Growth of the BPD

You have already seen how measurement of the fetus in the first trimester can be used to establish gestational age. In the second, and to a lesser extent in the third trimester, measurement of the BPD correlates well with fetal age.

There are established graphs plotting BPD growth. From about 12 to 24 weeks, these allow accurate assessment of gestational age.

After 24 weeks, the variation of normal fetal size contributes to diminishing accuracy of the measurement in predicting the age of the baby.