“We typically have more babies born in July, August and September,” says Mary Lou Kopas, chief of midwifery at University of Washington Medical Center - Northwest. “Count back nine months and, well, we’re looking at November to January.”
The evidence isn’t purely anecdotal, either. According to the National Center for Health Statistics, more babies are born in northern states like Washington around June and July, while southern states experience a peak a bit later in October and November. That means prime conception time in the United States occurs in fall and winter.
Is it the cozy sweater weather that’s causing us to turn up the heat? Do our longer nights have something to do with it? Or is it something biological that we just can’t explain?
Kopas shares her thoughts on the matter as well as some helpful facts for what to know if you hope to get pregnant this winter.
Why more babies are conceived in fall and winter
Close your eyes for a moment and picture Bambi. In your imagination that little white-tailed fawn is probably frolicking in a grassy meadow studded with wildflowers — and there’s a reason for that.
In the animal kingdom, many newborns emerge right around springtime, when food sources are plentiful again and the likelihood of survival is much higher. To get this timing right, certain species have evolved to the point where females only go into estrus (aka heat) during specific seasons.
The same could be true of humans, Kopas says, but there’s not enough solid evidence to say one way or another.
Social aspects like spending more time in bed when it’s cold and dark may play a part, she speculates, while biological factors similar to what goes on in the animal world could also factor into conception trends.
“Obviously, humans menstruate once a month, and we know that people conceive all times of the year, but there could be a biological factor that makes us more fertile at certain times,” she explains. “The thing about humans, though, is that while we’re mammals, we have evolved to the point where we can control our environment, and sociological factors are much bigger for us.”