Biparietal Diameter
    assessed at the level of the thalamus and 3rd ventricle with measurements from outer to inner wall, or from mid to mid wall.
    accurate to +/- 1 wk in 1st and 2nd trimester, +/- 2wks thereafter with shape changes due to multiple gestations, ruptured membranes and term dropping precipitously
    BPD is an accurate predictor if no dolichocephaly/brachycephaly (assessed with Cephalic Index = BPD/fronto-occipital diameterx100 between 75-80)

Head Circumference
    assessed at BPD level, with added criteria of cavum and tentorial hiatus in plane
    is more accurate than BPD, because it is shape independant
    measured at cranium excluding soft tissues
    ROT growth is 10mm per week

Abdominal Circumference (pic2)
     transaxial plane at the level of the umbilical/right-left portal vein junction including symmetric bilateral ribs including the subcutaneous soft tissues. Usually see through the fluid filled stomach
    ROT growth is 10mm per week

Femur Length
    measured at ends of blone, not including epiphysis. Most accurate when measured perpendicular to U/S beam
    bowing seen in osteogenesis imperfecta, dwarfism, hypophosphatemias
    fractures preclude use for age
    proximal femoral epiphysis is visible at 38wks GA (other Ossification Times)

Estimated Fetal Weight (EFW)
    using Hadlock charts and BPD+AC or AC+FL commonly

Intrauterine Growth Retardation (IUGR)
    occurs in 5% of low risk population
    discriminate constitutionally small from pathologically small by:
       -estimate GA (U/S, LMP), if:
            AC < 10th percentile suggests IUGR
            EFW < 10th percentile suggests IUGR
            FL:AC ratio > 23.5 suggests IUGR
       -umbilical artery Doppler S/D ratio > 4 suggests IUGR. High resistance pattern sensitive for severe fetal distress, whereas normal Doppler in small GA fetus usually have normal outcome
       -low amniotic fluid index <5 is found in severe IUGR;

    IUGR with polyhydramnios associated with high risk of chromosome abnormality (40%) and 60% mortality

    Symmetric IUGR: [fetal factors] 1st trimester insult, CHD, infection, with maintained small for dates throughout pregnancy HC/AC 1/2 at 16wks, and 1.0 at 36wks
    Asymmetric IUGR: [maternal factors] HTN, DM, smoking, cocaine, poor nutrition, placental abruption/insufficiency/infarction
    IUGR fetus is routinely followed weekly with routine exam and biophysical profile

Macrosomia
    large for GA with EFW >90th percentile or greater than 4000g
    NB only 2% of macrosomia is from diabetic mothers
    Symmetric: prolonged pregnancy or genetic factors
    Asymmetric: diabetes. Detect early as ++AC growth potential in 39th &40th wks


   

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