Kasey Buckles and Daniel Hungerman of the University of Notre Dame point out that a large body of previous research consistently has found that people born in December, January and February face socioeconomic disadvantages.

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 the rest of the year.

The study, published as a National Bureau of Economic Research working paper, found babies born in the winter are more likely to have mothers who are unmarried, who are teenagers, or who lack a high school diploma.

The researchers said possible explanations include summer's high temperatures may inhibit sperm production or winter births occur nine moths after the end of prom season.

The researchers also noted women say winter is the least desirable season in which to give birth and the researchers suggest wealthier and more educated women are better able to time their pregnancies.