Do you and your mom share the same birth month? Scientists reveal the phenomena is common – and they know why

It is a strange phenomenon, as mothers and children share the same birth month.

While this sounds like a one-in-a-million event, a new study finds that it occurs more commonly than expected.

Researchers from Spain and the United States analyzed 10 million births from 1980 to 1983, from 2016 to 2019, from 2000 to 2003, and from 2010 to 2013, and found that there was a 4.6 percent increase in births in which the mother and child shared the same month of birth. Than was expected.

The team believes the results are due to socio-demographic characteristics, as people from similar backgrounds are known to intermarry and be more likely to give birth at certain times of the year.

Dr. Adela Recio Alcaide, an epidemiologist at the University of Alcala, said: What could cause an increase in the odds of family members giving birth in the same season?

“Possible explanations appear to be social and biological.”

The team looked at the mothers' socio-demographic characteristics, such as maternal education, age, parity, repartnering, race, social class, birth order, or legality.

The team looked at all births in Spain from 1980 to 1983 and 2016 to 2019 and all births in France from 2000 to 2003 and 2010 to 2013.

The records provided the child's month of birth, as well as data on his parents and the sibling closest to him in age.

The researchers shared that birth in a given country tends to follow a pattern, with more babies being born at certain times of the year than at others – this is known in the academic literature as birth seasonality.

However, the team wanted to know if the mothers and babies shared the same birth month.

The data showed an increase In January births among mothers born in January, the same thing was observed among February children, and so on.

The team believes the results are due to socio-demographic characteristics, as people from similar backgrounds are known to intermarry and be more likely to give birth at certain times of the year.

This was true for both countries and for all four time periods studied.

The team also found similar cases between siblings, where the number of siblings born in the same month was 12.1% higher than assumed.

The study also found a 4.4% increase in births with parents with the same birth month and 2% more with both children and father.

“In Spain, for example, a woman with a higher education is more likely to give birth in the spring than a woman without a higher education,” the researchers noted.

“If she has a daughter, in addition to the possibility of her being born in the spring, that daughter is more likely to get a higher education because her mother did.

“So, when this daughter has babies, she will most likely have them in the spring as well.”

These results are likely due to the daughter being allowed to obtain the same higher education as her mother.

Factors that can influence the biology of fertility, such as food availability and sunlight exposure, can also vary according to a person's background.

It seems that the increase in the number of children born to fathers and mothers in the same month is due to social or behavioral reasons before pregnancy related to choosing a partner born in the same month, as we observed this surplus in marriage statistics. Couples are more likely to mate with someone of the same month, Recio-Alcaide said.

“This may not be surprising given that things like partnerships tend to be formed by people with similar socio-demographic characteristics,” adds co-author Professor Luisa Burrell, from the City University of New York.

“Furthermore, biological factors known to influence birth seasonality—such as exposure to photoperiod, temperature, humidity, and food availability—also depend on sociodemographic characteristics since different social groups are exposed to these biological factors to varying degrees.” He added.