An ultrasound (also called a Sonogram or Scan) is a routine diagnostic test that is usually prescribed during the first and second trimester of your pregnancy. It is usually done to confirm that the placenta is healthy and attached normally and that the baby is growing properly in the uterus.

Ultrasounds are also valuable, as they can also show up major anatomical abnormalities or birth defects in the growing fetus. In a prenatal ultrasound, the echoes are recorded and transformed into video or photographic images of your baby – for future reference.

How It Works

Medical ultrasounds work much on the same principle as sonar (used in oceanography to map the sea bed). During an ultrasound, high-frequency sound waves which are inaudible to the human ear are sent through your tummy into the uterus. These bounce off the baby as echoes and get translated into an image by the computer.

The images of the baby you see show the movements and position of the baby along with other vital parts like the amniotic sac, placenta and ovaries.

When Is An Ultrasound Performed And Why?

During pregnancy, an ultrasound is generally performed at around 20 weeks gestation. That’s when you can hear the baby’s heartbeat and catch a glimpse of its body movements. You can also determine the gender of the baby around this time. However, as you would be aware, foetal sex determination through ultrasound is banned and a punishable offence in India.

Your practitioner may recommend ultrasound examinations more than once during the course of your pregnancy.

An Early Pregnancy Ultrasound is Usually Performed to Determine:

• Presence of more than one fetus
• Due date or gestational age (the age of the fetus)

Later in Pregnancy, an Ultrasound may be used to Determine:

• Health of the baby
• Location of the placenta
• Amount of amniotic fluid around the baby
• Position of the baby
• Baby’s expected weight

Types Of Ultrasound

There are many different types of ultrasound technology that can be used during pregnancy, for various reasons:

Abdominal Ultrasound

Also known as “trans-abdominal”, this is the most common method used, especially after 12 weeks of pregnancy (when the uterus has grown up and out of the woman’s bony pelvis).

Vaginal Ultrasound

The vaginal or “trans-vaginal” ultrasound is performed by placing a sterilized ultrasound probe inside the vagina. This method is often used during fertility treatment or early pregnancy (less than 12 weeks) as it enables the sonographer to look more closely at the woman’s uterus. Vaginal ultrasounds may also be more beneficial if the woman has a retroverted or ‘tipped’ uterus (up till 12 weeks of pregnancy) or if the sonographer needs to view the woman’s cervix or detect a low-lying placenta.

Doppler Ultrasound

‘Doppler ultrasounds’ are done in the same way as abdominal ultrasounds, but they study the movement of blood (usually through a blood vessel). They are used to assess the functioning of the placenta and the well-being of the baby.

3D & 4D Ultrasound

Though not widely used, ‘three-dimensional’ ultrasounds (also known as ‘ultrasound holographs’ are sometimes recommended to have a better look at an abnormality that may have been detected in a routine ultrasound.

3D ultrasounds work by taking thousands of image ‘slices’ in a series (called a ‘volume of echoes’). The volumes are then digitally stored and shaded to produce 3 dimensional images of the baby that look more life-like. 4D (or ‘four-dimensional’ images) just means the images can be seen to move in ‘real time’ so the activity of the baby can be studied.

Ultrasounds during pregnancy can be very useful and provide a lot of information, but it is important to remember that they also have their limitations. The accuracy of a pregnancy ultrasound will very much depend on the qualifications, skill and experience of the sonographer performing the examination, as well as the Doctor’s skill at interpreting the images.