<prompt> single most sensitive marker of intrauterine growth restriction in USG is :ACAFIFLBPD  <response>: 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 HCAC 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 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 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 FLAC ratio is 22 at all gestational ages from 21 weeks to term. FLAC 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. 