The embryo - Ultrasound in early pregnancy

The embryo

• Detectable at ~37 days from LMP by TV scan as a bright linear echo adjacent to the yolk sac. 

CRL ~2mm and cardiac activity can be identified

• Embryo grows at ~1mm per day

• All viable embryos with CRL >7mm should demonstrate cardiac activity



• In asymptomatic women, the risk of miscarriage is :

12% when an empty sac is identified by ultrasound, 
7.2% when a live embryo with CRL <5mm is detected, 
3.3% for embryos of 6-10mm and 
0.5% with a live embryo with CRL >10mm is detected

• Embryonic heart rate increases between 6-9 weeks followed by a slight decline after 10 weeks.

 • The biological variability of CRL is small and growth is rapid - it is therefore the most accurate ultrasound estimate of gestation age

• In multiple pregnancies, the larger CRL should be used for assigning gestation age