Growth Scan & Doppler Flow Studies
The Growth scan & Doppler flow ultrasound is usually performed between 28 weeks and 32 weeks of your pregnancy. The purpose of the ultrasound is to:
– Provide information about your baby’s size and how well your baby is growing (growth velocity).
– Describe the position of the placenta. If your placenta is low on the 20 weeks, there is a good chance that it has moved up out of the way of the cervix at this time of pregnancy. In some cases however, the placenta is still near or over the cervix.
– It is not very accurate to estimate your due date of pregnancy at this gestation but this can be used as basis only of there were no previous ultrasounds done and the mom does not know or unsure of her last period.
– Doppler flow scan is done to check the blood flow in different parts of your baby’s body such as his umbilical cord. This helps to show whether or not the baby is getting all the oxygen and nutrients he needs via the placenta.
What happens during a fetal growth scan?
During the fetal growth scan, various measurements are taken by the doctor. The main fetal measuremens includes:
Biparietal Diameter (BPD) – measures across the head
Head Circumference (HC) – measures around the head
Abdominal Circumference (AC) – measures around the abdomen
Femur Length (FL) – measures the length of the thigh bone
An estimate of fetal weight (EFW) can be calculated by combining the above measurements. The EFW can be plotted on a graph to help determine whether the fetus is average, larger or smaller in size for its gestational age. If the fetal weight estimate is below the bottom 10 percent line on the graph, it is considered to be small for gestational age (SGA). If the fetal weight is above the top 10 percent line on the graph, it is considered to be large for gestational age (LGA).
It is important to note that repeated ultrasound measurements of the same fetus can vary and the estimated fetal weight may be incorrect by as much as 20 percent.
A fetal growth scan does not routinely check the baby for abnormities. An ultrasound scan to look for major fetal abnormalities is routinely performed earlier in pregnancy between 18 and 20 weeks gestation (see the morphology scan).