Rapidly scaling startups often make rushed hiring choices that disadvantage women, a recent study has found.

The findings draw on more than 31,000 new ventures founded in Sweden between 2004 and 2018.

Researchers at the Stockholm School of Economics report that in male-led startups, scaling reduces the odds of hiring a woman by about 18 per cent, and the odds of appointing a woman to a managerial post by 22 per cent.

Mohamed Genedy is co-author and postdoctoral fellow at the House of Innovation, Stockholm School of Economics.

Genedy  said: “During those moments of rapid growth, even well-intentioned leaders can fall back on familiar stereotypes when assessing who they believe is best suited for the role.”

The patterns emerge even in Sweden, regarded as a highly gender-equal national context.

Founders with human resources-related education counteract these challenges.

In ventures led by founders with HR training, the odds of hiring a woman increase by more than 30 per cent, and the odds of appointing a woman to a managerial role increase by 14 per cent for the same level of growth.

Genedy said: “When founders have experience with structured hiring practices, the gender gaps shrink, and in some cases even reverse.

“This shows that getting the basics of HR right early on really pays off.

“When things start moving fast, founders with HR knowledge are less likely to rely on biased instincts and more likely to hire from a broader talent pool.”

Prior experience in companies with established HR practices also helps, though to a lesser degree.

It raises the likelihood of hiring women as ventures scale, but does not significantly affect managerial appointments.

The study additionally shows these patterns are not driven by founder gender alone.

Even solo female-led ventures display similar tendencies when growing rapidly, though to a somewhat lesser degree.

In female-dominated industries, rapid growth increases the hiring of women for regular roles but still reduces the likelihood that women are appointed to managerial positions.

“When scaling accelerates, cognitive bias kicks in for everyone. Female founders are not immune to these patterns,” said Genedy.

High brain oestrogen may raise women’s PTSD risk if severe stress strikes during high oestrogen phases, causing memory problems and stronger fear responses, new research has revealed.

The study found that exposure to several simultaneous stressors can lead to persistent memory problems, difficulty recalling events and stronger reactions to trauma reminders.

Tallie Baram is distinguished professor of paediatrics, anatomy and neurobiology, and neurology at UC Irvine’s School of Medicine, and led the research.

Baram said: “High oestrogen is essential for learning, memory and overall brain health.

“But when severe stress hits, the same mechanisms that normally help the brain adapt can backfire, locking in long-lasting memory problems.”

Oestrogen, which usually supports learning and memory, can increase vulnerability when levels are high in the hippocampus, a brain region central to memory formation and retrieval.

Researchers reported that female mice stressed during cycle phases with high oestrogen developed enduring memory loss and heightened fear of reminders, while lower levels were protective. Males, who also have high hippocampal oestrogen, were susceptible more mildly and through different receptor pathways.

High oestrogen loosens the packaging of DNA in brain cells, known as permissive chromatin.

This normally helps learning, but under extreme stress it can allow harmful, lasting changes in memory circuits.

Memory problems were driven by different oestrogen receptors in men and women, alpha in men and beta in women.

Blocking the relevant receptor prevented stress-related memory issues even when oestrogen stayed high. Vulnerability depended on hormone levels at the time of stress, not afterwards.

Co-author Elizabeth Heller is associate professor of pharmacology at the University of Pennsylvania Perelman School of Medicine.

She said: “A lot of what determines vulnerability is the state your brain is already in.

“If a traumatic event hits during a period when oestrogen is already unusually high, the biology can amplify the impact in lasting ways.

“This study shows that a state of high oestrogen in a specific brain region promotes vulnerability to stress in both male and female subjects.”