‘Eldest daughter syndrome’ is a popular concept on social media, and centres around the added responsibilities and emotional weight often shouldered by eldest daughters.

The study suggests there may be some truth behind the cultural phenomenon, with researchers finding first-born daughters tend to mature earlier, allowing them to assist in caretaking for younger siblings.

The research team found a correlation between early signs of adrenal puberty in first-born daughters and their mothers having experienced high levels of prenatal stress.

Jennifer Hahn-Holbrook, co-authors of the study and an assistant professor of psychology at the University of California, said a daughter maturing early is beneficial for the mother. 

“It gives Mom a ‘helper at the nest’ sooner, aiding the women in keeping the latter offspring alive in difficult environments,” she said.

The study also monitored results of pregnant women during the first-trimester prenatal care visits.

For half of the mothers, it was their first pregnancy and they were non-smoking in addition to not using steroid medications, tobacco, alcohol or other recreational drugs.

Researchers measured the mother’s depression and anxiety levels throughout their pregnancy and certain features of adrenal puberty in the children after birth, finding that eldest daughters matured the fastest when their mothers had high levels of prenatal stress.

The same was not found for eldest sons or daughters who were not first-born.

“One reason that we didn’t find this effect in first-born children who are sons could be that male children help less often with direct childcare than female children do, so mothers have less of an adaptive incentive to speed their social pubertal development,” Hahn-Holbrook said.