At first pregnancy check up i found out i had 2 horns then after a c-section i found out both uteruses was only half size. what is the cause of this?

Bicornuate uterus: is a type of congenital uterine duplication anomaly. It results from an abnormal development that results in a uterus divided into two horns from a partial failure of fusion. Infertility is not usually a problem with this type of malformation because implantation of the embryo is not impaired. The most common symptomatic presentation is with early pregnancy loss and cervical incompetence.