It's Science: Moms & Their Kids Are More Likely To Share A Birth Month

My daughter was due on my birthday — and appeared in this world just a few days before I turned 34. And my older daughter was born just a few weeks earlier in the year than the two of us. By the time we get to my birthday each year, everyone in the family is absolutely sick of cake. And that’s crazy for a house with so many pisces.

Now, what I thought was also a kind of cute family birthday coincidence has turned out to be an actual “phenomenon” discovered through science. It’s actually more likely that your kid shares your birth month and it’s also more likely for siblings to share a birth month and for partners to share a birth month — all according to a new study.

The study, which appeared in the latest issue of the journal Population Studies, examined the births of babies in Spain and France during 12 years between 1980 and 2019 — about 10 million births. The surprising finding was that you are more likely to share a birth month with an immediate relative than you are with someone off the street — and we are not sure why.

Specifically, there were 4.6% more births where mothers and their kids shared the same birth month than would be statistically expected. Siblings were 12.1% more likely to share a birth month than expected and dads and their kids were 2 percent more likely.

While researchers can’t say what causes this fun statistic, they are guessing that it might be a combination of biological and social factors.

"What could cause the higher probabilities of family members being born in the same season? The potential explanations seem to be both social and biological," Dr. Adela Recio Alcaide, an epidemiologist at the University of Alcala, told Science Daily.

She also points out that romantic partners are also more likely to share a birth month, which points to at least some amount of social influence, since people more often date within their demographics.

Why is this information important? The study’s authors note in the study that it could impact any other study done regarding the effect of a child’s birth month on other factors, such as personality, behavior, or test scores.

Previous studies have found that moms and their kids more often share a birth season, but this is the first study to find that the month itself is also more common. But really — who is going to do the work of finding out if moms and babies more often share an astrological sign? We’re waiting.