It has long been thought you can't definitively tell if your baby will be left or right-handed until they're in their toddler years.
But a new study suggests you may be able to figure it out before a child is even born - based on which thumb they suck in the womb.
It was once thought that hand preference comes from the brain, but eLife journal suggests it may form due to gene development when the spine is forming.
Researchers from the Netherlands and South Africa analysed spinal cord genes of fetuses between eight and 12 weeks of pregnancy. A correlation was found between detected left and right differences, and the thumb that the baby preferred to suck in the womb.
The scientists found that babies picked one dominant thumb before the connection is made between their spinal cord and the motor cortex in the brain.
The eLife journal is a non-profit, peer reviewed journal led by biomedical scientists.
The study is still in process and there is still further research to conduct. However, it may be one small detail that carries more significance than once thought.