-
Fertilized Egg
Begins to exist when a sperm reaches the egg and burrows inside. This causes the zona pellucida to harden, preventing any other sperm from getting inside. This also causes the egg to go into Meiosis II. -
Within 24 hours of ovulation
Fertilization -
12 hours
pronuclei join together -
Zygote Stage Begins
occurs when the nuclear membrane of the ovum disappears and the two sets of chromosomes join together. -
30 to 36 hours
first round of mitosis (cleavage) -
40 hours
second round of mitosis -
50 to 60 hours
third round of mitosis -
Morula Forms
-
96 hours
64 cell embryo called a blastocyst -
Embryo Stage Begins
Occurs when the zygote begins to divide more, before implantation. -
192 hours
implantation -
192 hours
ectopic pregnancy could occur (approximate time) -
Hatching
-
288 hours
hCG begins to be secreated -
288 hours
disc with streak on the underside forms mesoderm -
336 hours
neural tube forms -
360 hours
first missed period -
504 hours
heart begins to beat, arms & legs buds appear, yolk -
816 hours
face plates forming -
816 hours
cleft lip or palate may occur -
1008 hours
muscles form, bent neck, webbed hands and feet, segmented back -
1176 hours
fingers & toes separate, eyes & ears formed -
1200 hours
genitalia begins to differentiate, eyelids fuse, amnion surrounds fetus -
1512 hours
chorionic villi sampling could be performed -
Fetal Stage Begins
Occurs when the baby begins to grow faster, bigger, and longer. Its organs also finish developing. -
2352 hours
amniocentesis could be performed -
4032 hours
eyes open, fat added under skin, head out of proportion to the body
