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The medical ultrasound is a diagnostic imaging technique that uses ultrasonic vibrations to create an image of the internal body. It can capture images of the internal body structures like the muscles, tendons, blood vessels, joints, and other organs. It helps to find the source of a disease or even find out the position of certain abnormalities.


However, the foetal ultrasound is a very common prenatal test and is offered to every pregnant woman. Sound waves show a picture of the baby in the uterus. Ultrasound helps the health provider to check if the baby is healthy and developing properly. The ultrasound is also a special part of the pregnancy, allowing you to see your baby for the first time. You would be able to see the hands, legs and other parts of the baby depending on the time of the ultrasonography.

What are the two types of ultrasonography?

There are mainly two types of ultrasonography:

  • Transabdominal ultrasound - It is performed by moving the transducer over the abdomen.
  • Transvaginal ultrasound - A transducer is placed in the vagina to send sound waves and gather the reflections. The transvaginal ultrasounds are used during early pregnancies. It might even be done if the transabdominal ultrasound does not offer the required information.

There are other types of transabdominal ultrasounds as well:

  • Specialized sonographic evaluation - This examination is used when a foetal abnormality is suspected. A more detailed evaluation would offer additional information about the abnormality.
  • 3D Ultrasound - The exam would offer a two-dimensional display of the 3D data. It would help to detect neural tube defects or facial abnormalities.
  • Foetal echocardiography - The exam would offer a detailed picture of the heart of the baby. A congenital heart defect can be used to confirm with its help.
  • Doppler ultrasound - Very slight changes in the ultrasound waves can be measured through this kind of ultrasound when they bounce off moving objects, like the blood cells. It can offer details about the blood flow of the baby.

Why is an ultrasound performed?

The first-trimester ultrasound is performed to find the presence, location, and size of the embryo. It determines the number of foetuses and estimates how long the tenure of pregnant. The ultrasound can be used for screening of abnormalities in the cervix and uterus.

The standard ultrasound performed in the second or third trimesters would evaluate several features of the pregnancy, including the anatomy of the fetus. The timing of the ultrasound might vary from 18 to 20 weeks of pregnancy.

The healthcare might use the foetal ultrasound for the following reasons:

  • Confirming the pregnancy and its location - Often foetuses develop outside the uterus, in the fallopian tube. A foetal ultrasound could help your health care provider detect if the pregnancy is outside the foetus.
  • Determine the gestational age of the foetus - Knowing the age of the baby could help determine the due date and other milestones of the pregnancy.
  • Finding the number of foetuses - The ultrasound would confirm if there are multiple pregnancies.
  • Evaluating the growth of the baby - The healthcare provider could evaluate if the baby is growing at a normal rate.
  • Identify birth defects - The healthcare provider could find out if there are birth defects.

You might be asked to drink a certain amount of fluid or avoiding depending on the type of ultrasound being performed. You should ask the healthcare provider for further instructions.

Authored by Dr. Radhika Meka

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