WS MoreOrLess: Fertility - when is too late?
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What is the main topic discussed in this episode?
This is the short edition of More or Less, first broadcast on the BBC World Service.
Hello, and welcome to More or Less on the BBC World Service, the programme which smites the dragon of dodgy data with the shining sword of statistical straight-talking. I'm Tim Harford. The comedian Tina Fey has been looking at her magazine collection.
The cover story of New York Magazine this week is Baby Panic. This goes perfectly with the other magazines on my coffee table, Where Are the Babies?, Why Haven't You Had a Baby?, and For God's Sake, Have a Baby!.
That's from the US show Saturday Night Live back in 2002. It is, of course, possible that some of those headlines weren't genuine, but this one is. Have babies by age 35, say experts. And so is this one.
Pregnancy after 35 is like an Iron Man challenge.
Let me tell you the story of Jean Twenge, a professor of psychology at San Diego University. Back when that edition of Saturday Night Live went out, Jean was having a tough time. She was 30 years old and on the verge of a divorce. A few years later, she had found love again. Hurrah! But Jean and her new husband wanted to have children, and panic quickly set in.
I read a lot of very scary statistics.
And one in particular made her feel pretty desperate.
One out of three women over the age of 35 will not be able to get pregnant within a year.
So that means that after 12 months of trying to conceive naturally, only two-thirds of women will have been successful. But Jean was determined to find out more. Where had that figure come from?
The data on which that statistic is based is from birth records from 1700s France.
1700s France.
Yeah, yeah. I mean, 1680 to 1810 or something like that.
We're talking about women who have never seen an electric light bulb, no antibiotics, no modern health care. I mean, it's quite extraordinary that that's where the data is coming from.
What common “baby panic” headlines are being challenged in this episode?
Well, you know, I can empathize slightly with the researchers in this area because It is difficult to draw conclusions about age and fertility from modern populations where birth control is widely used.
But surely there are some more modern studies. In her statistical search, Jean then came across a paper by David Dunson at Duke University in the US.
It was published in 2004, and it found that women over 35 had a much higher chance of getting pregnant than those historic birth records would suggest. It found 82% got pregnant within a year. What was really interesting is that wasn't all that different from women in their late 20s and early 30s, where the figure was 86%.
So to put that another way, instead of one in three women in their late 30s not being pregnant after a year of trying, this study said that fewer than one in five women would be in that position. And of the women who did have trouble conceiving, many of them would have had trouble even if they'd started trying earlier on. Now, our reporter Hannah Barnes is with me now. And Hannah, Jean was looking at data and statistics widely quoted in the United States.
Yeah, and similar stats are quoted elsewhere too. The question is, do the experts back her up? And they do. I've been talking to David James from the National Institute for Health and Care Excellence in the UK. He said the Dunson study was far more reliable than studies which use historic data and that the Dunson numbers are the ones which modern couples trying to conceive should be looking at.
It was a single study undertaken relatively recently that of about 780 women in seven different European centers. And the important point about that was that these were women who were trying to conceive. The other study, which produced these very pessimistic figures for chances of success, were actually merely reporting the reproductive performance in a group of women over many centuries without the same criteria of intending to get pregnancy. So in other words, this was a report which should not have been used to form the basis of saying what is the chance of a woman conceiving at age whatever.
And of course, they could have actively been trying to avoid getting pregnant.
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Chapters
4 chapters
1
What is the main topic discussed in this episode?
0:00–2:13
2
What common “baby panic” headlines are being challenged in this episode?
2:13–5:27
3
How did Jean Twenge discover the origin of the ‘one in three over 35’ fertility stat?
5:27–8:46
4
Why are 18th‑ and 19th‑century French birth records a poor basis for modern fertility advice?
8:46–9:32