Transabdominal
    3600iu BhCG [VGH]- gest sac visualized
    20mm mean gestational sac diameter (MSD) - yolk sac seen
    25mm MSD - embryo seen
    9mm CRL embryo - heart activity, 6.9wks
       6w 90-110bpm
       9w 140-170bpm
Transvaginal
    1000iu BhCG - gest sac visualized, earliest poss at 500iu
    8mm MSD - yolk sac seen
    15mm MSD - embryo seen
    6mm embryo -must have heart activity, 6.3wks
    Heart Rate < 85bpm at < 10wks gest = demise
    Age in days = sac diameter in mm + 33
    Age in days = CRL (mm) + 42
    Age in wks = CRL in cm + 6.5
   
Average growth in MSD = 1.1mm/day for 5<wks>8

Biparietal Diameter - transverse at cavum sep, thalmi & choroid
2.0cm @ 12wk +/- 1.0wks
4.8cm @ 20wk
7.6cm @ 30wk +/- 2.0wks
9.5cm @ 40wk

Head Circumference
shape independent, more accurate overall
ease of measurement also makes it a good parameter
Most useful as a comparison with AC to asses fetal well being
HC/AC 1.2 @ 16wks
1.0 @ 36wks

Abdominal Circumference
axial at umbilical part of L portal
also thru stomach, traced at outer margin
distortion poss w transducer, contraction, oligo etc
most variable parameter, susceptable to growth delay change
10.0cm @ 16wks +/- 1.9wks
15.0cm @ 20wks +/- 2.0wks
26.0cm @ 30wks +/- 2.2wks
36.0cm @ 40wks +/- 2.5wks

Femur Length
measured ends of bone should be blunt
epiphysis should not be included
bowing seen with osteogenesis imperfecta, dwarfism, hypophos etc
fractures can also preclude use as measurement for age
20mm @ 16wks +/- 3wks
32mm @ 20wks
57mm @ 30wks
80mm @ 40wks +/- 2wks

 

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