Early Pregnancy Ultrasound

Here's an article I found at http://radiopaedia.org/articles/early-pregnancy that I'm saving here for reference later.

Early pregnancy

A.Prof Frank Gaillard◉ et al.

Early pregnancy roughly spans the first ten weeks of the first trimester.

Radiographic features

Antenatal ultrasound 

• 0-4.3 weeks: no ultrasound findings
• 4.3-5.0 weeks: 
  • possible small gestational sac
  • possible double decidual sac sign (DDSS)
  • possible intradecidual sac sign (IDSS)
• 5.1-5.5 weeks:
  • ​gestational sac should be visible by this time
• 5.5-6.0 weeks 
  • yolk sac should be visible by this time
  • gestational sac should be ~6 mm in diameter
  • double bleb sign
• >6.0 weeks
  • fetal pole may be identifiable on endovaginal ultrasound (1-2 mm)
  • fetal heart rate (FHR) should be ~100-115 bpm
  • gestational sac should be ~10 mm in diameter
• 6.5 weeks
  • crown rump length (CRL) should be ~5 mm
• 7-8 weeks
  • CRL is between 11-16 mm
  • cephalad and caudal poles can be identified
• 8-9 weeks
  • CRL is between 17-23 mm
  • limb buds appear
  • head can be seen as separate from the body
• 9-10 weeks
  • CRL is between 23-32 mm
  • fetal heart rate 170-180 bpm
  • fetal movement can be seen
  • a round hypoechoic structure in the fetal brain represents a developingembryonic/fetal rhombencephalon
  • nuchal translucency may begin to be seen

Transvaginal/endovaginal (TV/EV) scanning

• intradecidual sac sign (IDSS): early sign on a TV scan
• when the MSD measures 25 mm, an embryo must be visible
• when the CRL measures >7 mm, an embryo must show cardiac activity
• an embryo should be seen <=14 days after a scan with a gestational sac without ayolk sac
• an embryo should be seen <=11 days after a scan with a gestational sac and a yolk sac

Transabdominal (TA) scanning

• when the MSD measures 20 mm a yolk sac should be visible
• when the MSD measures 25 mm, an embryo must be visible