Mean Sac Diameter (MSD) Calculator

Your details

Choose whether to enter the three raw ultrasound measurements or a pre-calculated MSD.
Select the unit used on your ultrasound report. Results are always shown in mm.
The longest dimension of the gestational sac, as measured on ultrasound.
mm
The width of the gestational sac in the second perpendicular plane.
mm
The height (depth) of the gestational sac, the third perpendicular plane.
mm
Enter the date of the ultrasound scan to calculate an estimated due date.
Mean sac diameterFirst trimester sac (5 - 10 weeks)
18mm

Average of the three perpendicular sac measurements

Gestational age6 weeks 6 days
Typical range (+/- 5 days)6 weeks 1 day to 7 weeks 4 days
18 mm
Before 5 weeks<105 to 6 weeks10-176 to 7 weeks17-277 to 9 weeks27-389+ weeks38+

MSD of 18.0 mm corresponds to approximately 6 weeks 6 days of pregnancy.

  • The gestational sac grows approximately 1 mm per day in early pregnancy, which is the basis of the MSD + 30 formula.
  • At 6 weeks or later, a yolk sac should normally be visible inside the gestational sac. Its absence may prompt clinical follow-up.
  • By about 6.5 weeks, a fetal pole with cardiac activity is usually detectable. If one is visible, crown-rump length (CRL) measurement gives more accurate dating than MSD.
  • MSD-based dating carries a typical uncertainty of plus or minus 5 days. After a fetal pole is visible, CRL is the preferred method for estimating gestational age.

Next stepDiscuss the result with your healthcare provider. If a fetal pole is visible, ask for CRL measurement to refine your due date.

 = Powered by OnlyCalculators