Ultrasonic assessment of fetal head and body sizes in relation to normal and retarded fetal growth.

Data on consecutive ultrasonic measurements of fetal biparietal diameter (B.P.D.) and fetal chest area in 303 normal and 84 small-for-dates fetuses are presented. Duration of pregnancy varied from 24 to 41 weeks. A normal curve of the fetal B.P.D., chest area, and head-to-chest ratio was constructed. At 24 weeks mean fetal B.P.D. was 6.29 cm., mean fetal chest area was 24.9 sq. cm., and mean head-to-chest ratio was 1.59. At 41 weeks the mean values were 9.81 cm., 92.4 sq. cm., and 1.05, respectively. In the group of small-for-dates fetuses, a normal head-to-chest ratio was almost always associated with early onset of fetal growth retardation whereas in the majority of fetuses with increased head-to-chest ratios, growth retardation appeared to have started only in the third trimester of pregnancy.