The latest advances in Obstetric ultrasound.
Non-invasive prenatal testing (NIPT)
The NIPT is a test by which the fetal DNA can be assessed from a blood sample taken from the mother.It has been available in Australia since 2013 and has a sensitivity of 99.9% when screening for Down syndrome.It also screens for Trisomy 18, 13 and problems with the sex chromosomes.
The NIPT can be done from 10 weeks gestation and can be done at any time in the pregnancy after this stage.The bloods are now analyzed in Australian laboratories. It takes about 10 days for the results to come to us, at which time we will notify the patients their results by phone.
The accuracy of the test is reduced when patients are; insulin dependent, have high BMI or are of less than 10 weeks gestation.
The failure rate is 8%. Failure of the test increased the chance of aneuploidy by a factor of 9 and invasive testing should be considered in patients when their NIPT has failed to give a result twice.
It is important to understand that the NIPT does not replace the nuchal translucency (NT) scan, but may be done in conjunction with it.
The 12 – 13 week scan (NT scan)
Originally introduced in 1996 as a non-invasive screening test for Down syndrome, the NT scan has rapidly developed into a test that covers much more.
Due to advances in ultrasound resolution, we are now able to use the scan as an opportunity to check the fetus for many structural defects.
This includes assessment of the fetal brain, face, heart, spine, limbs, stomach bladder and cord insertion.
In a major development it is now also possible to screen patients for pregnancy complications.
- The chance of the mother developing early onset pre-eclampsia
- The chance of the mother having a premature delivery
- The chance of the fetus having a low birth weight
The Fetal Medicine Foundation has developed this screening test using;
- Maternal blood pressure
- Maternal medical history
- Measuring the resistance in both maternal uterine arteries
- Additional biochemistry i.e. AFP and placental growth factor.
At this stage we are the only practice in Brisbane that are accredited to screen for these pregnancy complications.
If it is your preference to provide your patient with the pathology request form, please be sure to include HPlGF and AFP in addition to PAPP-A and free Beta HCG. This testing should ideally be done at 10.5 - 11 weeks gestation.
Early screening for spinabifida.
At the NT scan, we are now able to screen for the chance of the fetus having an open spinabifida.
Usually at 12 weeks the 4th ventricle is clearly visible when assessing the NT. It usually measures about 2mm and is directly posterior to the midbrain.
It cases of open spinabifida, the 4th ventricle is not visible on ultrasound. In this case the fetus could be reassessed at 15 weeks gestation, so the extent of the spinabifida could be assessed.
Traditionally when amniotic fluid was taken for testing in an amniocentesis we were only able to count the number of chromosomes present.
Due to recent advances in the mapping of the human genome, we are now able to look within the chromosomes to check for microdeletions or additions.
This information allows us to identify a number of syndromes that may be present in the fetus. This includes,
Angelman syndrome, Prader-Willi syndrome, Cri du Chat and Di George syndrome.
It also allows us to test for other variations such as cystic fibrosis.
This test is now recommended in all cases where the fetus has a major structural abnormality.
The microarray analysis is done in Australia. The results of the test take about 2 weeks to come to us following the patient’s amniocentesis.
Chorionic villi sampling (CVS) and Amniocentesis
These invasive tests are usually performed for the following reasons.
Advanced maternal age
A high risk for aneuploidy following an NT scan
A high risk result following the NIPT
A structural defect found on ultrasound
A family history of certain conditions.
The CVS is performed from 12 – 14 weeks gestation and involves taking a placenta sample under ultrasound guidance.
The amniocentesis is performed from 14 weeks on and involves taking 20mls of amniotic fluid under ultrasound guidance.
Up until recently, it was thought that the miscarriage rate for CVS was about 1%, but a recent study has shown that when the CVS is performed in a tertiary centre, the chance of miscarriage is considerably less being 0.22% or about 1 in 500.
This study also found the rate of miscarriage for Amniocentesis was also much lower when performed at a tertiary centre, being 0.11% or about 1 in 1000 (Ann Tabor, World Conference in Fetal Medicine 2016).
The first set of results are available the next working day. This is the Flourescent In-situ Hybridisation (FISH) and is considered a preliminary result.
The result tells us about chromosomes number 13, 18, 21 (Down syndrome) and the sex chromosomes. We call the patients with their results when they come through, or as their Doctor you can contact us if you would prefer to advise them yourself.
After 10 to 14 days we receive the final result. Until recently, this result just counted the number of chromosomes present, but as Microarray technology is now available, we will be ordering Microarrays on all patient's who have an Amniocentesis (see Microarray information above). The only exception to this will be in the cases of translocations. Once again we will call the patient with the result.
This procedure is generally performed when a patient presents with infertility.
It is a procedure by which the tubal patency is checked, but is also useful in imaging the uterus in greater detail than can be seen in a conventional gynecological scan.
When performed for infertility, this test is ideally done from day 5 to day 12.
This procedure is also used to check for uterine anomalies including,
It has been found that this test is not only diagnostic, but can act in a therapeutic way too. By flushing the fallopian tubes with saline, we are able to clear any mucus or debris that may be blocking them.
There is found to be a higher than average rebound pregnancy rate following this test, in the cases where no other causes for infertility has been found during the procedure.
Most patients experience mild to moderate pelvic pain during the examination, however, some patients experience no pain at all.
Analgesics are recommended one hour prior to the test.
Dr. Carmody will discuss the results with the patients immediately following the test.