Your guide to pregnancy scans

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During your pregnancy you’ll have a few precious opportunities to check in on your unborn baby. These pregnancy ultrasounds give you an exciting glimpse of your growing bub and, most importantly, they give your care provider an idea of your baby’s health.

Dating scan

This is one of the first scans you may have. It is done to check the size and likely age of your baby. Dating can be important in picking up if you are ‘overdue’ or if your baby appears too big or small for the dates according to your periods. It can also pick up twins and detect abnormalities with the uterus, such as fibroids, that may impact labour.

The dating scan can be performed as early as week five of the pregnancy, if you really don’t know when you conceived or sometimes if you have had a miscarriage before or had some bleeding. For most women dating is done around 11 to 13 weeks of pregnancy during the nuchal translucency scan, where it’s just as accurate.

Related: What to expect at the ultrasound

Nuchal translucency scan

This is an ultrasound in which the fluid-filled space at the back of bub’s neck is measured. The thicker the nuchal translucency, the higher the risk of a problem, especially Down syndrome. Other chromosomal problems and heart problems can also be detected from a thicker nuchal sack.

This scan is combined with a blood test, called the ‘triple test’, which looks at the levels of three components in your blood.

The first is a protein called alpha-fetoprotein (AFP), which is produced by bub, the second is beta human chorionic gonadotropin (beta-hCG), a hormone made by the placenta, and the third is estriol (E3), a hormone produced by both your
growing baby and placenta. High levels of AFP may indicate a neural tube defect in bub, such as spina bifida, while low levels combined with abnormal levels of beta-hCG and E3 can indicate chromosomal abnormalities.

Combining the triple test with the ultrasound scan means we can pick up 85 to 90 per cent of babies who have Down syndrome, compared to 70 per cent or less using the scan on its own.

Most women will receive a ‘low risk’ result with these screenings, but about five per cent of pregnancies will be positive and require further investigations. The good news is, many of these pregnancies will lead to healthy babies.

Related: When should I have my first pregnancy scan?

Morphology check

Between 18 to 20 weeks you’ll have the morphology scan. At this stage your baby is well developed enough to let us have a good look at his organs and skeleton, but it’s still early enough to give us options in management if an issue is picked up.

It’s also a good time to check on your placenta to make sure it’s in a healthy position and that there’s a good amount of amniotic fluid.

The ultrasound specifically looks at your baby’s brain, face, spine, heart, lungs, stomach, kidneys, bladder, arms and legs, as well as the cord insertion at his belly button.

At this stage it’s often possible to determine the sex of your baby. Sometimes bub’s position can make it difficult to tell, though. If you want to find out let the sonographer know, but don’t go and buy the entire blue section of your local baby shop, just in case!

Related: Your pregnancy week by week

Are scans safe?

It’s the question plenty of mums-to-be have: are ultrasounds safe? Rest assured that ultrasounds have been performed for decades and are done so often, and we don’t have any evidence that they are harmful to you or to your baby.

While they’re safe, they may not always be comfortable, particularly if you’ve been asked to come to the scan with a full bladder! My advice is to drink an extra couple of glasses of water the night before the scan then, on the day, stick to three or four glasses of water to avoid having your bladder feel like it’s going to burst.

My second bit of advice for making a scan as comfortable as possible is to take your partner, a family member or a friend with you for support. Seeing your baby on the screen is usually a very exciting, heart-warming experience that’s lovely to share with someone you love. And on the very small chance that you receive bad news, having a support person there can make a big difference.

Related Gallery: Ultrasound: Baby's development in 2D and 3D?