If you had sisters growing up, you know about that weird hormonal thing that sometimes caused your periods to be in sync. You also may remember getting it around the same time as the girlfriends you spent every day with—because you played softball together or were on the same cheerleading squad, or hung out every day after school. Whatever it was, being physically near other girls often meant you all made a tampon and Midol run at the same time of month.
Well, now that we are boring old adults and those fickle teen years are in the past, there’s one thing that hasn’t really changed. Women still have the power to influence other women’s reproductive cycle. Only this time it’s not the fear of getting our periods before going to the beach with our crush from homeroom. Now, it’s making a baby that can be contagious.
According to an article published in Demographic Research, there’s a reason women tend to send out baby announcements around the same time as their girlfriends. A study that spanned over a decade revealed the likelihood that pregnancy was “contagious” among women who spend a lot of time together. Much like our teen years when my sister and I were PMSing simultaneously and causing a super memorable and joyful time for our parents, grown women turn into baby factories in much the same way.
The study began in the mid-1990s when the participants were still adolescents. The researchers then followed them for the next 10-15 years, charting all their pregnancies, and found that yes, in fact, if a woman’s friends are having babies, she’s more likely to have babies in that same time frame.
Interestingly though, this “likelihood” or “contagion” is what the researchers call “short-term and inverse U-shaped.” This means that an individual’s risk of childbearing increases after a friend’s childbearing, reaches a peak around two years later, then decreases. So basically your friend spits out a kid, you hold them, soak in the new baby smell, and — BAM! — you want a baby.
Not surprisingly, when that tiny, sleepy, adorable newborn morphs into a baby rhinoceros who pillages everything in their wake, your desire to have one of your own decreases. Apparently, once you see a 2-year-old destroy their mother’s couch with a sharpie and smear poop on the bathroom wall, you’ve switched from OMG MY OVARIES I WANT ONE to meh, I think I’m good.
Other factors that make us have babies when our friends do are: age, finances, and fear of being left behind. Women who are concerned with the ticking of their biological clock may see the growing bellies of their similarly-aged friends and then worry about their own child-bearing window. And, it’s no secret that we, as women, want to feel included—just like when we were kids.
When we have babies around the same time our friends do, we can still participate in the conversation. We can all simultaneously make the switch from happy hour to play dates. We can talk about nannies and daycares and the cost of diapers and formula coupons. If you’re still blowing $200 on hot new new boots and going out to dinner three nights a week, all of a sudden you have nothing in common with your exhausted, unshowered girlfriends who are newly-minted moms.
The other interesting thing this study found is that pregnancies are only contagious among friends—not siblings—and only lead to planned pregnancies. The study found no noticeable connection between family members influencing pregnancies, nor does holding your friend’s wrinkly new baby cause you to spontaneously procreate if you aren’t ready to do so.
When I look back at my five-year-span of baby making, it all makes sense. I was 28 when I had my first child, and more than ready. Immediately upon entering the SAHM world, I joined playgroups where I surrounded myself with other mothers in the same place—physically, emotionally, and financially. We were all in the season of pregnancies, breast or bottle feeding, never sleeping through the night, and changing diaper upon diaper upon diaper.
Soon after one, most of us popped out another. And so on. Someone was always announcing a pregnancy or nearing the end of a pregnancy or somewhere in between. We always had a meal train going for the latest mom to give birth, and we endlessly swapped hand-me-downs and war stories of blow-out diapers and toddler tantrums in Target.
Was it “contagious” or just mere chance that most of my friends were having babies when I had babies? Was it my choice to surround myself with women in the same place in life? Or did I have a greater desire to make more humans as each of my friends did?
I guess I’ll never really know for sure, as that season in my life has passed. Maybe pheromones caused my period cycle synced with my teenage friends and sister. And maybe my adult girlfriends’ life choices influenced when I had my babies.
Regardless, I treasure those years close to my heart. Those women were my lifeline at a time when I had never needed a lifeline more. They were my confidants, my support, my shoulder to cry on, my go-to babysitters in an emergency. They were my “sisters” in motherhood.
So whether or not they influenced my desire or even ability to link up a good swimmer with a good egg, I’m forever grateful that they were by my side when I did.