You ever noticed you’re buying more birthday presents in the summer than the winter? The Daily Beast reports its no coincidence — the winter is the time for conception, so more babies are born in the late summer and early fall.

A study published in the journal Obstetrics & Gynecology about 10 years ago delved into the question of seasonal conception, finding that time and weather heavily affect when couples are able to conceive a child.

They’ve concluded that couples conceived most in the month of December, as 9 percent of babies were made in that month, and in contrast, August is the month where the least amount of babies were made, according to one of the study’s author.

Their reasons for this occurrence is the male having diminished semen during the hotter climates.

“Biological hypotheses include deterioration of sperm quality during summer, seasonal differences in anterior pituitary-ovarian function caused by changes in the daylight length, and variation in quality of the ovum or endometrial receptivity. Increased sexual activity associated with end-of-the-year holiday festivities has also been postulated,” said the author of the study.

The study shows that sex and the pursuit of it increases during the Christmas season, and the emotional joys associated with the holidays increases couples desire for sexual activity. “The period from Christmas to New Year is associated with increased opportunities for socializing and generally more hedonistic approach to life,” said the author.

Results from a different study published in the Journal of Circadian revealed that time of day also impacts the frequency of intercourse, showing that most couples tend to have sex when its bedtime from the times 11p.m through 1a.m. The main reason for this according to sex expert Carol Queen is that night is typically the most convenient time slot for couples to have intercourse.

“People have sex subject to availability, and when they are partnered, bedtime not only provides that availability, but it possesses a certain amount of cultural coding,” she said.

Queen also gathers that the day of the week also affects you and your partners willingness for sex. Results from studies show that Sunday is the least popular day for intercourse, and Friday and Saturday are more popular for sex by 18 percent.

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