Dictionary TreatmentIn Vitro Fertilization (IVF)Morula Morula Reviewed by Ashley Wong, MS, Clinical Embryologist View our Editorial Policy Published: January 1, 2017 What Does Morula Mean? The morula is a stage of post-fertilization development when a fertilized egg that is known as a single-celled zygote, transitions to a mass composed of around 10-30 cells. During in vitro fertilization (IVF), the morula phase typically occurs on day 4 of development post-fertilization. The morula phase is the final phase prior to blastocyst development. Advertisement FertilitySmarts Explains Morula The primary indication of the morula phase is the presence of many cells with semi-undefined borders that are beginning to melt together. As the embryo compacts, the individual cell walls become fuzzy, creating the presence of a mass that resembles a blackberry. Morula The morula phase is the earliest period during assisted reproductive technologies (ART) that preimplantation genetic testing (PGT) or diagnostic testing is possible. This is done by removing individual cells known as blastomeres. The major stages of development of an embryo include: Zygote – a single cell that forms when sperm and egg combine Morula – forms around four days post-fertilization Blastocyst – forms around five days post-fertilization Embryo – starts the third-week post-fertilization or fifth week of pregnancy Fetus – nine weeks after conception or 11th week of pregnancy Advertisement Related Question Why did my in vitro fertilization (IVF) cycle fail? Share This Term> Related Terms Zygote Blastocyst Blastomere Hatching Blastocyst Related Reading IVF Stimulation Protocols An Intro to the In Vitro Fertilization (IVF) Process An Intro to Preimplantation Genetic Testing (PGT) Embryo Development – 6 Days in the IVF Lab Embryo and Blastocyst Grading – How Does it Work? The Surprising Fertility Advice I got from my IVF Doctor Tags Treatment In Vitro Fertilization (IVF) Embryo Development Trending Articles Pregnancy IVF Pregnancy Announcements Egg Retrieval From Eggs to Blastocysts: Understanding IVF Attrition Cervical Mucus Identifying Stages of Cervical Mucus Artificial Insemination (AI) Implantation Calendar: What is Happening During the Two Week Wait?