Pressure on the fingers from the baby touching, and their surroundings create what are called "friction ridges", the faint lines you see on your fingers and toes. These ridges are completely formed by the time a fetus is 6 months old, that's 3 months before the baby is born!

At what age are fingerprints formed?

These folds eventually cause the surface layers of the skin to fold too, and by the time a fetus is 17 weeks old – about halfway through a pregnancy – its fingerprints are set.

Are fingerprints formed before or after birth?

Fingerprints begin appearing during the phases of fetal development and continue transforming and developing as the baby does. They end up being a unique pattern of arches, bridges, whirls, and loops by the end of those 9 months.