Fetal growth is relatively constant, with little biological variability in early
pregnancy. As the pregnancy progresses there is more variability in the
measured versus true gestational age.
With the exception of crown-rump length, there is probably no other
morphometric variable that is more or less predictive of fetal age than any
other variable. The accuracy of fetal age determination is inversely related to
fetal age. The variables selected to estimate gestational age will depend on
the fetal age. The more variables used, the more accurate the age estimate will
be.
- BPD as a measure of IUGR.
- Sensitivity of 50-60%
- Positive predictive
value of less than 10% (1).
- In severe dysmature
IUGR with oligohydramnios, compression of the fetal head and
dolicocephaly may further affect the BPD.
- Femur length also has a low
predictive accuracy when used alone (2). In short limb dystrophies, which
are often associated with IUGR, the short long bones are the key to making
the diagnosis.
- Kurjak A, Kirkenin P, Latin
V. Biometric and dynamic ultrasound assessment of small for dates infants:
Report of 260 cases. Obstet Gynecol 1980;56:281.
- Woo J, Wan CW, Fang A et.al.
IS femur length a better predictor of fetal age in the growth retarded
fetus as compared with biparietal diameter? J Clin Ultrasound 1985;4:132.