Ever heard of a Zona-Free Embryo? 😱 Occasionally, an embryo grows and a zona pellucida never forms. It is unsure why this happens, but doesn't always mean the embryo won't continue to grow and implant! 🤰 What is the zona pellucida? The zona is the strong membrane that forms around an ovum as it develops in the ovary. The membrane remains in place during the egg's travel through the fallopian tube. To fertilize the egg, a sperm must penetrate the thinning zona pellucida. The zona continues to s