|
THE EMBRYO |
- Seen 3-7 days after
visualization of yolk sac.
- At 4 weeks and 3 days, a tiny
gestational sac becomes visible within the decidua.
- Seen transabdominally when mean sac diameter = 25mm.
- Seen transvaginally when mean sac diameter = 18mm.
- Heart rate:
- May not be seen when CRL < 5mm.
- Always seen when CRL > 5mm.
- Rate
= 70 beats per
minute at 22 days.
100-110 beats per minute at 6 weeks GA.
150-170 beats per minute at 8 weeks GA. - Crown rump length versus gestational age (Table) –
Hansemann et.al. 1979
- Crown rump length versus gestational age (Graph)– Hansemann et.al. 1979
|
Developmental
stages in human embryos |
||
|
GA (days) |
Length (mm) |
Main external characteristics |
|
34-35
|
1.5-3.0
|
Flat embryonic disk |
|
36-37
|
2.0-3.5
|
Embryo straight or slightly curved |
|
38-39
|
2.5-4.5
|
Embryo curved owing to head and tail folds |
|
40-41
|
3.0-5.0
|
Upper limb buds appear |
|
42-44
|
4.0-6.0
|
Embryo has a C-shaped curve |
|
45-46
|
5.0-7.0
|
Upper limbs are paddle shaped |
|
47-50
|
7.0-9.0
|
Hand plates formed; digital rays present. Lower
limbs are paddle shaped |
|
51-54
|
8.0-11.0
|
Foot plates formed |
|
55-57
|
11.0-14.0
|
Digital rays clearly visible in foot plates |
|
58-60
|
13.0-17.0
|
Digital rays clearly visible in foot plates |
|
61-62
|
16.0-18.0
|
Limbs extend ventrally. Trunk elongating and
straightening. Midgut herniation
prominent |
|
63-65
|
18.0-22.0
|
Upper limbs longer and
bent at elbows. Fingers webbed. |
|
66-67 |
22.0-28.0 |
Hands and feet approach
each other. Fingers are free and longer. Toes webbed. Stubby tail present.
|
|
Moore KL, Persaud TVN: Organogenic
period: the fourth to eight week. In
|
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