[Glossary] OB calculations

• GA: Gestational Age.
• Fetal age: Conceptional age.
• EFW: Estimated fetal weight.
• AUA: Arithmetic ultrasound age.
• DOC: Date of conception.
• LMP: Last menstrual period.
• EDD: Estimated due date.

In Early OB

• CRL: Crown-rump length
• GS: Gestational sac.
• NT: Nuchal Translucency
• IT: Intracranial Translucency

In Mid-late OB

• AC: Abdominal circumference.
• HC: Head circumference.
• FL: Femur length.
• BPD: Biparietal diameter.
• AFQ: Amniotic Fluid Quadrants
  • Q1
  • Q2
  • Q3
  • Q4
• TCD: Transcerebellar Diameter
• IOD: Interorbital Distance
• OOD: Outer Orbital Distance
• CM: Cisterna Magna 
• TL: Tibia Length
• FIB: Fibula Length
• HL: Humerus Length
• RAD: Radius Length
• UL: Ulna Length
• LVD: Lateral Ventricle Diameter
• NF: Nuchal Fold Thickness
• AF-SDP Amniotic Fluid – Single Deepest Pocket
• CxL: Cervical Length

Formulas

• GS, CRL, BPD, HC, AC, FL These GA values are determined based on the mapping table provided in the appendix below.
• TCD: GA(Weeks) = 4.9 + 0.5 × TCD(mm)
• TL: GA(Weeks) = 2.7 × TL(cm) + 8.7
• FIB: GA(Weeks) = 2.7 × FIB(cm) + 8.6
• HL: GA(Weeks) = 2.5 × HL(cm) + 9.0
• RAD: GA(Weeks) = 2.6 × RAD(cm) + 9.0
• UL: GA(Weeks) = 2.6 × UL(cm) + 9.2
• EDD = Exam Date + (280 – GA) Days

References

1. Early OB calculations: Hadlock 1992.
   Fetal Crown-Rump Length: Reevaluation of Relation to Menstrual Age with High-Resolution Real-Time US.
2. Mid-late OB calculations:
   1. Hadlock 1984
      Hadlock F.P, Deter R.L, Harrist R.B. and Park S.K, Estimating fetal age: computer-assisted analysis of multiple fetal growth parameters, Radiology, 152, pp 497-501, 1984
   2. Goldstein 1987, Ultrasound Obstet Gynecol 7:161–165
   3. Chitty 1994, Ultrasound Obstet Gynecol 4:287–296
   4. Jeanty 1984, Radiology 151:417–422
3. EFW equations
   EFW by AC, BPD FL, and HC: Hadlock 1985
   Hadlock F.P, Harrist R.B, Sharman R.S, Deter R.L, Park S.K, Estimation of fetal weight with the use of head, body, and femur measurements–a prospective study, Am.J.Obstet.Gynecol., 151, pp 333-337, 1985

Appendix Tables