Nigel Hawkes: Love in a cold climate: Why baby boom is not down to big freeze

Behind The Numbers

Share
Related Topics

If you believe what some newspapers report, last year's winter storms are about to be followed by a blizzard of September births.

The evidence comes from Portsmouth, where the city's midwives expect heaving maternity wards after an unusually large number of 12-week pregnancy scans were carried out in March and April. Six hundred babies are expected to be born there in September – 20 per cent more than usual.

One city doesn't make a national trend, so it would be easy just to dismiss this story. But the way births are distributed across the year is a fascinating subject, and there is indeed evidence that the Christmas holiday has an influence. What is much less plausible is the suggestion that a cold Christmas has us all cuddling up for lack of anything else to do, appealing as it sounds.

In Europe, births peak in early spring and summer, and again in September. In the US, by contrast, births fall in spring, but there is a similar September peak. The pattern is persistent and hard to explain, since the populations share a common genetic inheritance – and Canada follows the European pattern, not the American one.

The differences can be quite large: in England and Wales, about 4 per cent more births are recorded in June and in September/October than in an average month, and 7 per cent fewer in February (a short month, of course).

Parents have a preference for summer births, so these effects are partly driven by conscious choices. But long-run studies have shown that seasonality pre-dated effective contraception. "Through wars, through social upheaval, through government-supported programmes of fertility control, through tremendous changes in marriage and divorce patterns, through both strengthened and weakened control over abortion, birth seasonality patterns in most parts of the world have remained constant," wrote Gabriele Doblhammer and Joseph Lee Rodgers, the authors of a study of seasonal birth trends in Austria in the 19th and 20th centuries.

The September peak, common to both the US and the European pattern, is generally attributed to conceptions occurring during the Christmas break. Given time to spend at leisure, and not much else to do, peoples' thoughts will naturally turn to private amusements. Two American economists, David Lam and Jeffrey Miron, found September peaks in births in every Christian country they studied, from both the northern and the southern hemisphere. This result argues strongly that Christmas has an effect, but that temperatures at Christmas do not.

Other bits of evidence also point to a rise in sexual activity over Christmas. Sales of condoms peak before Christmas, and slump the week after, Kaye Wellings and colleagues from the London School of Hygiene and Tropical Medicine reported in 1999. Sexually transmitted infections peak in the first quarter of the year, and so do terminations.

So if the Christmas effect is real, what about the possibility that a cold Christmas will enhance it? Lam and Miron suggest not, but they don't rule out temperature effects. Baking summers in the southern US are, they suggest, responsible for the spring trough in US births. My, it's just too hot...

As a simple check I compared average December temperatures for central England (a record exists from the 17th century) with births in England and Wales the following September.

Taking eight cold Decembers since 1960, and eight warm ones, I could find no link between temperature and the September peak. The exceptionally cold Decembers of the early Sixties were followed by no September peak at all, yet births did peak in that month after the warm Decembers we experienced in 1985, 1994 and 2002.

This is far from conclusive. A comparison with Christmas temperatures, rather than averages for December, might produce a different result. The figures I compared do hint at a more consistent September peak in recent years than in earlier ones, for which the obvious explanation would be the increasing length of the Christmas holiday. But that's a guess.

This month's deliveries will tell us if there really has been a surge in births, beyond the usual September peak, and if it extends beyond Portsmouth. It would be extraordinary if there were.

Nigel Hawkes (born in September 1943) is director of Straight Statistics (straightstatistics.org)

React Now

  • Get to the point
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
iJobs Job Widget
iJobs General

Recruitment Genius: Service Advisor

£16000 - £17000 per annum: Recruitment Genius: Due to expansion and growth of ...

Recruitment Genius: Service Advisor

£16000 - £17000 per annum: Recruitment Genius: Due to expansion and growth of ...

Recruitment Genius: SEO Account Manager

£26000 - £35000 per annum: Recruitment Genius: An SEO Account Manager is requi...

Recruitment Genius: Telesales / Telemarketing Executive - OTE £30k / £35k plus

£18000 - £35000 per annum: Recruitment Genius: This company specialises provid...

Day In a Page

Read Next
 

Hollywood: Stop trying to make Superman cool. The world needs a boy scout in blue

Matthew Daly
A man enjoys the  

If you really want to legalise cannabis, then why on earth would you go and get high in a park?

Peter Reynolds
Revealed: Why Mohammed Emwazi chose the 'safe option' of fighting for Isis, rather than following his friends to al-Shabaab in Somalia

Why Mohammed Emwazi chose Isis

His friends were betrayed and killed by al-Shabaab
'The solution can never be to impassively watch on while desperate people drown'
An open letter to David Cameron: Building fortress Europe has had deadly results

Open letter to David Cameron

Building the walls of fortress Europe has had deadly results
Tory candidates' tweets not as 'spontaneous' as they seem - you don't say!

You don't say!

Tory candidates' election tweets not as 'spontaneous' as they appear
Mubi: Netflix for people who want to stop just watching trash

So what is Mubi?

Netflix for people who want to stop just watching trash all the time
The impossible job: how to follow Kevin Spacey?

The hardest job in theatre?

How to follow Kevin Spacey
Armenian genocide: To continue to deny the truth of this mass human cruelty is close to a criminal lie

Armenian genocide and the 'good Turks'

To continue to deny the truth of this mass human cruelty is close to a criminal lie
Lou Reed: The truth about the singer's upbringing beyond the biographers' and memoirists' myths

'Lou needed care, but what he got was ECT'

The truth about the singer's upbringing beyond
Migrant boat disaster: This human tragedy has been brewing for four years and EU states can't say they were not warned

This human tragedy has been brewing for years

EU states can't say they were not warned
Women's sportswear: From tackling a marathon to a jog in the park, the right kit can help

Women's sportswear

From tackling a marathon to a jog in the park, the right kit can help
Hillary Clinton's outfits will be as important as her policies in her presidential bid

Clinton's clothes

Like it or not, her outfits will be as important as her policies
NHS struggling to monitor the safety and efficacy of its services outsourced to private providers

Who's monitoring the outsourced NHS services?

A report finds that private firms are not being properly assessed for their quality of care
Zac Goldsmith: 'I'll trigger a by-election over Heathrow'

Zac Goldsmith: 'I'll trigger a by-election over Heathrow'

The Tory MP said he did not want to stand again unless his party's manifesto ruled out a third runway. But he's doing so. Watch this space
How do Greek voters feel about Syriza's backtracking on its anti-austerity pledge?

How do Greeks feel about Syriza?

Five voters from different backgrounds tell us what they expect from Syriza's charismatic leader Alexis Tsipras
From Iraq to Libya and Syria: The wars that come back to haunt us

The wars that come back to haunt us

David Cameron should not escape blame for his role in conflicts that are still raging, argues Patrick Cockburn
Sam Baker and Lauren Laverne: Too busy to surf? Head to The Pool

Too busy to surf? Head to The Pool

A new website is trying to declutter the internet to help busy women. Holly Williams meets the founders