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Is oldest daughter syndrome backed by science? New study suggests it is

New research looks into oldest daughter syndrome
New research looks into oldest daughter syndrome 01:50

What was once coined as a phrase to describe the protective and responsible tendencies of older sisters is getting some backing from new research.

In a first-of-its-kind study, UC Merced Professor Jennifer Hahn-Holbrook hopes it sheds light on the need to understand more about the stress pregnancy can have on children.

"This was the first study of its kind. It's a really unique study because we were able to follow about 250 families from pregnancy all the way until the kids were about 15 years old," Hahn-Holbrook said. "There really hasn't been a lot of research like this, the long-term effects of stress and pregnancy."

The research found that mothers tended to depend on firstborn daughters to help in caring for younger siblings, especially in high-stress environments.

"We hypothesize that this was to provide mothers with a helper at the nest. So, when you're in a stressful environment, right, it's going to be harder to raise those children and keep them alive," Hahn-Holbrook said.

"So it might have been in Mom's best interest, but unconsciously, she's speeding the development of her firstborn girls so that she has a helper at the nest."

The research was done in partnership with UCLA researchers and found the impact on early brain development was only recorded in firstborn daughters, with little to no effect on the brain development of firstborn boys.

"So, in firstborn boys, no matter how stressed the mom was, we didn't find an increase in puberty timing, and so it was girls who were whose mothers were stressed and who were the ones who were developing earlier," Hahn-Holbrook said.

Hahn-Holbrook said it's important to note that the only development was in adrenal puberty which impacts the brain development, not gonadal puberty.

"It doesn't speed up reproduction, it does speed up socio-emotional development. So the hormones for adrenal puberty are really helping to mature the brain," Hahn-Holbrook said.

Hahn-Holbrook said as a first-born daughter herself, it really helps to understand the biological development that may have shaped her own way of relating to her family. She hopes this is just the first of many studies into how stress during pregnancy can impact children.

"The biggest takeaway is that stress and pregnancy really matters and can really affect the trajectory of firstborn girls," Hahn-Holbrook said.

You can read more about the study here.

The official research findings can be found here.

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