This is usually done at 30 to 37 weeks. The following details are assessed at this scan:
a) Measurements of head circumference, abdominal circumference and femur length to
check if the biometric measurements of the fetus are appropriate for the gestational
age of the fetus.
b) Detection of some late onset structural abnormalities (1:200 abnormalities are
detected after a normal first and second trimester scan).
c) Doppler studies of the uterine, middle cerebral and umbilical arteries. Calculation of
the cerebroplacental ratio (this is an assessment of the placental reserve) from 36 weeks onwards may be useful in timing the delivery of the fetus. Measurement of the uterine artery Doppler on the recently implemented module on the Astraia program that the clinic uses allows the risk assessment for pre-eclampsia before 36 weeks and at term. An optional blood test to check for Placental growth factor (PlGF) may further increase the detection rate of pre-eclampsia.
d) 3D and 4D scans - These are only possible when the fetus is facing the front of the
abdomen and there is adequate amniotic fluid in front without obstruction from the limbs or umbilical cord. This may promote bonding with the parents.