Early fetal development

Question 1

Day 0

Answer 1

Fertilization by sperm, forming zygote, initiating embryogenesis

*egg is in metaphase II before it is fertilized

Question 2

Within week 1

Answer 2

*hCG secretion begins around the time of implantation of blastocyst.

“Blastocyst “sticks” at day 6”

Day 3 Morula (32 cells)

Question 3

Within week 2

Answer 3

Bilaminar disc (*epiblast, *hypoblast).

“2 weeks = 2 layers”

Question 4

Within week 3

Answer 4

*Gastrulation forms *trilaminar embryonic disc

Cells from epiblast invaginate–>primitive streak–>endoderm, mesoderm, ectoderm

• Neuralation (by shh)
• Notochord arises from midline *mesoderm

overlying *ectoderm becomes *neural plate

“3 weeks = 3 layers”

Question 5

Weeks 3–8

Answer 5

embryonic period

• Neural tube formed by *neuroectoderm and closes by week 4.
• Organogenesis
• Extremely susceptible to teratogens

Question 6

Week 4

Answer 6

Heart begins to beat

Upper and lower limb buds begin to form

“4 weeks = 4 limbs and 4 heart chambers”

Question 7

Week 6

Answer 7

Fetal cardiac activity visible by transvaginal ultrasound.

Question 8

Week 8

Answer 8

Fetal movements start

Gait at week 8

Question 9

Week 10

Answer 9

Genitalia have male/female characteristics

*16-19 weeks U/S in clinic