The growth scan is typically done in the third trimester of pregnancy, i.e after the 28th week. The main objective of this scan is to assess the fetal size and the speed of growth (growth velocity). The scan is typically advised at 34 weeks if there are no other risk factors in the pregnancy. However, if there are any risk factors, then the monitoring usually starts at 28 weeks.
Factors that are significant to impact fetal growth include:
- Maternal diseases (heart, lungs, connective tissue disorders etc),
- A poor outcome in previous pregnancy (high blood pressure, low birth weight baby, or both),
- Abnormal blood test report in the first trimester screening or quadruple screening,
- An abnormally looking placenta in the fifth month scan, or
- The height of the uterus not corresponding to the stage of pregnancy.
While assessing for the fetal well-being, we look for fetal nutritional status and oxygen status. A well fed fetus is likely to be of appropriate weight for the stage of pregnancy and will show the correct speed of growth. The oxygen status is deduced from a combination of findings including how well the mother perceives the fetal movements, the pattern of movements observed during the scan, the fluid level around the fetus, and finally, the blood flow in the fetal brain. In addition to testing the fetal well-being, this scan is also utilised to correctly identify if the fetal head is in correct position and if the placenta is away from the neck of the womb. Fetal head position can also be easily assessed by clinical examination. Finally, we check four organs for evolving / late manifesting defects: the brain, heart, intestines, and kidneys.