Autistic features in girls from a psychiatric sample are strongly associated with a low 2D:4D ratio.

Researchers measured the index-to-ring-finger length ratio (2D:4D) in girls from a psychiatric unit. They also rated each girl's autistic traits with standard checklists. The team wanted to see if a lower, more 'masculine' digit ratio tracked with more autistic features.

The same measures were taken for boys, but the main focus was on the girls.

Girls with lower 2D:4D scores showed markedly more autistic traits. The link was strong and negative, meaning the shorter the ratio, the higher the trait count. The pattern appeared in boys too, but the numbers were weaker.

Hönekopp (2012) pooled many studies and agrees: people with autism usually have lower 2D:4D than controls. That meta-analysis now wraps this 2009 girl-focused result into the bigger picture.

Spackman et al. (2023) and Sutton et al. (2022) extend the sex-difference theme. They show current tools miss girls because their repetitive behaviors look different—more sensory, less obvious. The finger-ratio clue could help catch those easily-overlooked girls earlier.

Herrnstein et al. (1979) seems to clash at first glance. That older paper found finger-print ridge patterns were too messy to help diagnose autism. The difference is method: ridge counts versus ratio lengths. Ratios stayed useful; ridge detail did not.

You can add a thirty-second finger-length check to your intake. A markedly low 2D:4D in a girl gives you one more data point that nudges toward deeper autism screening, especially when camouflaging or subtle sensory behaviors cloud the picture. It is cheap, quick, and now backed by a meta-review.