Fetal Biometry: Clinical, Pathological, and Technical Considerations

Sonographic measurements of fetal ultrasound parameters are the basis for accurate determination of gestational age and detection of fetal growth abnormalities. Selection of the most useful single biometric parameter depends on the timing and purpose of measurement and is influenced by specific limitations. CRL (crown-rump length) is the best parameter for early dating of pregnancy. Biparietal diameter (BPD) maintains the closest correlation with gestational age in the second trimester. In cases of variation in the shape of the skull, head circumference is an effective alternative. Abdominal circumference is the most useful dimension to evaluate fetal growth, and femur length is the best parameter in the evaluation of skeletal dysplasia. Use of multiple predictors improves the accuracy of estimates. An individual approach to each pregnancy is recommended for fetal growth assessment. The various epidemiological factors involved in fetal growth should be considered and specific charts for different communities should be used when possible. The methods of fetal weight estimation with their limitations and potential errors are presented. Clinical application of fetal biometry in abnormal growth is discussed in cases of small- and large-for-gestational-age fetuses, chromosomal aberrations, and skeletal dysplasias. Target Audience: Obstetricians & Gynecologists, Family Physicians Learning Objectives: After completion of this article, the reader will be able to describe the usefulness of fetal biometry in gestational-age assessment and estimation of fetal weight, to delineate the application of fetal biometry in the evaluation of abnormal fetal growth, and to list the most accurate measurements for predicting gestational age.