Could you provide sample embryogenesis questions for obstetrics students?

Sample Embryogenesis Questions for Obstetrics Students

I can provide educationally valuable sample questions covering key embryogenesis concepts relevant to obstetrics practice, drawing from current understanding of early human development.

Blastocyst Formation and Early Development

Question 1: Timeline and Cellular Changes

• A patient asks when her fertilized egg becomes capable of forming different tissue types. At what point post-fertilization do cells transition from totipotent to pluripotent, and what structure characterizes this transition? 1
  • Answer: Approximately 4 days post-fertilization, when the blastocyst forms with distinct trophectoderm (outer layer) and inner cell mass (pluripotent cells)

Question 2: Blastocyst Structure

• Describe the three founding lineages present in a human blastocyst by day 5-6 post-fertilization and their eventual fates. 2
  • Answer: Trophectoderm (forms placental structures), epiblast (forms embryo proper), and primitive endoderm (forms extraembryonic structures like yolk sac)

Implantation Window and Maternal-Embryonic Interaction

Question 3: Window of Implantation

• A fertility specialist is planning embryo transfer timing. What is the optimal window for blastocyst implantation, and what maternal endometrial changes define this period? 3, 4
  • Answer: Luteal days +3 to +5 (or LH day +6 to +10 for natural cycles); characterized by decidualization with pinopode formation and progesterone-primed receptive endometrium

Question 4: Embryo-Endometrial Crosstalk

• What embryo-secreted factors facilitate successful implantation and maternal recognition of pregnancy? 3
  • Answer: Chorionic gonadotropin (CG), interleukin-1β (IL-1β), and factors that induce local trophectoderm maturation for directional attachment

Gastrulation and Germ Layer Formation

Question 5: Primitive Streak Formation

• At what developmental timepoint does the primitive streak form, and why is this stage significant for both embryonic development and research ethics? 5
  • Answer: Around day 14 post-fertilization; marks the beginning of gastrulation, body axis formation, and the point after which twinning is no longer possible—historically the "14-day rule" limit for embryo research

Question 6: Germ Layer Derivatives

• Which embryonic structure gives rise to the definitive gut endoderm, and what is a common misconception about trophoblast contribution? 6
  • Answer: The epiblast (through gastrulation) forms definitive endoderm; trophoblast forms only extraembryonic/placental tissues, NOT gut endoderm

Clinical Correlations and Pregnancy Loss

Question 7: Early Pregnancy Loss

• A couple experiences recurrent first-trimester loss. During which developmental window is pregnancy loss most common, and what embryonic processes occur during this vulnerable period? 5, 1
  • Answer: Between weeks 2-4 post-fertilization (gestational weeks 4-6); encompasses implantation, extraembryonic tissue development, early gastrulation, and primitive streak formation

Question 8: Congenital Malformations

• Neural tube defects and cardiac malformations have their origins in which developmental stage, and approximately when does this occur? 5
  • Answer: During and after primitive streak formation through early organogenesis (approximately day 14-30 post-fertilization, Carnegie stage 12); requires understanding of nervous system and heart development during gastrulation

Advanced Concepts: Embryo Models and Research

Question 9: Stem Cell-Derived Embryo Models

• What are "blastoids," and how do they differ from actual human embryos in terms of research applications and ethical considerations? 5, 2, 7
  • Answer: Stem cell-derived structures that model blastocyst development with >97% efficiency in forming the three founding lineages; not considered equivalent to human embryos under most legislation, allowing study beyond traditional 14-day limits

Question 10: Species-Specific Development

• Why is extrapolation from mouse embryo studies to human development problematic? Provide a specific example. 5
  • Answer: Species-specific differences exist; for example, humans have yolk sac trophoblast tissue that could not have been predicted from mouse models, discovered only through human embryo culture studies

Ultrasound and Clinical Detection

Question 11: Early Ultrasound Findings

• What is the earliest ultrasound finding in pregnancy, and when is it typically visible? 1
  • Answer: Gestational sac, visible approximately 4-5 weeks after last menstrual period (2-3 weeks post-fertilization)

Question 12: Biochemical Confirmation

• What laboratory finding confirms ovulation has occurred, and when should it be measured? 1
  • Answer: Mid-luteal phase progesterone ≥5 ng/mL (≥16 nmol/L), measured around cycle day 21 in a 28-day cycle