Pre-embryonic period

Question 1

define pre-embryonic, embryonic and fetal periods

Answer 1

pre-embryonic = first two weeks 
embryonic = 3-8 weeks 
fetal = 9 to birth

Question 2

Give the key events in the first week

Answer 2

fertilisation in the ampulla
cleavage to form tow blastomeres and a zona pellucida
formation of the morula - 16 totipotent cells
compaction forming the inner and out cell masses and the blastocyst cavity = blastocyst
hatching
implantation

Question 3

give the key events of the second week

Answer 3

differentiation of the inner and outer cell masses
completion of implantation establishing the maternal blood flow, maternal-fetal exchange, rapid development of the syncytiotrophoblast = lacunae and embryonic pole and the primitive yolk sac forms
formation of extraembryonic mesoderm
uteroplacental ciruclation begins as maternal sinusoids invaded by syncytiotrophoblast
formation of secondary yolk sac
formation of chorionic cavity and convective stalk

Question 4

give four (two key ones) conditions liked to implantation defects

Answer 4

key ones - ectopic pregnancy
fertilisation occurs in fallopian tube
placenta praevia
implantation in lower uterine segment

IUGR and pre-eclampsia

Question 5

when is pre implantation genetic diagnosis used

Answer 5

when cells are totipotent

a cell can be safely removed from morula and tested for serious heritable conditions prior to transfer of embryo into the mother.