Fetal Age Estimation Using Biparietal Diameter

Interpretation of Fetal Biometry Measurements

The American College of Obstetricians and Gynecologists recommends using the biparietal diameter to estimate gestational age, with a measurement of 8.5 cm corresponding to approximately 32-33 weeks of gestational age in a normally developing fetus, although the precision of this measurement decreases significantly in the third trimester 1

The American Journal of Obstetrics and Gynecology suggests that a discordant biparietal diameter measurement with expected gestational age based on dating criteria should prompt evaluation for skeletal dysplasia, fetal growth restriction, or macrosomia, using the femur length to biparietal diameter ratio as a key predictor, particularly at 18-20 weeks gestation 1, 2

The American College of Radiology recommends regular assessment of fetal growth through ultrasound, following standard obstetric protocols, including fetal biometry assessment with measurements such as fetal biparietal diameter/head circumference, abdominal diameter/abdominal circumference, and fetal femur length 3
Standard prenatal care is sufficient for monitoring maternal health, with the American College of Radiology suggesting that regular assessment of fetal growth through ultrasound is recommended, following standard obstetric protocols 3

The American College of Obstetricians and Gynecologists recommends using the BPD-to-nasal bone ratio to assess for hypoplastic nasal bone, a soft marker for aneuploidy, with a ratio defined as BPD-to-nasal bone of 10 or 11 4
The American Journal of Obstetrics and Gynecology suggests that BPD must be measured perpendicular to the longitudinal axis in the appropriate plane to ensure accuracy 4