[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 (Biparietal Diameter): fetal biparietal diameter
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)
Appendix
Canine Reference Table
| Parameter | GS → GA | CRL → GA | HD → GA | BD → GA |
| 1 cm | 26 days | 30 days | 35 days | 36 days |
| 2 cm | 32 days | 33 days | 50 days | 43 days |
| 3 cm | 38 days | 36 days | 65 days | 50 days |
| 4 cm | 44 days | 39 days | – | 57 days |
| 5 cm | 50 days | 42 days | – | 60 days |
| 6 cm | 56 days | 45 days | – | – |
Feline Reference Table
| Parameter | BD → GA | HD → GA |
| 0.5 cm | 26 days | 15 days |
| 1 cm | 32 days | 28 days |
| 1.5 cm | 38 days | 41 days |
| 2 cm | 44 days | 53 days |
| 2.5 cm | 50 days | 66 days |
References
- Luvoni, G. C., & Grioni, A. (2000). Determination of gestational age in medium and small size bitches using ultrasonography measurement of foetal structures.
- Beccaglia, M., & Luvoni, G. C. (2006). Ultrasonographic fetal biometry in dogs and cats. Reproduction in Domestic Animals, 41(2), 136–140.
- 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.
