Mean Sac Diameter Calculator

Mean Sac Diameter Calculator

To determine Mean Sac Diameter (MSD), input perpendicular measurements of gestational sac: Length, Width, and Height in millimeters (mm) in calculator.

The calculator automatically averages these measurements to calculate MSD, which is used to estimate gestational age and assess early pregnancy development.

Enter accurate ultrasound measurements for the most precise results.

Mean Sac Diameter Chart By Week (MM)

Gestational Age (Weeks)Mean Sac Diameter (MSD) (mm)
42-3
4.53-5
55-7
5.57-10
610-14
6.514-17
717-20
7.520-23
823-25
8.525-28
928-31
9.531-34
1034-37

How to Calculate Mean Sac Diameter?

To calculate Mean Sac Diameter, take three perpendicular measurements of the gestational sac during an ultrasound examination. Measure longest dimension of the gestational sac for length, then measure widest point perpendicular to length for width, and finally measure vertical dimension perpendicular to both length and width for height.

All measurements should be taken in millimeters (mm) for accuracy. These three measurements are then averaged to determine the Mean Sac Diameter.

Formula for Mean Sac Diameter

Basic MSD Formula:

Mean Sac Diameter (mm) = (Length + Width + Height) ÷ 3
Where:
L = Length of the sac
W = Width of the sac
H = Height of the sac

Gestational Age Estimation:

Gestational Age (weeks) = (MSD in mm + 30) ÷ 7
Where:
MSD = Mean Sac Diameter in millimeters

Expected hCG Levels:

Minimum Expected hCG (mIU/ml) = 2000 × e^(0.3 × MSD in mm)
Where:
MSD = Mean Sac Diameter in millimeters
e = Euler’s number (approximately 2.71828)

Example 1: Early Gestational Sac

  • Face Length = 8 mm
  • Face Width = 7 mm
  • Face Height = 7 mm
  • MSD = (8 + 7 + 7) ÷ 3 = 7.33 mm
  • Gestational Age = (7.33 + 30) ÷ 7 = 5.3 weeks

Example 2: Normal Development

  • Face Length = 15 mm
  • Face Width = 14 mm
  • Face Height = 13 mm
  • MSD = (15 + 14 + 13) ÷ 3 = 14 mm
  • Gestational Age = (14 + 30) ÷ 7 = 6.3 weeks

Example 3: Larger Gestational Sac

  • Face Length = 20 mm
  • Face Width = 19 mm
  • Face Height = 18 mm
  • MSD = (20 + 19 + 18) ÷ 3 = 19 mm
  • Gestational Age = (19 + 30) ÷ 7 = 7 weeks

Example 4: Asymmetric Sac

  • Face Length = 16 mm
  • Face Width = 12 mm
  • Face Height = 14 mm
  • MSD = (16 + 12 + 14) ÷ 3 = 14 mm
  • Gestational Age = (14 + 30) ÷ 7 = 6.3 weeks

Example 5: Small Gestational Sac

  • Face Length = 6 mm
  • Face Width = 5 mm
  • Face Height = 5 mm
  • MSD = (6 + 5 + 5) ÷ 3 = 5.33 mm
  • Gestational Age = (5.33 + 30) ÷ 7 = 5.0 weeks

What is Mean Sac Diameter?

Mean Sac Diameter (MSD) is a measurement used in early pregnancy assessment that represents the average size of the gestational sac, calculated by taking the mean of three perpendicular dimensions: length, width, and height. This measurement is typically performed during ultrasound examinations between 4-8 weeks of gestation to estimate gestational age and assess early pregnancy development.

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