1. What is the Gestational Sac Calculator?

The Gestational Sac Calculator estimates gestational age from the mean sac diameter (MSD) measured during early pregnancy ultrasound. This formula provides a quick assessment of pregnancy dating in the first trimester.

2. How Does the Calculator Work?

The calculator uses the gestational age formula:

Where:

• \( MSD \) — Mean sac diameter (mm)
• \( GA \) — Gestational age (weeks)

Explanation: The formula provides a simple linear relationship between sac size and gestational age, useful for early pregnancy dating before fetal structures are visible.

3. Importance of Gestational Age Calculation

Details: Accurate gestational age estimation is crucial for appropriate pregnancy management, determining expected due date, and monitoring fetal development milestones.

4. Using the Calculator

Tips: Enter mean sac diameter in millimeters (mm) as measured by ultrasound. The measurement should be taken in the first trimester, typically between 5-10 weeks gestation.

5. Frequently Asked Questions (FAQ)

Q1: When is this calculation most accurate?
A: This formula is most accurate in very early pregnancy, typically between 5-7 weeks gestation, before fetal pole is visible.

Q2: What if the fetal pole is visible?
A: Once the fetal pole is visible, crown-rump length (CRL) measurement provides a more accurate estimate of gestational age.

Q3: How is MSD measured?
A: MSD is calculated by averaging three orthogonal measurements of the gestational sac (length, width, and height) taken during ultrasound examination.

Q4: Are there limitations to this calculation?
A: This formula becomes less accurate after 7-8 weeks and should not be used once fetal structures are visible. Irregular sac shape can also affect accuracy.

Q5: What is the normal range for MSD?
A: Typically, the gestational sac becomes visible at around 4.5-5 weeks with MSD of 2-3mm, and grows approximately 1mm per day in early pregnancy.