Obstetric Ultrasound is a scan that is carried out during antenatal period, that is, during pregnancy, to monitor the mother and baby.

It allows monitoring of the different stages of intrauterine life, assessing the placenta, the amniotic fluid that surrounds the fetus, and monitoring the baby’s development from the first weeks until birth.

It is also possible to determine the gestational age and the probable date of delivery using ultrasound.

Using ultrasound, it is possible to detect some problems and fetal anomalies, which if diagnosed in time, can help avoid complications that endanger the life of the mother & fetus.

Frequently asked questions about Ultrasound in pregnancy

Is ultrasound in pregnancy safe?
Does it have any side effects??

UItrasound is a completely safe technique for the mother and her baby. It doesn’t have any side effects or adverse effects for either the mother or the baby.

Does ultrasound use radiation or emit rays (like Xrays) ?

The technique of ultrasound is very different from X-rays and does not use any harmful radiation.

Ultrasound rather uses sound waves which are beyond the audible range. These sound waves are directed towards the mother’s abdomen by the ultrasound probe and get reflected back from the fetal and maternal structures. These are gathered back by the probe and processed by the ultrasound machine to form an image of the fetal and maternal structures.

  • How many ultrasounds should a woman undergo in pregnancy?

(Minimum how many & Maximum how many??)

Any pregnant women should undergo minimum 4 ultrasound scans as follows:
1.At 6-8 weeks of pregnancy: Early pregnancy scan or viablity scan- to confirm fetal cardiac activity (& for dating).
2.First trimester screening scan/ NT NB scan (Level 1 scan)- at 11 to 14 weeks – also for congenital/chromosomal anomalies.
3.Anomaly scan/TIFFA scan (Level 2 scan)- at 18 to 20 weeks
4.Growth & Doppler scan (after 30 weeks)

There is no limit on the maximum number of ultrasound that a particular pregnancy may require.

A high risk pregnancy may need very frequent ultrasound & doppler examinations to assess the progress & accordingly take decisions relevant for patient management

What are the types of Ultrasound studies in pregnancy  (trimester wise):

First-trimester ultrasound

There are generally two ultrasounds offered during the first 3 months (First trimester) of pregnancy:

  1. Early pregnancy scan or viablity scan (At 6-8 weeks of pregnancy): Helps to confirm and determine pregnancy age, hence the name dating scan. This pregnancy scan can detect the baby’s heartbeats and any source of internal bleeding or abnormality found in the uterus that might affect the pregnancy.It also confirms the location of pregnancy and checks if it is inside or outside the uterus. Pregnancies outside the uterus are called ectopic pregnancies. Such pregnancies need early diagnosis and immediate medical attention. Twin pregnancy or multiple pregnancies can also be detected at this stage.

The dating scan is very important as it establishes a benchmark which will enable accurate assessment of fetal growth as the pregnancy progresses in the 2nd & 3rd trimester.

2. Nuchal Translucency Scan (NT/NB ultrasound pregnancy scan)

(11 week to 13 week 6 days ultrasound scan): Most suitable time is 12-13 weeks

“Nuchal” is the adjective for the “nape of the neck”, and translucency here refers to the translucent area in that portion. The fluid at the back of your baby’s neck is checked by this scan. The NT scan looks at the entire spinal column of the baby, measures the size and thickness of its nuchal translucency. NT is increased in up to 40% of fetuses that have a major cardiac abnormality and is associated with other structural and genetic anomalies.

This scan also checks for the presence of nasal bone.The nasal bone is ‘absent’ or hypoplastic in 50–60% of fetuses with trisomy 21.

Alongwith this sonography, a double marker blood test is recommended. This sonography and double marker blood test guides obstetricians to rule out chromosomal abnormalities like Down’s syndrome.

We routinely perform uterine artery doppler as part of NT/NB scan. This helps us prempt possiblity of increased blood pressure and related complications in the mother and growth issues in baby in later pregnancy.

Second-trimester ultrasound


3. Anomaly scan/TIFFA scan (Level 2 scan)- at 18 to 20 weeks

An anomaly scan or TIFFA scan (Targeted Imaging for Fetal Anomalies) is the most essential pregnancy scan carried out in your second trimester.

The anomaly scan assesses the baby’s structural anatomy & internal organs from head to toe in adequate detail. Besides recording the fetal size & weight, a detailed anomaly scan can help in timely detection of a variety of major congenital anomalies/malformations. For this, special attention is paid to the brain, face, spine, heart, stomach, bowel, kidneys, and limbs..

During the anomaly scan, we also assess the position of placenta, the umbilical cord, and amniotic fluid around the fetus. A uterine artery doppler is also an essential part of the study.

  1. Fetal Echocardiography

This ultrasound is meant to check the structure and function of a baby’s heart.

This is one of the optional sonographies during pregnancy. This pregnancy ultrasound scan is recommended typically in high-risk pregnancies. It’s typically done in the second trimester, between weeks 18 to 24.

This scan looks out for abnormalities such as holes in the heart, narrowing of arteries, valves that don’t open and close properly. The common indications for fetal echocardiography include:

  • Mother having a heart defect
  • Mother already has had a baby with a heart defect
  • Diabetic mother: a slightly higher risk of having a baby with a heart defect
  • History of consuming certain drugs that can increase the risk of heart problems, such as some antiepileptic medications
  • Abnormal nuchal translucency (NT) scan with normal chromosomal study

Third-trimester ultrasound

In the last 3 months of pregnancy, ultrasound is used to monitor the baby’s health, growth, development, and internal organs. Changes in the uterine environment are also carefully assessed. Following are the pregnancy ultrasound scan prescribed in the third trimester :

  1. Third Trimester growth & Fetal well being scan: besides fetal growth & anomalies, the position of placenta & amount of amniotic fluid is assessed. The lower end of the placenta should not be lying too close to the cervix. In the case of twins or triplets, there is a greater chance of developing growth problems, which is checked by the growth scan.
  2. Obstetric Doppler scan: A proper blood flow to the uterus, placenta, and the umbilical cord is crucial for a baby to develop normally inside the womb during pregnancy.

A routine pregnancy ultrasound alone is incapable of demonstrating the blood flow. It is complimented by color doppler which looks at both the maternal vessels (uterine arteries) & fetal vessels (umbilical & middle cerebral arteries in most cases). This helps identify & quantify deficencies in maternal & fetal blood flow which are important to guide further management in this final trimester.

List of documents/information needed for any ultrasound done on a pregnant women (as per guidelines of PC/PNDT Act):
1. Identity proof of patient having full name (eg. Aadhar card) matching the prescription
2. Date of first day of last menstrual period (LMP) of pregnant lady
3. Proper prescription by referring doctor mentioning indication for ultrasound- valid only for 21 days from date of issue
4. Prescription to have full name of referring doctor
5. Prescription to have proper stamp of referring doctor with DMC number

Dr. Anuj Thakral

Dr. Anuj Thakral started his informal medical training at home...

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