HomeGynaecology CareFetal Ultrasound - Procedure, Why is it Needed, Types and Risks

Fetal Ultrasound – Procedure, Why is it Needed, Types and Risks

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When a woman is pregnant and visits a doctor for a checkup, ultrasound examinations are very much a part of the screening. This technique is medically termed fetal ultrasound, as ultrasonic sound waves are used to get an image of the fetus growing in the mother’s womb. This image helps the doctor detect if there is anything wrong with the baby or if he/she is growing well . The sonogram of the fetus also confirms his/her age or the duration of the pregnancy, which helps the doctor assess when the baby will be born.

How is the procedure done?

There is an electronic wand called a transducer, from which ultrasonic sound waves are emitted and reach the patient’s body. This transducer is slowly moved up and down the abdomen of a pregnant woman. Sound waves pass through her skin, muscles and blood to the fetus in her uterus. Then these sound waves are reflected by the baby’s body and come back to the transducer. These returned sound waves are converted by the transducer into electronic images, which can be seen on a computer screen.

Why is fetal ultrasound needed? 

The fetal ultrasound is conducted during the first trimester to confirm the pregnancy and how many fetuses are there in the mother’s womb. It also confirms the gestational period of a woman or in simpler words, for how long she has been pregnant. This test is also necessary for checking if there is any defect in the uterus or cervix of the woman that may cause a problem for the health of the fetus and the mother.

Another fetal ultrasound test is essential during the second trimester, preferably between the 18th and 20th week of pregnancy. At this stage, the ultrasound can check the health condition and the growth of the baby more precisely. It can also detect if there is any inborn defect in the brain, limbs or an internal organ of the growing fetus.

The doctor may conduct an ultrasound just before the delivery, to ascertain whether the position of the baby is right for normal delivery. You may consult your healthcare provider or doctor for if you feel anything wrong during your pregnancy. In case of sudden vaginal bleeding, the doctor may recommend an ultrasound for checking the status of the pregnancy 

Different types of fetal ultrasound tests

  • Transabdominal ultrasound – The transducer is moved over the lower abdomen of the pregnant woman to get the images of the fetus in her womb. This is the standard method, producing only 2D pictures on the attached computer screen.
  • Transvaginal ultrasound – The transducer is passed inside the vagina of the pregnant woman so that sound waves can travel up to her uterus and gather images of her growing baby. This test is conducted only during the first trimester to confirm pregnancy.
  • Doppler ultrasound – This ultrasound records even the tiniest changes when the sound waves collide with blood particles. Thus, it is used for checking the blood flow in the baby’s body.
  • 3D ultrasound – Instead of the usual 2D images, this test shows a 3D image of the fetus on the attached computer screen. Several 2D images are joined together to form a 3D image. Thus, it helps doctors to study physical abnormalities of the baby and any defect of the neural tube.
  • 4D ultrasound – This test shows the movements of the baby in the mother’s womb, with the help of several 3D pictures. 
  • Echocardiography of fetus – This test is done to study the condition of the heart of the unborn baby. It is a useful step in detecting congenital heart problems in the fetus.

Your healthcare provider may use fetal ultrasound to:

  1. Confirm pregnancy and its location. Some fetuses may develop in the fallopian tube, outside of the uterus. A fetal ultrasound can help the health care provider detect ectopic pregnancy – a pregnancy outside of the uterus.
  2. Confirm the number of babies in the womb. If your healthcare provider is suspecting  multiple pregnancy, he/she may recommend an ultrasound to confirm the number of babies.
  3. Determine the gestational age of your baby. Knowing the age of your baby can help the healthcare provider to determine your due date and track various other milestones throughout the pregnancy.
  4. Study the levels of placenta and amniotic fluid. The placenta provides the baby in your womb with oxygen-rich blood and vital nutrients. The fluid that surrounds your baby in the uterus during pregnancy is called amniotic fluid. Too much or too little of amniotic fluid or complications with placenta need special attention. Therefore an ultrasound is recommended to help determine amniotic fluid and the placenta around your baby.
  5. Evaluate the growth of your baby. Your healthcare provider might use ultrasound to determine whether your baby is growing at a normal rate. Ultrasound can be used to monitor the movement of your baby including breathing and heart rate.
  6. Identify birth defects. An ultrasound may help your healthcare provider screen for any birth defects.
  7. Investigate complications. If you are bleeding or are experiencing other complications, an ultrasound may help your healthcare provider understand the cause.
  8. Perform other prenatal tests. Your healthcare provider may use ultrasound to guide needle placement during some prenatal tests like amniocentesis or chorionic villus sampling.
  9. Determine fetal position before your delivery. Many babies are positioned head-first by the end of your third trimester. However, this does not happen always. Ultrasound imaging will help confirm the baby’s presentation so that your doctor can discuss options for delivery.

Risk factors associated with fetal ultrasound

Ultrasound technique is much safer than X-ray, as sound waves do not cause any harm to the pregnant woman or her unborn baby. The movement of the transducer over the abdomen or through the vagina can be a bit uncomfortable for some women.  The transducer has a latex covering, which may cause discomfort to those suffering from latex allergy. Moreover, certain defects may not be detected through the fetal ultrasound method.

Preparation for the fetal ultrasound test

Women who need an abdominal ultrasound during their pregnancy are asked to come with with a full bladder to the ultrasound department. This helps in: 

  • Visualising the woman’s uterus easier by pushing any loops of her bowel up and out of the way, particularly during her early pregnancy. The bowel contains gas (or air) and ultrasound waves cannot travel well through air.
  • Moving the uterus higher up in the woman’s belly, making it easier to see the unborn baby.
  • Making the bladder clearer to identify on ultrasound, particularly during her later pregnancy. But, a partially full bladder is generally sufficient for an ultrasound examination during the later pregnancy.

What to expect from fetal ultrasound

You will need to lie down on an examination table. The attending technician will apply a gel all over your abdomen for conducting a transabdominal ultrasound. Then the transducer will be moved up and down the abdominal region to get anatomical images of your baby. For a transvaginal ultrasound, the transducer is covered with a plastic sheet and water-based gel before inserting inside the vagina while you rest your feet within the stirrups beside the examination table. This gel can be wiped off the abdomen or vagina after the ultrasound is done.


Since fetal ultrasound is done with the help of advanced technology, you should get this test done at a reputed medical institute

Frequently Asked Questions (FAQs)

When is the first fetal ultrasound needed?

You need the first ultrasound between the 6th and 9th week of your pregnancy. The aim of this test is mainly to confirm your pregnancy and its location .

Can fetal ultrasound have any negative effect on the baby?

Unlike X-ray radiation, the sound waves for fetal ultrasound tests are absolutely harmless for your baby.

When will the result of fetal ultrasound be available?

Ultrasound images can be seen and evaluated by a healthcare provider as and when they appear on the computer screen. But, the printed images and the result in written formats may be given only after some days. 

Is the fetal ultrasound test painful? 

You will not experience any pain.

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