It allows the practitioner to view the baby inside the mother’s uterus (womb). It is useful in providing information about the health of the baby and the progression of the pregnancy.
Ultrasound is a safe procedure to perform during pregnancy as long as there is the minimal exposure for the baby. It should only be performed by specialists to reduce the time of exposure. The only downside is the Doppler which is preferably not used during the first 3 months of pregnancy.
There are 2 types of ultrasound used during pregnancy: the transvaginal and the transabdominal.
The transvaginal is used in the first trimester while the latter is used the the second and third trimesters.
Three routine ultrasound examinations are usually performed during a normal pregnancy.
The first trimester ultrasound is preformed between 11 and 14 weeks of pregnancy. This goal of this examination is to estimate the gestational age (the age of the baby) by measuring the CRL (the length of the fetus from head to bottom). This measurement is the most accurate during a pregnancy. It also serves to measure the NT (the neck thickness) and the nasal bone. These measurements give us an idea about the risk of chromosomal abnormalities (trisomy) in the fetus.
The second trimester ultrasound is performed between 20 and 24 weeks of pregnancy. Because of its huge importance, in some countries it is the only ultrasound that is performed during pregnancy. This is called the morphology scan, or the fetal anomaly scan. It is performed in order to look for any abnormalities in the baby’s structural development and growth, such as spina bifida or heart anomalies, and to check the position of the placenta. The sonographer will check that there is only one baby, and confirm the due date. He/she will show the patient the heartbeat and parts of the baby like the face and hands. it also reviles the sex of the baby. The scan takes about 15-20 minutes.
The third trimester scan is performed between 31 and 35 weeks. It is mostly a growth scan and it assess the fetal well being, placental location fetal presentation (head or breech), and measurement of the cervical length; As well as follow up on any abnormalities seen in the anomaly scan.
Finally, it is important to mention that the examination results depends on multiple factors such as the fetal lie, the mothers weight and fat composition, the expertise of the sonographer and the machine he is using. Moreover, ultrasound can only reveal 60% of the abnormalities of the baby, and this information should be provided to all patients undergoing the examination.
by Dr. Joe Feghali