WEEK 6 OF GESTATION
Length = 5 - 5.5mm and it can be constantly seen as separate from the yolk sac.
Gestational Sac = 15.5mm in diameter.
Normal video at 6 weeks of gestation.
ULTRASOUND
Amnion first visualized.
Anechoic unpartitioned telencephalon and mesencephalic vesicles present.
Early embryonic motion (trunk flexion) can be seen.
Limb buds not reliably seen.
Heart
Active slow pulsations (100-110 bpm).
Two chambered heart.
All embryos should have visible cardiac activity.
Cranium
Only one cavity recognizable = rhombencephalic cavity.
Always visible from 7 weeks 0 days onwards.
In embryos up to 16mm, CRL grows faster than rhombencephalon (this results in a relative but not actual decrease in the size of the rhombencephalon).