This **mean sac diameter calculator** is used in **obstetrics** for assessing early pregnancy development by measuring the size of the **gestational sac**, the fluid-filled structure that surrounds the embryo during the initial weeks of pregnancy.

- An ultrasound technician measures three perpendicular diameters of a gestational sac:
15mm,16mm, and17mm. The MSD Calculator averages these measurements to determine the mean sac diameter.- A doctor utilizes the
MSD Calculatorto monitor the growth of agestational sacacross multiple ultrasound appointments, ensuring proper development.

## Mean Sac Diameter Calculator

Gestational Age | Measurement 1 | Measurement 2 | Measurement 3 | Mean Sac Diameter |
---|---|---|---|---|

3 weeks | 3mm | 3mm | 4mm | 3.33mm |

4 weeks | 4mm | 5mm | 4mm | 4.33mm |

5 weeks | 6mm | 7mm | 8mm | 7mm |

5 weeks | 9mm | 8mm | 7mm | 8mm |

6 weeks | 14mm | 15mm | 16mm | 15mm |

6 weeks | 12mm | 13mm | 14mm | 13mm |

7 weeks | 22mm | 23mm | 24mm | 23mm |

7 weeks | 20mm | 21mm | 22mm | 21mm |

8 weeks | 30mm | 31mm | 32mm | 31mm |

8 weeks | 28mm | 29mm | 30mm | 29mm |

9 weeks | 38mm | 39mm | 40mm | 39mm |

9 weeks | 36mm | 37mm | 38mm | 37mm |

10 weeks | 45mm | 46mm | 47mm | 46mm |

10 weeks | 42mm | 43mm | 44mm | 43mm |

11 weeks | 50mm | 51mm | 52mm | 51mm |

11 weeks | 48mm | 49mm | 50mm | 49mm |

12 weeks | 60mm | 61mm | 62mm | 61mm |

12 weeks | 58mm | 59mm | 60mm | 59mm |

13 weeks | 65mm | 66mm | 67mm | 66mm |

13 weeks | 63mm | 64mm | 65mm | 64mm |

14 weeks | 70mm | 71mm | 72mm | 71mm |

14 weeks | 68mm | 69mm | 70mm | 69mm |

## Mean Sac Diameter Formula

The formula for calculating **Mean Sac Diameter** is:

**MSD = (Length + Width + Height) / 3**

Where:

- Length, Width, and Height are the three perpendicular measurements of the gestational sac in millimeters.

If the measurements are:

- Length:
**18mm** - Width:
**20mm** - Height:
**19mm**

`MSD = (18 + 20 + 19) / 3 = `**19mm**

## How do you calculate mean sac diameter?

- Obtain three perpendicular measurements of the gestational sac using
**ultrasound imaging**. - Ensure measurements are in millimeters.
- Add the three measurements together.
- Divide the sum by
**3**to get the average.

Ultrasound measurements:

- Measurement 1:
22mm- Measurement 2:
24mm- Measurement 3:
23mm

Calculation:

Sum:

22 + 24 + 23 = 69mmMSD:

69 / 3 = 23mm

The mean sac diameter in this case is

23mm.

## What is the mean sac diameter at 6 weeks?

At **6 weeks gestation**, the typical mean sac diameter ranges from **12 to 18 millimeters**.

A woman at exactly **6 weeks gestation** has an ultrasound. The technician measures the gestational sac:

- Measurement 1:
**14mm** - Measurement 2:
**15mm** - Measurement 3:
**16mm**

`MSD = (14 + 15 + 16) / 3 = `**15mm**

This **15mm MSD** falls within the expected range for **6 weeks gestation**.

## What is the mean sac diameter at 5 weeks?

At **5 weeks gestation**, the mean sac diameter typically ranges from **5 to 10 millimeters**.

A woman believed to be **5 weeks pregnant** undergoes an ultrasound. The gestational sac measurements are:

- Measurement 1:
**7mm** - Measurement 2:
**8mm** - Measurement 3:
**7mm**

`MSD = (7 + 8 + 7) / 3 = `**7.33mm**

This **MSD of 7.33mm** is consistent with a **5-week gestation**.

## What is the mean sac diameter of a miscarriage?

- An
**empty gestational sac**measuring >**25mm** - A sac that doesn’t grow appropriately between scans
- A sac that’s significantly smaller than expected for the gestational age

A woman at **7 weeks gestation** has an ultrasound showing:

- Measurement 1:
**10mm** - Measurement 2:
**11mm** - Measurement 3:
**10mm**

`MSD = (10 + 11 + 10) / 3 = `**10.33mm**

This **MSD** is considerably smaller than the expected **20-30mm** for **7 weeks**, potentially indicating a **non-viable pregnancy**.

## What is the diameter of the sac at 3 weeks?

At **3 weeks post-conception** (considered **5 weeks gestation** due to pregnancy dating), at this early stage is usually between **2-4 millimeters**.

An early ultrasound at **3 weeks post-conception** shows:

- Measurement 1:
**3mm** - Measurement 2:
**3mm** - Measurement 3:
**4mm**

`MSD = (3 + 3 + 4) / 3 = `**3.33mm**

This **MSD of 3.33mm** is consistent with very early pregnancy development.

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