Daily newspaper Le Parisien reports that twice as many children are born in France on September 23rd than on other days.

Using some simple mathematics to count backwards the average 265 days of a pregnancy leads to January 1st.

“There is a New Year’s Eve effect,” said Arnaud Régnier-Lollier, a researcher at the national institute of demographic studies (INED), who identified the sudden jump in births.

“Couples tend to be together on that evening and more likely to let their hair down,” he told the newspaper. “But there’s also, without doubt, an increase in unplanned pregnancies as a result of people paying less attention to contraception due to partying.”

The accompanying statistics showing an increase in abortions during January and February could support this theory.

The increase in births in September marks a change from the traditional high point seen in May during the 1970s and 1980s. Indeed, a quarter of women still think of May as the best time to give birth, while only 2 percent prefer September, says Arnaud Régnier-Lollier.

He believes another factor is at work. As couples wait longer to have children, they may not conceive as quickly, even if they hope to have a child earlier in the year.

“It’s possible that couples, who are starting to have babies much later in life, stop using contraception in August, but don’t manage to conceive until four months later,” he said.

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