby or multiple babies (twin or more). ourworldindata.org/grapher/rate...

You can compare the figures easily between countries, to see what share of deliveries involve twins in different countries, or triplets or more. ourworldindata.org/grapher/shar...

And on another topic, did you know that births have a slight seasonal pattern? We have several charts where you can explore these patterns by looking at the number of births per day in each month and how that's changed over time. ourworldindata.org/grapher/birt... ourworldindata.org/grapher/mont...

In the same chart above, you can explore how that's changed over time. As I've written about, the seasonal pattern of births has shifted over time in many countries. You can see that here for France: where spring used to be the most common season for births, but now it is late summer or autumn.

We also have several charts on the use of contraception. This shows the use of modern contraceptive methods, among women who are married or in union. 'Modern contraception' here means hormonal pills, IUDs, condoms, injectibles, implants, sterilization, vaginal barriers, and emergency contraception.

There are also other traditional contraceptive methods — such as timing — that are not shown here.