Third Trimester Scan

Some examples of reasons to have a third trimester scan are:

• The foetus, or the mother’s abdomen, feels too big or small for the stage of pregnancy.
• The mother has a medical condition that can affect fetal growth and well-being, such as high blood pressure or gestational diabetes.
• The placenta was low-lying on the midtrimester ultrasound.
• The position of the fetus could be unusual e.g. breech.
• Abnormal symptoms such as pain or bleeding.
• Movements decrease.
• A fetal abnormality was noted at an earlier ultrasound and requires a follow-up.

• Fetal position.
• Fetal size: an estimated fetal weight is calculated from measuring the fetal head, abdomen and femur. 
• The weight ‘estimate’ is truly that, with one standard deviation being 15% either side of the true weight.
• Some assessment of fetal anatomy: bearing in mind, late pregnancy limits the views and the check will not generally be a universal check, like the 19-week ultrasound.
• Placental position and maturity.
• Amniotic fluid volume.
• The Doppler blood flow in the umbilical cord and the brain. This gives an idea of the placental function and reserve.
• Fetal movements.
• Other factors that are requested by the referring doctor.