Fetal ultrasound

Fetal ultrasound is a prenatal ultrasound also known as Sonogram. It is an imaging technique which uses high- frequency sound waves, not audible to the human ear, that are transferred by the abdomen through a small device known as a transducer to see inside the abdomen. It is a safe way to examine the growth and development of the baby. As a result, it forms the images of the baby in the uterus. Ultrasound helps to show the images of the developing baby, ovaries, amniotic sac and placenta. It also detects for any birth abnormalities. Fetal ultrasound helps to understand the profile of the growing baby and assists in managing the pregnancy in cases of any genetic defects, if present. The family can plan accordingly whether to continue or terminate the pregnancy. This ultrasound is also used to know the exact gestational age of the unborn.

Fetal ultrasound is usually done during the first trimester and then again in the second trimester (18-20 weeks) usually when the amniotic images are properly visible. Ultrasound can be done frequently in order to keep monitoring the baby’s health.

There is another enhanced imaging technique known as Transvaginal ultrasound, which produces a more magnified image of the baby. In this procedure, the probe is inserted through the vagina. This ultrasound is done usually in the early period of pregnancy to look for any problem in the ovaries or uterus. It helps prevent the risk of early labor as the test can assess if there is any shortening of the cervix.


Why it’s done? What are the risks? How to prepare for the procedure? Expected results from the procedure:

Ultrasound is generally advised for all pregnant women at the 12th week (Nuchal Scan), 18th week (Early anomaly scan), 24th week (late anomaly scan) and 30th week (Biophysical profile scan). However, it can be done at any time during the pregnancy. Some of the reasons for conducting the fetal ultrasound are as follows:

  • To know the exact gestational age. By conducting the ultrasound, the doctor can know the due date of the baby and can also find out several milestones through the pregnancy.
  • Confirm the pregnancy and its location. Fetal ultrasound can detect the location of the baby as some of the fetuses start evolving in the fallopian tubes instead of the uterus. It helps to find out an ectopic pregnancy (tubal).
  • Detect birth disorders. Through an ultrasound, the woman can be made aware of any birth defects or chromosomal disorders if any.
  • Confirms the number of babies. It can assist to find out multiple pregnancies and hence, confirm the number of babies.
  • Study placenta. The placenta plays an important role in supplying oxygen-rich blood and vital nutrients to the fetus. Ultrasound helps to study the proper position of the placenta and the amniotic fluid, which surround the baby.
  • Assessing the development of the fetus. It helps to record whether the growth of the fetus is normal or not. Ultrasound assists to record the heart rate, breathing, and movement of the baby.
  • To determine the baby's position. It helps to rule out if the baby is in an abnormal position and hence, C-section might be required during the delivery.
  • Investigation of signs and symptoms. Ultrasound helps to find out any complications like bleeding, so that they can be treated properly.
  • Other prenatal tests. Ultrasound is needed to guide the needle while performing some other prenatal tests like Chorionic villus sampling or amniocentesis.
  • Weight of the baby. In the later phase of pregnancy, ultrasound might be used to assess the approximate baby’s weight.

Fetal ultrasound is not harmful at all, either for the pregnant woman or for the developing baby as the ultrasound does not use any radiations like in case of X-Rays. The procedure is performed by an expert gynecologist or a trained radiologist. Fetal ultrasound has some constraints that it cannot identify all the birth defects and also sometimes falsely indicates a birth defect when it is actually not present. In some rare cases, the patient might get a reaction from the latex covering the small transducer. However, it happens only if the woman has an allergy to latex. In such scenarios, the doctor must be informed well beforehand.

The healthcare provider will state all the specific instructions to be followed before the fetal ultrasound. The patient is usually advised to drink a lot of water/fluids, approximately 4-6 glasses, before the ultrasound starts and keep the bladder full. The patients is asked to avoid urination before the ultrasound as it helps the healthcare provider to see inside the uterus easily. Due to the full bladder, the women undergoing the procedure might feel some discomfort but she is allowed to urinate as soon as the ultrasound is complete.

