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

Scientists believe they have figured out why so many mothers were born in the same month as their babies.

Researchers from Spain and the United States analyzed 10 million births from 1980 to 2013 and found that the phenomenon is more common than previously thought.

In fact, there were 4.6 percent more births in which mom and baby were born in the same month than previous estimates would suggest.

There were also 12.1 percent more cases than expected of siblings having birthdays in the same month.

The team believes the results depend on sociodemographic characteristics: People of similar backgrounds are known to pair up and be more likely to give birth at certain times of the year.

Researchers from Spain and the United States analyzed 10 million births between 1980 and 1983, 2016 and 2019, 2000 and 2003 and 2010 and 2013, finding that births in which mother and child were born on the same same month, it was 4.6 percent more than expected.

Dr Adela Recio Alcaide, an epidemiologist at the University of Alcalá, said: “What could be the reason for the higher probability of family members being born at the same time of year?”

“Potential explanations appear to be both social and biological.”

The team looked at mothers’ sociodemographic characteristics, such as mother’s education, age, parity, repartnership, race, social class, birth order, or legality.

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

The records show the month of birth of the child, as well as the month of birth of his parents and the sibling closest to them in age.

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

However, the team wanted to see if the birth months of the mother and baby were the same.

Data showed a spike January births in mothers born in January, the same was observed in February babies, etc.

The team believes the results depend on sociodemographic characteristics: People of similar backgrounds are known to pair up and be more likely to give birth at certain times of the year.

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

The team also found similar patterns among siblings, with 12.1 percent more siblings born in the same month than expected.

The study also found 4.4 percent more births for parents born in the same month, and two percent more for children and the father.

“In Spain, for example, a woman with a university degree is more likely to give birth in the spring than a woman without a university degree,” the researchers note.

“If she has a daughter, in addition to being more likely to be born in the spring, that daughter has a better chance of getting a college education because her mother has one.

“So when this daughter has children, they will most likely have them in the spring too.”

These results were likely due to the fact that the daughter received the same college education as her mother.

Factors that can influence fertility biology, such as food availability and exposure to sunlight, can also vary depending on a person’s background.

“The excess number of children whose father and mother were born in the same month appears to be due to preconception social or behavioral reasons that relate to the choice of a partner born in the same month, as we observed this excess in marriage statistics. , with spouses more likely to marry someone from the same month,” said Recio Alcaide.

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

“Furthermore, biological factors that are known to influence the seasonality of fertility, such as photoperiod, temperature, humidity and food availability, are also influenced by sociodemographic characteristics, as different social groups are affected to varying degrees by these biological factors,” — Borrell. added.