Mean Sac Diameter Calculator
Calculate gestational age from ultrasound measurements of the gestational sac
Calculate Mean Sac Diameter
Maximum diameter measurement on ultrasound
Perpendicular to length measurement
Anteroposterior dimension measurement
Example Calculation
Early Pregnancy at 6 Weeks
Gestational sac measurements:
• Length: 12.5 mm
• Width: 11.8 mm
• Height: 13.2 mm
Mean sac diameter: (12.5 + 11.8 + 13.2) ÷ 3 = 12.5 mm
Result
Gestational age: 12.5 + 30 = 42.5 days ≈ 6w 1d
Assessment: Early pregnancy progressing normally
Accuracy range: 5w 3d - 6w 6d (±5 days)
Gestational Sac Milestones
Gestational Sac
First visible structure
Usually appears around 5 weeks
Yolk Sac
Secondary structure
Appears around 5.5-6 weeks
Embryo
Fetal pole visible
Usually visible by 6-7 weeks
Cardiac Activity
Heartbeat detectable
Usually by 6-8 weeks
MSD Reference Guide
Measurement Tips:
- • Use transvaginal ultrasound for better accuracy
- • Measure the largest diameter in each plane
- • Ensure clear gestational sac borders
- • Take multiple measurements and average
Understanding Mean Sac Diameter
What is the Gestational Sac?
The gestational sac is the first structure visible during early pregnancy ultrasound. It appears as a white rim around a clear center and contains the developing embryo, yolk sac, and amniotic fluid. The gestational sac is typically visible around 5 weeks of pregnancy.
Clinical Applications
- •Early pregnancy dating before crown-rump length is measurable
- •Confirming intrauterine pregnancy location
- •Assessing early pregnancy viability
- •Monitoring pregnancy progression in first trimester
Measurement Technique
MSD = (Length + Width + Height) ÷ 3
Gestational Age = MSD + 30 days
- Length: Largest diameter measurement
- Width: Perpendicular to length
- Height: Anteroposterior dimension
Ultrasound Considerations
Important: After 10 weeks gestation, crown-rump length (CRL) becomes more accurate for pregnancy dating than mean sac diameter.