It is common to make at least 2 and often 4 or 5 measurements to estimate gestational age.In most cases, BPD [Biparietal diameter], HC [Head circumference], AC [Abdominal circumference] and FL [Femur length] are used.
These measurements are more appropriately used in the assessment of fetal growth, particularly in the second half of the pregnancy, than in the assessment of gestational age.
It is, however, an appropriate measurement in the second trimester to demonstrate normal fetal proportions.
BPD - OFD - HC | Femur and Humerus (FL HL) | Abdominal Circumference (AC) Fetal Weight Percentile Charts | Fetal Growth Percentile Charts Measurement Standards | Ultrasound Measurement Chart | Crown-Rump Length After the first trimester of pregnancy a multiparameter assessment of gestational age is advocated.
This should include at least two fetal measurements (usually biparietal diameter (BPD) and femur length (FL)) plus a consideration of additional parameters such as head circumference (HC), occipitofrontal diameter (OFD), abdominal circumference (AC) and humerus length (HL).
Doing an ultrasound to estimate fetal weight near term is a very common practice, one still employed by many OBs, especially with large mothers.
However, research clearly shows that this is a very questionable practice.The original definition of a crown-rump length (CRL) was by Mall in 1907.The CRL is the sitting height, midbrain to the lowest point of breech.This is preferable to just averaging all values to arrive at an estimated gestational age.The wide normal range of BPD in late pregnancy must be appreciated.Measurements in the beam axis are more accurate than those made across the axis. Crown-Rump Length (CRL) and femur length) should be measured across the axis.