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Super Bowl Babies: More Boy Births 9 Months Later?

Super Bowl Babies: More Boy Births 9 Months Later?

Ah, Super Bowl Sunday. One of the unofficial national holidays of Americans, and second only to Thanksgiving in the amount of food and drink consumed. The annual championship game of the National Football League in the U.S. is often the most-watched television event of the year.

After any big event — whether man-made or natural — researchers often find surprising trends in birth rates. When you follow the data, all sorts of interesting things can be discovered.

Let’s find out how Super Bowl Sunday influences birth rates in America.

Face it, the Super Bowl has become one of those annual pastimes that Americans often use as an excuse to gather, socialize, party, and for some, watch a sometimes-exciting, but all-too-often boring game of American football. Great teams who had an off year watch forlornly from their own homes, hoping for another shot at the title game next year.

For many couples, a part of the party-like atmosphere that surrounds Super Bowl Sunday involves sex. For psychological reasons, humans seem to have more sex than usual around a major event, whether it’s man-made like this one, or natural (think after a natural disaster, and everyone is safe).

Grech & Zammit (2018) were interested in the question of how the male-to-female ratio of births is impacted by Super Bowl Sunday, and whether any significant changes they found were influenced by race or area of the country.

According to the researchers, births by race and region were obtained from the Centers for Disease Control and Prevention (the CDC Wonder online database). Since the Super Bowl occurs at the beginning of February every year, in order to determine any effect on birth rates, monthly time series for the period 2003 (for the year 2002) through to 2015 for males, females, and ratio of the two genders were analyzed. “Data was grouped into four US census regions with the four different races for each region,” they noted.

The researchers ended up analyzing more than 53 million births during this time period and found just over 27 million males and nearly 26 million females were born. As you can see, there’s a slight edge in male births to begin with, so the researchers needed to adjust their analyses to account for seasonality and other factors that may otherwise cause a significant finding to be hidden in the data.

Stress Causes Fewer Males to Be Born, Positive Events Cause More Males to Be Born

The present study found support for the hypothesis that male births tended to increase nine months after the Super Bowl was played. The effect, however, is very small and appears to be really only significant from a statistical point of view. The way the researchers couched their findings suggest as much too:

It is possible that increased coital rates during this period (perhaps due to a combination of celebration and inebriation) may result in the M/T rises nine months later observed in this study.

It’s possible? They may result? They don’t sound too sure of themselves there.

As the researchers note, previous studies have found that stress causes dips in the male-to-female ratio of births, resulting in fewer males being born after stressful events. The Trivers-Willard hypothesis explains this dip as being caused by stressed women who “spontaneously terminate weaker fetuses when experiencing poor conditions. These losses are usually male since males require more maternal resources in order to reach term.”

After World Wars I and II, a study showed an increase in the male birth rate in the countries that were on the winning side of the wars (Macmahon & Pugh, 1953; Russell, 1936). Other research has confirmed this finding. After the birth of Prince William in 1982, male births in England and Wales were up nine months later (Grech, 2015). After South Africa won the 2010 FIFA World Cup, male births rose nine months later in that country too (Masukume & Grech, 2015).

There seems to be something to the idea that during stressful times, fewer males are born, while during times of elation and celebration, more males are born.

Think about that when reflecting on this Super Bowl Sunday, whether you were rooting for the Eagles or the Patriots. Nine months from now, don’t be surprised if there are more baby boys than girls being born in the country.


Grech, V. & Zammit, D. (2018). Influence of the Super Bowl on the United States birth sex ratio. Early Human Development, In press, corrected proof, Available online 19 January 2018

Grech, V. (2015). Historic Royal events and the male to female ratio at birth in the United Kingdom, Eur. J. Obstet. Gynecol. Reprod. Biol. 191, 57–61.

Macmahon, B. & Pugh, T.F. (1953). Influence of birth order and maternal age on the human sex ratio at birth, Br. J. Prev. Soc. Med. 7, 83–86.

Masukume, G. & Grech, V. (2015). The sex ratio at birth in South Africa increased 9 months after the 2010 FIFA world cup, Early Hum. Dev. 91, 807–809.

Russell, W.T. (1936). Statistical study of the sex ratio at birth, J. Hyg. 36, 381–401.

Our sincerest thanks to Science Direct for access to this academic article, which is in press.

Super Bowl Babies: More Boy Births 9 Months Later?

John M. Grohol, Psy.D.

Dr. John Grohol is the founder of Psych Central. He is a psychologist, author, researcher, and expert in mental health online, and has been writing about online behavior, mental health and psychology issues since 1995. Dr. Grohol has a Master's degree and doctorate in clinical psychology from Nova Southeastern University. Dr. Grohol sits on the editorial board of the journal Computers in Human Behavior and is a founding board member of the Society for Participatory Medicine. You can learn more about Dr. John Grohol here.

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APA Reference
Grohol, J. (2018). Super Bowl Babies: More Boy Births 9 Months Later?. Psych Central. Retrieved on October 27, 2020, from
Scientifically Reviewed
Last updated: 8 Jul 2018 (Originally: 4 Feb 2018)
Last reviewed: By a member of our scientific advisory board on 8 Jul 2018
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