Pregnancy ultrasound: the facts

Pregnancy scans and how good they are these days

Is there a baby on the way? Learn more about 2D, 3D and 4D scans, and what they can do to ensure you give birth to a healthy baby.

Ultrasound scanners are amazing tools used to view the developing foetus during pregnancy. The great thing about this technology is that it doesn’t expose you and your unborn baby to radiation (as with X-rays).

The majority of specialists, and even a substantial number of GPs, make use of this technology to show expecting parents what their baby looks like: how he sucks his thumb, yawns, moves his hands and legs and kicks while he’s still snug in the womb.

So, how does it all work?

Ultrasound explained
Ultrasound is high-frequency sound that’s generated electronically by a machine and special crystals in a probe. The sound travels through the body, and bounces off different tissues and back to a receiver on the same probe. These sound waves are interpreted into a digital image.

Although extremely useful, traditional, standard 2D scans produce black-and-white images that are streaky and blurry, making it difficult to see the baby properly. This is one of the reasons why 3D and

4D scans have grown in popularity.
3D scans show still pictures of the foetus in three dimensions (sound waves are sent at different angles through the womb), while 4D scans show moving 3D images of the baby. In other words, 4D scans allow for 3-dimensional pictures in real time.

Two crucial ultrasound scans are performed at 13 and 22 weeks of pregnancy. A 3D or 4D scan is best performed between weeks 26 and 30 of pregnancy.

Many observations are made during these scans. The ultrasound is used to confirm that the foetus is in the right place, inside the uterus, as opposed to an ectopic pregnancy where the foetus has implanted in an abnormal area. Other findings of importance are:

  • To establish the presence of a living embryo/foetus.
  • Determine if there are multiple pregnancies.
  • Estimate the age of the pregnancy.
  • Evaluate the position of the baby.
  • Evaluate the placenta, including its position.
  • Determine the amount of amniotic fluid around the baby.
  • Evaluate the cervix for opening or shortening thereof.

More than pretty pictures
2D and 3D/4D images also have another important function: in trained hands, these images can and should reveal foetal abnormalities.

Congenital abnormalities involving the skeleton, brain, spinal cord, fluids and the heart can all be detected. The images offer an accurate prenatal diagnosis for a range of abnormalities, including:

  • Down syndrome
  • Spina bifida (where the baby’s spinal cord fails to develop properly)
  • Hydrocephalus (the build-up of fluid in the brain)
  • Dwarfism
  • Malfunctioning kidneys
  • Heart defects

If you keep in mind that more than 90% of foetal abnormalities occur in pregnancies where both parents are completely healthy and where neither have a family history of defects, it’s clear that ultrasound is an incredibly important tool in ensuring a healthy pregnancy.

How should I prepare?
Wear loose-fitting clothing, as the examiner needs to have access to your abdomen. You may be asked to wear a gown. If it’s early in your pregnancy, you may be requested to have a full bladder for the examination. After about three months, a full bladder is usually no longer required.

How is the procedure performed?
As you lie on the examination table, the radiologist or sonographer will spread warm gel on your skin and press the transducer firmly against your body, moving it back and forth over the area of interest until the desired images are captured. They will regularly stop to measure the size of the foetus.

The examinations are by and large painless, fast and easy. Occasionally a trans-vaginal ultrasound examination will be required. During this exam, an ultrasound probe is inserted into the vagina and the images are acquired this way.

Are there any risks?
There has not been a single documented case of damage to either a child or mother as a result of an ultrasound examination. Occasionally it has been noted that the examination wakes the sleeping foetus, but nothing else of note has been reported. The benefits of these examinations are extensive.

Are there any limitations?
Ultrasound scanning can’t detect all foetal abnormalities. In cases where abnormality is suspected but not detected ultrasonographically, further testing like amniocentesis or chorionic villus sampling may be required.

Who should perform the scan?
It’s best to get your scan done by a foetal-medicine specialist whose level of skills adheres to the standards of the Foetal Medicine Foundation (FMF) in London. Doctors accredited by the FMF are audited every year to ensure their skills remain up to standard.

Ask your doctor whether he or she has FMF accreditation.

What will happen with the results of the examination?
Before the scan is performed, you’ll be asked if you want to know any of the results. The doctor who referred you for the examination will discuss the results with you after the scan.

Is it confidential?
Yes, like all medical examinations, your name, medical condition, and any particulars about your life will not be made public in any way. The person performing the scan may record on paper, or digitally on the machine’s hard-drive, certain pictures to help them or colleagues refer back to the aspect they were interested in.


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