In cases of symmetrical growth retardation, the fetal BPD will fall below the 10th percentile.
Semi-quantitative methods of estimating AFV include the deepest pocket measurement and the amniotic fluid index (AFI).
The single deepest pocket of amniotic fluid is measured vertically.
Technique The patient is examined while reclining, with the abdomen exposed.
Particularly late in pregnancy, this may not be a comfortable position for the patient, who can experience symptoms from inferior vena cava compression by the heavy, gravid uterus.
The AC may be measured directly, or calculated from the AP and transverse abdominal measurements. Although the AC can be used to calculate gestational age, it is more useful in determining fetal weight.
Combined with the BPD, with or without the fetal femur length, reliable formulas can be used to predict fetal weight.
The BPD can be used to determine gestational age with a 95% confidence of 10 to 14 days.
If the gestational age is already known with precision (1st trimester ultrasound scan), then the BPD can be used to evaluate fetal growth.
If it is at least 2 cm deep, then true oligohydramnios is not considered present.
Some sonographers and clinicians find this definition too restrictive and will measure the largest pocket in two diameters.
This divergence of growth rates has two important clinical implications: Amniotic Fluid Volume Amniotic fluid may be increased (polyhydramnios) in the presence of some congenital anomalies, diabetes, and fetal hydrops.