Some researchers hypothesize, from the early development stages of humans, that clubfoot is formed by a malfunction during gestation. Amniocentesis is believed to increase the rates of this deformity because there is an increase in possible amniotic leakage during the procedure.[citation needed] Underdevelopment of the bones and muscles in the embryonic foot may be another underlying cause. Underdevelopment prevents the fetus's foot from rotating medially, leaving it in the club formation after birth.