The 'Christmas Effect': Why more people get pregnant during the holidays than any other time

Silhouette of couple kissing under mistletoe with pink background.
Why more people get pregnant during the holidays than any other time. (Photo: Getty Images)

The holiday season is the time for admiring festive lights, opening presents, gathering with friends and family — and, apparently, making a baby.

According to a 2020 study published in the journal Human Reproduction, researchers from Boston University explored why late fall and early winter may be linked to a higher likelihood of conception, based on the data that birthdays in the U.S. peak during the month of September. They noticed a decline in fecundability — a term that refers to the probability of getting pregnant within one menstrual cycle — in the late spring and an increase in the late fall.

The researchers also found that those living in the southern states showed a 45 percent surge in quick conceptions during the latter part of November.

“In Florida, we have noticed higher birth rates in July and August, and there is something very interesting known as the ‘Christmas Effect,’” Dr. Christine Carlan Greves, an ob-gyn at Orlando Health Winnie Palmer Hospital, tells Yahoo Life.

She points to a review published in the Journal of Obstetric, Gynecologic & Neonatal Nursing that analyzed international research conducted between 1938 and 2001 to determine why the number of births peaked during September in the U.S., Canada, Mexico and Europe. The author theorized that biometeorology (the science of atmospheric processes, including seasons and weather, and living organisms, like people) and psychosocial (a combination of psychological and social) factors appear to play roles in this conception trend.

“In cooler climates, where folks are less apt to venture out in the winter, they may have more time to be home making babies,” Kate Balestrieri, psychologist, sex therapist and founder of the group therapy practice Modern Intimacy, tells Yahoo Life. The drop in temperature may also encourage couples to snuggle up more often. “Cool weather can incite a desire for closeness and nostalgia or a desire to be in connection,” she says.

Balestrieri adds that being surrounded by relatives during the last six weeks of the year could bring on thoughts of contributing to one’s family tree. “Some people may feel a pull or familial pressure to create their own family,” she says.

Other couples may be dealing with feelings of melancholy during this time of year. “The holidays can bring up feelings of loneliness, which can compel some folks to prioritize having children,” adds Balestrieri.

There may also be an evolutionary reason why many conceptions take place between Turkey Day and New Year’s Day. “Evolutionary theorists posit that mammals with longer gestational periods tend to unconsciously prioritize pregnancy during the shorter days and cooler months, rendering a birth date when the weather is warmer and resources more available,” Balestrieri says. “This may translate into conscious preferences to be pregnant when it’s easier to bundle, and for pregnancy to be complete by the summer months.”

But, as Greves points out, it could simply be the fact that many people take some vacation days toward the end of year and may be less stressed. “Could it be because people are more relaxed during their time off from work during the holidays?” she says. “There are many theories, but we don’t have any good causation studies as to why this is a phenomenon.”

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