Rule of hasse FMT
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Hasse's rule estimates fetal intrauterine age from the crown-heel length (CHL).
[
\text{Fetal age in months} = \sqrt{\text{Crown-heel length in cm}}
]
Example:
CHL = 16 cm
CHL = 16 cm
[
\sqrt{16} = 4
]
So the fetal age is approximately 4 months.
It is chiefly used for fetuses in the first 5 months. For later pregnancy, Morrison's rule is used:
[
\text{Age in months} = \frac{\text{CHL in cm}}{5}
]
Example: 40 cm ÷ 5 = 8 months.
Source: P C Dikshit Textbook of Forensic Medicine and Toxicology, determination of intrauterine age.
Source: P C Dikshit Textbook of Forensic Medicine and Toxicology, determination of intrauterine age.
Explain Hasse’s rule with fetal-length examples
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Hasse's rule for estimating fetal age from length
Hasse's rule uses the crown-heel length (CHL), measured from the top of the head to the heel, in centimetres.
1. First 5 fetal months
[
\text{CHL (cm)} = (\text{age in months})^2
]
Therefore:
[
\text{Age in months} = \sqrt{\text{CHL in cm}}
]
| Crown-heel length | Calculation | Estimated fetal age |
|---|---|---|
| 1 cm | √1 | 1 month |
| 4 cm | √4 | 2 months |
| 9 cm | √9 | 3 months |
| 16 cm | √16 | 4 months |
| 25 cm | √25 | 5 months |
Example: A fetus has a crown-heel length of 16 cm.
[
\sqrt{16}=4
]
Estimated intrauterine age = 4 months.
2. Last 5 fetal months
After the fifth month, length increases approximately by 5 cm each month:
[
\text{CHL (cm)} = \text{age in months} \times 5
]
Therefore:
[
\text{Age in months} = \frac{\text{CHL in cm}}{5}
]
| Crown-heel length | Calculation | Estimated fetal age |
|---|---|---|
| 30 cm | 30 ÷ 5 | 6 months |
| 35 cm | 35 ÷ 5 | 7 months |
| 40 cm | 40 ÷ 5 | 8 months |
| 45 cm | 45 ÷ 5 | 9 months |
| 50 cm | 50 ÷ 5 | 10 months / term |
Example: A fetus has a crown-heel length of 40 cm.
[
40 \div 5=8
]
Estimated intrauterine age = 8 months.
Easy memory aid
- Months 1 to 5: square the month
4 months → (4^2 = 16) cm - Months 6 to 10: multiply the month by 5
8 months → (8 \times 5 = 40) cm
This is an approximate forensic method, and individual fetal growth variation limits precision. P C Dikshit Textbook of Forensic Medicine and Toxicology, “Determination of Intrauterine Age.”
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