What is the Zona pellucida?

The zona pellucida (ZP), also known as the pellucid layer, consists of the translucent membrane that surrounds the egg. Only a sperm will be able to pass through this layer to fertilize the egg and result in pregnancy.

Another function of the pellucid layer of the oocyte is to control the first divisions that occur in the embryo. This layer is present in the embryo until it reaches the blastocyst stage, that is, until it is at day 5 of development.