[Glossary] Veterinary OB Calculations

• GA (Gestational Age): number of days of pregnancy (from conception/ovulation to the examination day)
• EDD (Estimated Due Date): predicted date of parturition
• DOC (Date of Conception): date of conception or mating
• GS (Gestational Sac Diameter): mean diameter of the gestational sac
• CRL (Crown-Rump Length): length from crown to rump
• HD (Head Diameter): fetal head diameter
• BD/BPD (Biparietal Diameter): fetal biparietal diameter
• CD (Conceptus Diameter): diameter of the embryonic vesicle/embryo
• EOD (Eye Orbit Diameter): transverse diameter of the fetal eye orbit

Canine (Dogs)

• Average gestation length: 63 days from ovulation
• Formulas:
  • GS: GA = 6 × GS (cm) + 20
  • CRL: GA = 3 × CRL (cm) + 27
  • HD: GA = 15 × HD (cm) + 20
  • BD: GA = 7 × BD (cm) + 29
  • HD + BD: GA = 6 × HD (cm) + 3 × BD (cm) + 30
• EDD calculation: EDD = Date of examination + (63 − GA)

Feline (Cats)

• Average gestation length: 65 days from ovulation
• Formulas:
  • BD: GA = 11 × BD (cm) + 21
  • HD: GA = 25 × HD (cm) + 3
• EDD calculation: EDD = Date of examination + (65 − GA)

Bovine

• Average gestation length: 280 days from ovulation
  • FormBD/BPD: GA = 14.5 + 2.2 × BPD(mm)
  • CRL: GA = 18.5 + 1.7 × CRL(cm)
• EDD calculation: EDD = Date of examination +  (280 − GA)

Ovine

• Average gestation length: 150 days from ovulation
• Formulas:
  • BD/BPD: GA = 14.5 + 2.2 × BPD(mm)
  • CRL: GA = 18.5 + 1.7 × CRL(cm)
• EDD calculation: EDD = Date of examination + (150 − GA)

Porcine

• Average gestation length: 114 days from ovulation
  • FormBD/BPD: GA = 15.3 + 2.1 × BPD(mm)
  • CRL: GA = 17.0 + 1.8 × CRL(cm)
• EDD calculation: EDD = Date of examination + (114 − GA)

Equine

• Average gestation length: 340 days from ovulation
• Formulas:
  • CD: GA = 25.0 + 1.7 × CD(mm)
  • EOD: GA = 45.3 + 3.0 × EOD(mm)
• EDD calculation: EDD = Date of examination + (340 − GA)

Appendix 

Canine Reference Table

Feline Reference Table

Bovine Reference Table

Ovine Reference Table

Porcine Reference Table

Equine Reference Table

References

1. Luvoni, G. C., & Grioni, A. (2000). Determination of gestational age in medium and small size bitches using ultrasonography measurement of foetal structures.
2. Beccaglia, M., & Luvoni, G. C. (2006). Ultrasonographic fetal biometry in dogs and cats. Reproduction in Domestic Animals, 41(2), 136–140.
3. Yeager, A. E., Mohammed, H. O., Meyers-Wallen, V. N., Vannerson, L., & Concannon, P. W. (1992). Ultrasonographic appearance of the uterus, placenta, fetus, and fetal membranes throughout accurately timed pregnancy in Beagles. American Journal of Veterinary Research, 53(3), 342–351.
4. Kähn, W. (1992). Veterinary reproductive ultrasonography. Mosby-Year Book, St. Louis.
5. Haibel, G. K. (1988). Real-time ultrasonic fetal head measurements and gestational age in cattle. Theriogenology, 30(5), 905–913.
6. Haibel, G. K. (1990). Use of ultrasonography in reproductive management of sheep and goats. Veterinary Clinics of North America: Food Animal Practice, 6(3), 597–613.
7. Haibel, G. K. (1988). Ultrasonic fetal measurements in swine. Theriogenology, 29(1), 215–223.
8. Martinat-Botté, F., Bariteau, F., Forgerit, Y., & Terqui, M. (2000). Ultrasonography and reproduction in female pigs. INRA Productions Animales, 13(1), 23–33.
9. Curran, S., & Ginther, O. J. (1991). Ultrasonic determination of equine fetal age. Theriogenology, 36(3), 449–460.
10. Renaudin, C. D., Gillis, C. L., Tarantal, A. F., & Ginther, O. J. (1997). Ultrasonographic determination of fetal age in horses using eye orbit diameter. Theriogenology, 47(3), 673–680.