Dating Scan during Pregnancy: Procedure, Accuracy & Drawbacks

Dating Scan in Pregnancy – What to Expect

Medically Reviewed By
Dr. Sabiha Anjum (Gynecologist/Obstetrician)
View more Gynecologist/Obstetrician Our Panel of Experts

There are two types of pregnancies. Those that are planned and those that just happen. Pregnancies that are spontaneous will often make you wonder when it happened. Apart from satiating your curiosity, it has other health-related implications. For instance, there are cases where doctors have unnecessarily induced labour because there is uncertainty about how old the foetus is. This can result in premature birth.

This isn’t to say that those who have had a planned pregnancy can be 100 percent accurate. Barring the incredibly meticulous, tracking the exact time of conception can be, at best, a guessing game.

What is a Dating Scan and Why it It Done?

A dating scan is a method that is used to reliably assess the age of a foetus with a maximum error of 3 to 5 days. A dating scan is for women who have the following issues:

  • Not all menstrual cycles happen like clock-work. While some come early, there are others that come a bit later. If the last menstrual cycle was irregular, it would help in removing any margin of error that exists.
  • Women who have infrequent periods on a regular basis would benefit the most from this test. As the 28-day rule is never followed, the exact age of the foetus would be difficult to assess through conventional methods.
  • Breastfeeding acts as a natural contraceptive for up to 6 months. However, if you become pregnant during this time, a dating scan becomes useful.
  • Women who are on oral contraceptives but still become pregnant, would not know their ovulation cycle. This would make it difficult to determine the age of the foetus.

When is the Pregnancy Dating Scan Recommended?

  • The first dating scan is usually done after 10 weeks, and this is the norm all over the world.
  • This doesn’t mean that you cant do a dating scan at 8 weeks either. There are many moms who have done the same and have had accurate results.
  • Women who have a history of complications when it comes to pregnancy can go for it earlier. For instance, those with previous pregnancies who have suffered from a miscarriage or bleeding, a dating scan at 6 weeks is needed.

How is It Performed?

The dating scan is done with the assistance of an ultrasound machine. You’re required to expose your belly on which a gel will be applied. After this, a device called the transducer is gently navigated across the belly to do the mapping. This procedure can take anywhere from 20 to 30 minutes. You will need to drink water before the scan as a full bladder is one of the preconditions for taking this test. This is so because the bladder thrusts the uterus upwards giving the sonographer good visibility of the womb. If required, a vaginal scan can also be done.

What Does a Dating Scan Ultrasound Reveal?

A dating scan at 7 weeks can be performed to reveal:

  • The heartbeat of the foetus
  • The presence of fibroids
  • The developing limbs of the foetus
  • Movement of the foetus
  • It can detect umbilical cord issues as well as deformities in the baby’s skull
  • It can indicate the presence of twins or triplets
  • Some internal organs like the stomach can be also be seen. However, it is not equipped to look at the functioning of internal organs in a detailed manner.

What Does a Dating Scan Ultrasound Reveal?

How Accurate Are Dating Scans?

Early dating scan accuracy is reliable to a remarkable degree. However, the system isn’t fool-proof, and there are situations where accuracy can be compromised. Some of these situations include:

  • The skill of the sonographer is an important part of the equation. If the proper procedure isn’t followed, you may end up with the wrong results! If you have someone who is inexperienced or seems unsure about what they are doing, try going for a second opinion.
  • A sonographer can only be as good as his equipment. There may be instances where the instruments used have not been maintained properly or developed a problem. This can result in a faulty reading.
  • The position of the foetus can be a disadvantage during the scan. While sometimes they might be stretched out, other times they could be curled or in an awkward position which makes an estimation difficult.
  • Genetics may mean that growth could be varied and not be based on the mean measurement. For example, a 10-week foetus may be developing at the rate of an 8-week foetus, only to develop later at a faster rate. This can lead to the sonographer coming up with the wrong reading.
  • If the dating scan is performed after 12 weeks, the margin of error increases. This is because there is a limited movement by the foetus before this.

Can You Perform Screening Tests and Dating Scans at the Same Time?

This is technically possible but depends on what type of ultrasound machine is being used. While some have a provision for doing screening tests, others do not.

You can use a screen test to see if your child is likely to have Down’s syndrome. This is done with the help of a Nuchal Translucency (NT) scan along with a blood test. Together, both these tests are known as the combined screening test.

For the combined screening test, it is imperative that you do a dating scan first. This is because the hormones in the body change based on what stage you are at your pregnancy.

Are There Any Drawbacks of Having Dating Scan during Pregnancy?

While the benefits of having a dating scan are obvious, it is important to stay calm.  A minor issue that will not have a bearing on the pregnancy can be blown out of proportion in the mind of the mother. This would cause unnecessary worry and stress to the mother who should be in a calm state of mind during pregnancy.

Dating scans help you understand the time of conception if you have an unplanned pregnancy or are not sure about when exactly you conceived. If you’ve been recording your cycles and have been able to predict the time of conception, you’re safe. However, those of you who haven’t, don’t fret, as the dating scan can help you with this!

Also Read: Ultrasound Scans during Pregnancy

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