Prenatal ultrasonographic fetal iliac bone measurement. Correlation with gestational age.

The variety of circumstances under which ultrasound examinations are performed makes fetal iliac bone measurement an important indicator of gestational age. We studied 322 well-dated pregnancies from 13 to 40 weeks' gestation with sonogram measurements of the fetal iliac bone in order to examine the relationship between gestational age and bone length. The results indicate a linear relationship, as described by the equation iliac length = -0.376 + (0.0887) (gestational age). The fit of the data to a straight line was quite close (R2 = .877, P = .0001). The data were used to obtain a nomogram for growth of the fetal iliac bone.