Ultrasound – which lets us safely examine your unborn baby – has revolutionised obstetrics. We can diagnose problems and keep a close eye on baby’s wellbeing, in a way that wasn’t possible for your mother or grandmother.
Most women in Australia have a number of pregnancy scans. We perform scans at different times because each scan has a different purpose:
- Dating scan
- Nuchal translucency (NT) or Early Anatomy (EA) scan
- Fetal anatomy (morphology) scan
- Growth and wellbeing scans
Women with high-risk pregnancies, for example twins, need more frequent scans.
The Dating Scan
A dating scan is usually performed between 8 and 10 weeks. It confirms your due date, excludes ectopic pregnancy and diagnoses twins. If you have abdominal pain or bleeding, an earlier scan may be appropriate.
The Nuchal Translucency
Nuchal translucency (NT) scan is an optional scan plus a blood test. It’s for couples who choose to screen their baby for the common fetal chromosomal problems (Down, Edwards and Patau syndromes). It’s performed from 11 to 14 weeks. You can read more about the screening tests here.
Early fetal anatomy (12-16 weeks) scan
As ultrasound gets better, we can examine fetal anatomy earlier and earlier. An early anatomy scan isn’t essential for every woman, and there are many problems we can’t detect until 18-20 weeks. However, many couples choose to have an early scan for extra reassurance. It’s also recommended for:
- Couples with a previous child affected by an anatomical problem
- Twin and triplet pregnancies
- Women with chronic medical problems (such as diabetes) or taking certain medications
The fetal morphology (18-20 weeks) scan
The fetal anatomy or “morphology” scan is the most important ultrasound of the pregnancy. Every woman should have this scan. The ultrasound takes place between 18 – 20 weeks and takes approximately 30 minutes. I strongly recommend that you see a team who specialise in obstetric imaging for this scan.
The aims of this scan are to:
- Detect common abnormalities in the baby’s anatomy
- Look for “soft markers” for chromosomal disorders
- Check the baby’s size
- Check the fetal gender (if the parents wish and the baby co-operates!!)
- Monitor growth and look for early problems in a twin pregnancy
- Measure cervical length in women at high risk of premature birth
- Take nice keepsake pictures for the parents and family to enjoy!
However, it’s also important to realise that there are limits to what we can pick up on this scan:
- The anatomy scan only provides information on fetal anatomy, not childhood development. It does not tell us anything about behaviour, intelligence or personality.
- Some fetal structural or genetic problems are very subtle and may not be visible on ultrasound scan, or may only develop after birth.
- The ability to detect fetal problems depends on the image quality. Sometimes babies lie stubbornly in the same position and it is not possible to see all the anatomy – the scan may need to be repeated later that day or another day. Also, image quality may not be as good in women who are overweight.
Growth & Wellbeing Scans
Traditionally, women with low-risk pregnancies were not offered any further ultrasound scans after 18-20 weeks. We relied on feeling your pregnant belly and “guesstimating” the size of the baby. However, this old-fashioned approach misses a lot of potential concerns.
Ultrasound has proven benefits over clinical examination, and I recommend that all women have at least one 3rd trimester fetal growth and wellbeing scan. Women with high-risk pregnancies will often need more than one 3rd trimester scan.
The aims of the scan are to:
- Measure the size of your baby and track their growth
- Check the placenta and amniotic fluid
- Perform special tests called Dopplers. Think of Doppler ultrasound as a way of checking on baby’s wellbeing. In modern fetal medicine, Dopplers may detect a problem before we see a change in the baby’s size.
Approximately 1-in-100 fetuses have some form of congenital heart disease. A fetal echocardiogram (ECHO) is a detailed examination of the baby’s heart. Ideally, it’s performed at 22-24 weeks.
A fetal ECHO is recommended for:
- Previous baby or family member with congenital heart disease
- Pre-pregnancy (type I or type II) diabetes
- Monochorionic twin pregnancies
- Other fetal abnormalities picked up on the routine anatomy scans
- A thickened NT measurement at the nuchal translucency scan
- Women taking certain medications e.g. anti-epileptics