Ultrasound in pregnancy

What is an Ultrasound scan?

Ultrasound scan is a very useful, comprehensive and painless diagnostic imaging test, done with the help of a machine called ultrasound machine. The ultrasound machine is a large computer like machine with transducer probes that produce high frequency sound waves to produce images of structures inside your body. These images help clinicians to assess your internal organs and diagnose various clinical conditions without even inserting a needle. Hence it is a non-invasive test and is known by various names like ultrasonography, sonography, ultrasound, ultrasound scan or simply scan. Ultrasound in pregnancy is done for various reasons, as we will see below.

Why is ultrasound needed in pregnancy?

Ultrasound is an investigation in which ultrasonic sound waves are used for detailed assessment of your pregnancy. It is an essential part of your pregnancy checkup and provides in depth assessment of the fetus and the uterus. Some of the things that are assessed by an ultrasound in your pregnancy are:

To confirm if you are pregnant
Evaluation of overall growth, health and development of the fetus
Baby’s gestation age can be determined and due date can be calculated
To find out if the pregnancy is singleton, twins or triplets, or multifetal pregnancy
To find out if the dates of your last missed period are correlating well with the growth of the pregnancy or not.
To find out the location of the placenta. There are some locations at which the attachment of placenta, makes your pregnancy high risk during delivery. Knowledge of placental position helps your obstetrician to make your delivery plan well in advance to minimize the risks.
Helps in early detection of developmental defects in the baby.
To find out the oxygenation and the blood flow to the fetus
Helps to detect any abnormal pregnancy like molar pregnancy or an ectopic pregnancy
Amount of amniotic fluid can be assessed
Any growth or abnormality of the uterus or ovaries can be found out
It helps to check baby’s position in your uterus
Fetal weight can be estimated

Who will do my ultrasound?

Your obstetrician, radiologist or radiology technician (not in all the countries) may do your pregnancy ultrasound, depending on the local laws and prevalent practices in your country.

How is an ultrasound done?

An ultrasound is done at an ultrasound scanning center. In the ultrasound room, you will see a large computer like machine called ultrasound machine. You will be made to lie down comfortably on ultrasound table, and then a water based gel like material called jelly is applied on the skin above the parts to be scanned. Then your abdomen or parts are scanned using a transducer or probe which is connected with the wire to the ultrasound machine. This transducer produces sound waves which reach your organs and detects the reflected sound waves from the organs to produce the images.

It is a painless procedure and feels as if somebody is just touching you on your abdomen.

When do you get your first ultrasound?

First ultrasound: The first ultrasound is done at about seven to eight weeks of pregnancy to look for:

Fetal heartbeat: Confirms pregnancy, also confirms presence of live fetus (viability of pregnancy)
Helps to verify your due date and confirm your gestational age
To check the length of fetus
To check if it’s single baby, twins, triplets or multiple babies
To look for ectopic pregnancy: Sometimes, pregnancy gets accidentally lodged into fallopian tube instead of uterus. This is called ectopic pregnancy.

Since this scan helps to check the viability of the fetus and also to confirm your gestational age, it is also known as Viability ultrasound or Dating ultrasound. The fetus is very small at this stage, so this scan is done transvaginally. This means that an ultrasound probe is inserted through the vagina to have a closer look at the fetus. It is not at all painful; so don’t worry. The timing of this scan may vary up to 10 weeks depending on the practice in your country and on the choice of your obstetrician.

How many ultrasounds are done in pregnancy?

After the first ultrasound, subsequent ultrasounds are planned as follows:

Nuchal Translucency scan (NT Scan): This is a special category of ultrasound that is done between 11 to 13 weeks of pregnancy to find out if the baby is at high risk of chromosomal defects, mainly Down Syndrome (Trisomy 21). The baby born with such chromosomal disorders suffer from mental retardation, physical defects, delayed development, heart diseases, intestinal diseases, and low life expectancy. This scan measures the amount of fluid present in a small space behind the neck of fetus. All fetuses have some fluid in this space but greater amounts of a fluid indicates towards chromosomal disorders. The nasal bone of the developing fetus is seen and measured, along with many other markers of chromosomal defects. It also gives information about the placental implantation and blood flow in the uterine arteries which speaks about the adjustment of the pregnancy in the uterus. It is known as uterine artery doppler. Low blood flow in these arteries tells that there is high likely hood of development of gestational hypertension in mother or growth problems in the baby in future.
Level 2 ultrasound or Anomaly scan or 20 weeks scan: This ultrasound is typically performed between 18 to 23 weeks of pregnancy, most commonly at 20 weeks. This is the most important ultrasound in pregnancy and done to rule out fetal malformations. During the ultrasound, your doctor will examine the baby’s anatomy to check for congenital developmental defects like cleft lip, cleft palate, congenital heart defects, anomalies of brain/spine/kidney etc. In addition, placental location, amniotic fluid assessment, measurement of cervical length, uterine artery doppler are also done. This scan is done transabdominally and takes some time. But it’s important; so be patient!
Growth scans: Sometimes, there are concerns regarding the proper growth of the baby if the mother is hypertensive, diabetic, obese or has kidney or heart disorders. In such cases, growth scans are done at regular intervals to ensure that the growth of the fetus is as per gestational age. They are also done in cases where the earlier scans show a placental insufficiency or there is a mismatch between the gestational age and the age of fetus calculated by ultrasound. In such cases, a growth scan assesses whether the baby is growing well or not, whether it is receiving good blood flow, the amount of amniotic fluid is normal or not, the position of the baby, estimated weight of the baby and the present placental position if it was previously low lying. It may be done at regular intervals (28, 32, 36 weeks) or as deemed appropriate by the treating obstetrician.
Fetal ECHO: Fetal Echocardiography is done to scan the heart of the fetus at 18-24 weeks, to look for any heart defects in the developing fetus. This is not done in all patients. It is recommended by your obstetrician in patients who are elderly mothers, hypertensive, diabetic, smoker, alcoholic, found to have abnormal NT Scan, have another baby with heart defects, have a family history of congenital heart defects. It is done so that if any defect is detected, a treatment plan can be formulated for later or if it’s untreatable or incompatible with life, timely decision can be taken to terminate the pregnancy.

Will Ultrasound rays harm my baby?

This is a very frequently asked question. No, the ultrasound waves do not cause any harm to you or to your baby. They are just sound waves that we can not hear. Sound waves emitted by the transducer are reflected back by the baby and picked up by the probe to generate an image on the screen. It’s as simple as that!

What are the different methods of doing an ultrasound?

Pregnancy ultrasound can be done by two methods:

Transabdominal technique: In this method, an ultrasound probe is placed on your tummy (abdomen) to do the scan.
Transvaginal ultrasound: In this method, an ultrasound probe is introduced into the vagina and imaging is done. It gives a very good clarity in early pregnancy as the fetus is very small. It is painless, although some amount of discomfort may be encountered during the introduction of the probe.

Stay healthy and have a beautiful journey in your pregnancy!

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