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New study suggests winter babies face socioeconomic disadvantages

January 08, 2009

Many of us may often feel that we've been born under an unlucky sign. Now, new research by a pair of University of Notre Dame economists suggests that some of us are, in fact, born in an unlucky season.

In their paper, Kasey Buckles and Daniel Hungerman point out that a large body of previous research consistently has found that people born in December, January and February are, on average, less educated, less intelligent, less healthy and lower paid than people born in other seasons.

A variety of explanations have been suggested for this phenomenon, including such social and natural factors as compulsory schooling laws, changes in climate and exposure to illness. However, the exact cause of the association between season of birth and later outcomes has never been precisely clear.

In the new study, Buckles and Hungerman analyzed U.S census data and birth certificates to determine if the typical woman giving birth in winter is any different from the typical woman giving birth at other times of the year.

They discovered that babies born in the winter are more likely to have mothers who are unmarried, who are teenagers or who lack a high school diploma. One explanation for the seasonal patterns in births is that summer's high temperatures inhibit sperm production. This seems to affect lower socioeconomic status women more adversely, which could explain why there are relatively fewer births to these women in the spring and early summer.

Buckles and Hungerman also point out that there could be a "prom babies" effect, with winter births occurring nine moths after end-of-year school celebrations.

The researchers also note that survey data has shown that women consider winter the least desirable season in which to give birth. Buckles and Hungerman suggest that women who are wealthier and more educated are better able to time their births to more desirable seasons.

University of Notre Dame