The zona pellucida (ZP) is the outermost layer of egg cells. In other words, it is the first membrane sperm have to cross in order to join the egg cell and fertilize it.
By Dra. Laura de la Fuente Bitane (gynecologist), Zaira Salvador BSc, MSc (embryologist) and Romina Packan (invitra staff).
Last Update: 11/29/2018