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Femur Length to Abdominal Circumference Ratio

Description

The ratio of the femur length to abdominal circumference is constant in the normally growing fetus from 21 weeks of gestation to term, being independent of menstrual age. An increase in the ratio above normal can be seen in fetuses who are small for gestational age.


 

femur length to abdominal circumference ratio =

= (femur length in cm) / (abdominal circumference) * 100

 

Interpretation:

• infants who are small for gestational age have a ratio >= 23.5; however, due to the low prevalence of growth retardation in a general population, only 25% of infants with a ratio >= 23.5 will be growth retarded

• infants who show appropriate development for gestational age have a ratio < 23.5, with values around 22

• large for gestational age infants have a ratio around 21

• once an infant has been identified as being at risk for growth retardation by the femur length to abdominal circumference ratio, then other criteria for growth should be monitored rather than the ratio, as the ratio can return to normal in infants who are growth retarded

 


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Specialty

ICD-10