<prompt> Regarding IUGRAbdominal circumference AC is the least sensitive parameter for detection of IUGRIn asymmetric IUGR head circumferenceabdominal circumference HCAC is reducedSerial biparietal diameter BPD is the only important measurement in IUGRAC indirectly reflects fetal liver size and glycogen storage  <response>: AC is the single most sensitive parameter to detect IUGRDutta Obs 7e, p 462Serial measurements of AC not BPD and estimation of fetal weight are more diagnostic to fetal growth restrictionDutta Obs 7e, p 462Head circumference HC and abdominal circumference AC ratios: In a normally growing fetus the HCAC 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 HCAC is then elevated. In symmetric IUGR, both the HC and AC are reduced. The HCAC ratio remains normal. Using HCAC ratio, 85 of IUGR fetuses are detectedPathophysiology: 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 asymmetricSGA 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. 