PRENATAL SCREENING
All pregnant women are routinely offered ultrasound scans at 11-13 weeks and 18-22 weeks to check the development of the pregnancy. This services are only available during office hours on Monday till Friday.
The 11-13+6 weeks Nuchal Translucency (NT) scan:
· Confirm your baby’s heart is beating.
· Check when your baby is due.
· Find out whether you are having twins.
· Screen for Down syndrome and other chromosomal abnormalities.
· Detect some major structural problems.
· Screen for pre-eclampsia (high blood pressure that typically develops later in the pregnancy).
What is Down Syndrome(T21)?
Down syndrome is a genetic condition associated with moderate intellectual delay. Children with Down syndrome have characteristic facial features and some have problems with the heart or the digestive tract. Down syndrome is caused by the presence of an extra chromosome (number 21) in all the body’s cells. There is no cure for Down syndrome, but many symptoms can be treated and with early intervention children with Down syndrome can be helped to reach their potential. Down syndrome is the commonest form of intellectual delay seen in children. It occurs in all races and cultures at around the same rate. Approximately 1 in 1000 infants born have Down syndrome.
Do I want a
screening test for Down Syndrome?
Not all women want to have a screening test for Down syndrome – as the information would not affect decisions they would make about their pregnancy. This is a very personal decision and we respect the fact that not all couples would want to have this test.
Combined First Trimester Screening Test(FTS)
FTS involves an ultrasound scan and a blood test at 11-13+6 weeks pregnancy. The ultrasound examines the fluid-filled space at the back of a baby’s neck, called nuchal translucency (NT), and the development of the baby’s nasal bone (NB). The chance of Down syndrome is higher if the NT measurement is thicker and/or if the nasal bone is not readily visible. The blood test measures the levels of two proteins in the mother’s blood: PaPP-A ( pregnancy associated plasma protein A) and Free-βhCG (free-beta human chorionic gonadotropin.)
Your age, the NT and NB measurements and the blood test results are combined to develop a risk that describes how likely it is that the baby is chromosomally normal or has Down syndrome.
If the adjusted risk is less than 1 in 1000 (0.1%) it is considered very low risk. Most women have a very low risk result.
An adjusted risk >1 in 300 (0.3%) is considered an increased risk.
5% of women (1 out of 20) get an increased risk result and may choose to have further testing (NIPT/ NICC, CVS or amniocentesis). Most babies at increased risk of Down syndrome are completely normal. If the risk result is increased, we will message you directly to inform you and discuss your options.
Second Trimester Screening – Triple Test
If you miss combined first trimester screening (done between 11 and 13+6 weeks) you can have a triple (blood) test at 15-18 weeks. This test uses biochemical markers alone, but is still quite robust, and will identify 70% of affected pregnancies. Alternatively, you can opt to have the NIPT test, which will identify >99% of babies affected by Down syndrome.
Increased nuchal translucency /Screening for cardiac defects
One of the sonographic features examined for Down syndrome screening is also known to be abnormal in fetuses that have other structural problems, such as cardiac defects. If the NT is increased (broadly speaking above 2.5mm) then we will arrange for you to have a fetal echocardiography by peadiatric cardiologist at 16-18 weeks to check the babies heart development more carefully.
The 18-20 weeks scan:
This ultrasound will check that your baby is growing and developing normally. This scan can assess your baby’s development with great detail, but it cannot detect all problems or abnormalities. Unfortunately a normal ultrasound does not guarantee that your baby will be normal nor does it guarantee that you or baby will not develop complications during your pregnancy. A normal ultrasound is reassuring for parents and doctors, but it is not perfect.
Unfortunately a normal ultrasound does not guarantee that normal scan does not mean the baby does not have any defect. Not all major structural abnormalities can be detected on ultrasound scan nor subtle abnormalities eg isolated hole in the heart, cleft palate, anal atresia, various heart defects including total anomalous pulmonary venous drainage and late onset structural abnormalities eg congenital diaphragmatic hernia, trachea-esophageal fistula, biliary atresia. Primary pulmonary hypertension of newborn or Persistent ductus arteriosis only detected at birth only.
Normal scan does not mean you or baby will not develop complications during your pregnancy. Therefore advised to get prenatal insurance during each pregnancy from 16 weeks onwards.
Problems such as cerebral palsy, learning difficulties or autism are currently not able to be detected on ultrasound, as they are not associated with structural changes in the baby.