A 9-week fetus, for example, would have a CRL of 2.5 cm (Fig. CRL has been promoted as the most accurate method of dating a pregnancy, but experience has shown that the average of the biparietal diameter (BPD), femur length, and abdominal circumference obtained before 20 weeks' gestation is comparable in accuracy.
The measurement is determined, by convention, from the outer edge of the proximal fetal parietal bone to the inner edge of the distal parietal bone (Fig. The gestational age is estimated by comparing the observed BPD to tables relating BPD to gestational age.
Both clinical and ultrasonographic gestational age are expressed using this standard.
The use of endovaginal ultrasound has greatly enhanced our ability to detect pregnancy early.
This image of the fetal cranium perpendicular to the midline in the occipitofrontal plane typically is used for measurement of the biparietal diameter (BPD).
The BPD is measured from the outside of the proximal skull table to the inside of the distal skull table.
The crown-rump length (CRL) of the fetus is an accurate predictor of gestational age.