Ultrasonic diagnosis of the large-for-dates infant.

Data on consecutive measurement of fetal biparietal diameter (BPD) and fetal chest area in 42 normal weight infants (birthweight 10--90th percentile) and 30 large-for-dates (birthweight above the 90th percentile) are presented. Pregnancy duration varied from 32 to 40 weeks. In the normal weight group fetal BPD and chest area were above the 95th percentile fo the normal curve in 7% and 5% of the cases; in the large-for-dates group the figures were 7% and 47%. Head to chest ratio fell below the fifth percentile of the normal curve in 53% of the large-for-dates against only 2% of the normal weight infants. In the detection of the large-for-dates infant ultrasonic measurement of fetal chest area appears to be superior to ultrasonic measurement of fetal BPD.