Regarding IUGR
‘AC is the single most sensitive parameter to detect IUGR’
Dutta Obs 7/e, p 462
‘Serial measurements of AC (not BPD) and estimation of fetal weight are more diagnostic to fetal growth restriction’
Dutta Obs 7/e, p 462
Head circumference (HC) and abdominal circumference (AC) ratios: In a normally growing fetus the HC/AC ratio exceeds 1.0 before 32 weeks. It is approximately 1.0 at 32 to 34 weeks. After 34 weeks, it falls below 1.0. If the fetus is affected by asymmetric IUGR, the HC remains larger. The HC/AC is then elevated. In symmetric IUGR, both the HC and AC are reduced. The HC/AC ratio remains normal. Using HC/AC ratio, 85% of IUGR fetuses are detected
Pathophysiology: Basic pathology in small for gestational age is due to reduced availability of nutrients in the mother or its reduced transfer by the placenta to the fetus. It may also be due to reduced ultilization by the fetus. Brain cell size (asymmetric–SGA) as well as cell numbers (symmetric-SGA) are reduced. Liver glycogen content is reduced. AC indirectly reflects the decreased fetal liver size and glycogen content.
Abdominal circumference (AC) is the least sensitive parameter for detection of IUGR
In asymmetric IUGR head circumference/abdominal circumference (HC/AC) is reduced
Serial biparietal diameter (BPD) is the only important measurement in IUGR
AC indirectly reflects fetal liver size and glycogen storage