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Fertilized Egg
Begins to exist when a sperm fertilizes the egg. -
Start
Fertilization -
Hour 12
Joining of Pronuclei -
Zygote Stage Begins
Occurs when the two pronuclei join together. -
Hours 30-36
1st Round of Mitosis (Cleavage); 2 cells -
Hour 40
2nd Round of Mitosis; 4 cells -
Hours 50-60
3rd Round of Mitosis; 8 cells -
Morula
16 cells -
Embryo Stage Begins
Occurs when the zygote becomes a morula. -
Days 8-10
Implantation -
Day 4
64 cell Embryo called a Blastocyst -
Hatching
Cells break through hard zona pellucida -
Day 10
Ectopic pregnancy could occur (approximate time) -
Day 12
hCG begins to be secreted -
Day 12
Disc with streak on the underside forms the mesoderm -
Day 14
Neural tube forms -
Day 15
1st missed period -
Day 21
Heart begins to beat, arm and leg buds appear, yolk sac makes RBCs -
Days 34-36
Face plates forming -
Days 34-36
Cleft lip or palate may occur -
Week 6
Muscles form, bent neck, webbed hands and feet, segmented back -
Week 7
Fingers and toes separate, eyes and ears formed -
Fetal Stage Begins
Occurs when all the organs are formed. -
Day 50
Genitalia begin to differentiate, eyelids fuse, amnion surrounds fetus -
Weeks 9-11
Chorionic villi sampling could be performed -
Week 14-15
Amniocentesis could be performed -
Months 6-7
Eyes open, fat added under skin, head out of proportion to the body