The fetal ultrasound can be performed in the following two ways:

  • Through the vagina also known as Transvaginal– This procedure is usually performed in the early phase (1st-10 weeks) of the pregnancy; at this time the fallopian tubes and the uterus is close to the vagina as compared to the abdomen. A wand shaped transducer is inserted into the vagina to direct the sound waves out to get an image. This type of procedure is considered better as compared to the abdominal procedure as it provides a closer and enhanced image of the baby’s growth details.
  • Over the abdomen also known as Transabdominal – In the transabdominal procedure, the transducer is put over the abdominal surface to know the gestational age to understand the growth pattern of the developing baby. There is no pain or irritation felt during the procedure. In addition, it is completely safe and takes around 20 minutes to complete the procedure.

The type of the procedure chosen for the patient by the doctor would depend upon either the stage of the pregnancy the woman or on any other complications which a mother might face including bleeding from the vagina or any infections at the site, etc. If the woman is advised to go for a transabdominal procedure, then she is advised to wear loose fitted clothes so that the abdomen can be easily exposed.

There are some other types of transabdominal ultrasounds available, as mentioned below.

  • 3D and 4D ultrasound – A 3D ultrasound form a three-dimensional image of the fetus inside the womb and a 4D ultrasound displays a moving image of the baby. The image is as clear as a photograph and assists in identifying any birth defects, facial abnormalities or neural tube disorders in the fetus. The 3D and 4D ultrasound are more advanced as compared to fetal ultrasound.
  • Fetal Echocardiography – The procedure is generally used to detect any congenital heart problems and provide a clear image of the 4 chambers of the fetal heart. This is a good method to diagnose such problems at an early stage. Compromise in fetal circulation can lead to growth restriction in the babies & this is seen in women with pregnancy induced hypertension commonly.
  • Doppler ultrasound – This procedure is used to point any blood circulation issues in the fetus as it can detect slight bouncing-off moving bodies and can therefore measure very small deflections of the sound waves.

 During the procedure –

Transabdominal Procedure:
The woman is asked to lie down on her back on the examination table with the abdomen exposed. A special clear gel is then applied on the abdominal surface to remove any air between the transducer and the skin. The transducer is then rolled over the abdominal area of the woman in a back and forth motion. The sound waves sent through the transducer are reflected and captured, forming an image on the monitor. The sonographer can also show the movement of the baby inside the mother. In this type of procedure, the vital details of the baby can be easily measured and recorded including any birth defects, the head size, thighbone, gestational age, the finger, hand, growth evaluation, movements, etc.

Transvaginal Procedure:
In this procedure the woman is asked to change into a hospital gown or to take-off the lower clothes.  The mother is asked to lie down on the examination table with legs open. A lubricated vaginal transducer will be inserted into the vaginal canal. The image is formed on the monitor screen by the sound waves reflected through the bones and other hard structures in the body. This method gives a clearer and enhanced the image of the fetus inside the womb as the transducer is placed closer to the baby.

After the Procedure -

The procedure takes approximately 20 minutes to complete. After the procedure, the lubricant or the gel applied, can be wiped off through a soft tissue. The pregnant woman is allowed to urinate once the procedure completes. The sonographer then prints the images and gives one copy to the family. The written report also is available in another 10- 15 minutes with all the details of the fetal ultrasound clearly mentioned. The report can be discussed with the doctor in detail.

Fetal ultrasound is safe and will give results immediately. The doctor will discuss the result in detail and at the time of discussion, the family can ask any questions to better understand the results or to understand the follow up steps to be taken. If the doctor is not sure of the results, then some other tests may be advised. This might happen if any abnormalities are detected during the procedure.

If there are any birth defects observed, then the doctor will prescribe some treatment, which is to be taken either during or after the pregnancy. However, if the results are normal then it provides a confirmation that the baby is healthy and growing normally.

Fetal Ultrasound is a safe procedure, which helps to manage the pregnancy i.e. if there are any birth defects identified, then the family can decide on whether to continue with the pregnancy or terminate it. Along with the birth defects, there are multiple other important details observed as mentioned below.

  • Location of the fetus
  • Detailed examination of the head, brain, neck, spine, heart, kidneys, arms, legs, abdomen, placenta location, urinary bladder, umbilical cord, etc.
  • Number of babies
  • Weight of the fetus

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