Ethnic considerations in ultrasonic scanning of fetal biparietal diameters.

Biparietal diameters (BPD) were determined by ultrasonography on 86 Caucasians and 107 Polynesians at different gestations. Analysis of variance showed a highly significant (p less than 0.01) difference between groups. At any gestational age, Polynesian fetuses had BPDs 1.89 mm greater than Caucasian fetuses and this fact must be taken into consideration when a single measured value of BPD is being used in the estimation of gestational age. In areas where the obstetrical population comprises different ethnic groups, there is a need for establishing local reference tables by race.