The 18-20 week scan is like a clinical examination of the fetus. In some situations , the scan may be postponed up to 22 weeks During this scan, the head, face, heart, lungs, stomach, bladder, kidneys and limbs of the fetus are thoroughly scanned. Fetal activity is also observed during scanning. The umbilical cord, location of the placenta, which gives nutrition to the baby and the amniotic fluid that surrounds the fetus are examined. The length of the cervix of the uterus is measured
In some instances, a “Doppler Study” is performed to evaluate the blood flow to various parts of the baby especially the placenta and the brain. Blood flow to other organs may be studied in indicated cases
It is important to remember that majority of babies are normal. Birth defects are seen only in 1- 2% of pregnancies. In some cases, there may be some minor variations observed during the scan. This should not cause anxiety and the expert can help to understand these findings better. Some abnormalities though may not be picked up on ultrasound
1. How long does it take to complete the first trimester scan or the second trimester scan ?
ANS: The average time taken for the scan is expected to be around 20-30 minutes. Sometimes the mother may be asked to walk around after the initial scan so that the fetus may move to a more conducive position suitable for scanning . The mother may also be asked to turn to the left or right for better visibility.
However, The time taken for each scan depends on various factors. Some of the factors which are expected to prolong the scan time are
a. Bodily habitus of the mother (high BMI)
b. Fetal position and activity
c. Amount of fluid around the baby
d. Findings on scan which look unusual
e. Multiple pregnancy
f. Organs not routinely imaged ( ear, fingers and digits etc)
g. The type of equipment used
2. Can all the anomalies be detected after a first and second trimester scan?
ANS: While all attempts are made to scan the fetus in detail, various factors listed above may limit the examination an the capability to complete the scan in full. Moreover, the ultrasound scan is meant for identifying large severe defects and not minor abnormalities. Hence abnormalities of the ear or the toes and digits may go unnoticed.
