When Does One Become Right Handed or Left Handed?

Hand preference in humans begins as early as in the gestational phase in the 18th week. During this stage, neurological and mental disorders can be predicted.

Hand preference of an individual, whether left-handed or right-handed is well defined at the 18th week of gestation, reveals a new study.

Analysing the characteristics of several fetal movements, the researchers have been able to accurately foresee the motor preference observed in the same boys and girls at age nine.

Left or Right Handedness is Decided When You Were a Foetus
Lefty or righty? Well it was decided when you were still in your mum's womb! A preference for the left or the right hand might be traced back to asymmetry.

‘Fetal movements can be used to identify new markers and predict any developmental problems.’

The study led by Valentina Parma, researcher at the International School for Advanced Studies - SISSA of Trieste, and Professor Umberto Castiello of the University of Padua, just published on Scientific Reports. The predictive capacity of the method used seems to be a good starting point for the early recognition of pathologies characterised by cerebral asymmetries, such as depression, schizophrenia and autism spectrum disorders.

It takes a few months for a newborn to be able to grasp an object, a few years to draw and then to write, manifesting the possible preference for the use of one hand or other parts of the body. And yet, a study just published on Scientific Reports shows that as early as in the maternal womb, hand preference is well defined and the motor system is highly sophisticated.

The researchers have studied foetal kinematics to predict manual dominance of 29 foetuses. After nine years they compared their predictions with the preference shown by the same boys and girls obtaining an accuracy that ranged between 89% and 100% depending on the parameters used.

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In particular, the researchers analysed the movements of the hands of the foetuses at the 14th, 18th and 22nd week of gestation using a 4D ultrasound scan, viewing the three dimensional image in real time and in movement, in 20-minute sessions. They studied three types of movements: two of greater precision, directed to the eyes and mouth, and one directed to the uterine wall, as a control.

The results have shown that starting from the 18th week the foetuses execute significantly more quickly the movements requiring precision with that which will become the preferred hand.