What is the preimplantation embryo stage occurring around day 5-6 after fertilization, characterized by a blastocoele, trophectoderm, and inner cell mass?

What is the preimplantation embryo stage occurring around day 5-6 after fertilization, characterized by a blastocoele, trophectoderm, and inner cell mass?

• A. Biochemical pregnancy
• B. Birth (single)
• C. Blastomere
• D. Blastocyst

Answer: (D)

Blastocyst is the stage described. Around day 5–6 after fertilization, the embryo forms a hollow ball with a fluid-filled cavity called the blastocoel, an outer layer of cells called the trophectoderm, and an inner cell mass that will become the embryo. This configuration shows the transition from early cleavage to an implantation-ready structure. The blastocyst is what implants into the uterine lining soon after this stage. A blastomere is an earlier cleavage-stage cell, so it doesn’t describe the day-5–6 structure; a biochemical pregnancy refers to hormone evidence of pregnancy rather than a developmental stage; birth occurs long after implantation.

Blastocyst is the stage described. Around day 5–6 after fertilization, the embryo forms a hollow ball with a fluid-filled cavity called the blastocoel, an outer layer of cells called the trophectoderm, and an inner cell mass that will become the embryo. This configuration shows the transition from early cleavage to an implantation-ready structure. The blastocyst is what implants into the uterine lining soon after this stage. A blastomere is an earlier cleavage-stage cell, so it doesn’t describe the day-5–6 structure; a biochemical pregnancy refers to hormone evidence of pregnancy rather than a developmental stage; birth occurs long after implantation.