The second trimester target scan is the gold standard fetal evaluation scan:
- assessment of fetal support system;
- assessment of fetal activity and behaviour;
- assessment of fetal size;
- assessment of fetal structure, the anomaly scan, and
- assessment of cervical support to know the risk of premature delivery.
Fetal support system consists of the placenta, umbilical cord, and the amniotic fluid. Abnormalities in the appearance of the placenta or umbilical cord (such as single umbilical artery) may indicate the need for close follow up to see if the fetal growth is at par with the expected standards.
Fetal activity and behaviour forms an important part of the examination, since by the time of the 20-week scan there is a predictable pattern of movements in all fetuses. For example, rolling/flipping over; bending and extending the limbs; opening and closing of the hands; yawning/swallowing; breathing/hiccups; reaching out to the face etc. Normal pattern of fetal activity reassures normal brain function to a large extent.
Fetal structural assessment involves a systematic documentation of the different organs of the fetal body, both external organs, and internal organs. In the absence of any abnormality in these standard views, the chance of malformation of any of the organs is very low.
Cervical support is assessed usually by a transvaginal (internal) scan. The cervix is the neck of the womb and has an important role in maintaining the pregnancy until full term. By meticulous examination of the cervix, its appearance, and its length we will be able to predict the chance of a preterm birth or cervical insufficiency to a large extent. Appropriate treatment will be discussed with your primary physician. The target scan is usually performed between 18 and 22 weeks.