single most sensitive marker of intrauterine growth restriction in USG is :

USG is extremely useful not only to diagnose the growth retardation but also to identify a fetus of symmetrical or asymmetrical one. Sonographic predictive values that are commonly used are: * Head circumference (HC) and abdominal circumference (AC) ratios: In a normally growing fetus the HC/AC ratio > 1.0 before 32 weeks,= 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. Transcerebellar diameter correlates well with the gestational age. AC is the single most sensitive parameter to detect IUGR. * Femur length (FL) is not affected in asymmetric IUGR. The FL/AC ratio is 22 at all gestational ages from 21 weeks to term. FL/AC ratio greater than 23.5 suggests IUGR. * Amniotic fluid volume--The reduced amniotic fluid volume is often associated with asymmetrical IUGR. A veical pocket of amniotic fluid < 1 cm suggests IUGR. An AFI between 5 and 25 cm is normal and an AFI less than 5 indicates oligohydramnios. * Anatomical survey: To exclude fetal anomalies by sonography Reference: Dutta,s Textbook of Obstetrics 7th edition page no 463.