Which statement about obstetric dating and assessment is correct
Deferring the study for a short time may allow the fetus to assume a more favorable position.If an appropriate BPD cannot be obtained, an alternative fetal dimension is chosen.Using a vaginal probe, the gestational sac and fetal pole can be found earlier than with the abdominal approach.The endovaginal transducer eliminates the need for a full bladder before examination and significantly improves resolution in obese patients.The earliest ultrasonic evidence of pregnancy is the finding of a fluid-filled gestational sac with an echogenic border.A gestational sac should be visible at 4 weeks and 4 days, a yolk sac at 5 weeks, and a fetal pole with cardiac activity at 6 weeks.The BPD is the largest transverse measurement of the fetal skull and usually is measured from an occipitofrontal scan plane at the level of the fetal thalami and the septum pellucidum cavum (Fig. The fetal head should have an oval shape with clear midline margination.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.
From 14 weeks onward, the BPD is one of several useful estimators of fetal gestational age.
The role of ultrasonography in obstetric practice has continuously evolved since its introduction more than 40 years ago.
Indeed, it is difficult to imagine a modern obstetric practice without access to the information provided by real-time ultrasound.
The occipitofrontal diameter is measured in the same plane as the BPD and is a measurement of the longitudinal axis, by convention taken from outer skull tables on each side.
This measurement can be averaged with the outer-to-outer skull measurement in the transverse plane to provide a basis for estimating head circumference.
Measurement of the fetal limb bones also may be used to determine gestational age.