Nuchal Translucency scan – consider carefully first

Three patients recently had nuchal translucency Nuchal Translucency scanscans with serum checking to reassure that baby was at low risk of Down syndrome (Trisomy 21).

All had high risk results. One baby has a 1 in 8 risk of Down syndrome, the second 1 in 38 and the third 1 in 138 risk of Down syndrome. All three have decided not to take it further as they would not entertain the idea of termination of pregnancy if baby has Down syndrome.

To check baby’s chromosomes with either a chorionic villus sampling (CVS) or with amniocentesis puts them at about 1 in 200 to 1 in 300 risk of miscarriage because of the invasive nature of the testing. There is the real possibility of losing a perfectly normal baby because of a test being done.

Nuchal Translucency scanThere is the possibility of causing a miscarriage and being told that your baby is normal and does not have Down syndrome. You have to live with the knowledge that if you had not had the test you would be cuddling this baby that you lost. Neither patient is prepared to accept this miscarriage risk, especially as neither would proceed with a termination of pregnancy even if the baby had Down syndrome.

There can be further indirect checking for Down syndrome at the morphology scan, but they will not know everything is ok and baby does not have Down syndrome until baby is born.

So the test that these patients did to reassure has backfired and now they are more anxious then they would have been had they not had the test done to start with. This is likely to detract from their enjoyment and excitement of pregnancy.

My advise is think very carefully before deciding on a Nuchal Translucency scan. If you would not have a termination of pregnancy if the baby had Down syndrome then I recommend don’t get the test done.

Some say it will prepare them if they know baby has Down syndrome.  I have a ‘yes’ and ‘no’ answer to that comment. ‘Yes’ you will know, but ‘no’ it won’t really prepare you as Down syndrome is such spectrum and you may be preparing for something much worse than is the case. Again I predict the knowledge will result in a heightened level of anxiety in your pregnancy and detract from your enjoyment of your pregnancy experience.

There is now a newer test called the NIPT (non-invasive prenatal test) to check for Down syndrome and other chromosomal abnormalities in your baby by checking placental (baby) DNA in your blood. Your blood is collected (so there is no risk of miscarriage) and the cells free DNA of your baby’s placenta in your blood is checked for the commonest chromosomal abnormalities (Trisomy 21, 13 and 18). It is not a ‘1 in ….’ result but a ‘yes’ or ‘no’ where no means <1 in 10,000 risk and so is extremely accurate. The NIPT cost has come down and is now $425 through Douglass Hanly Moir (Harmony Test).

The NIPT can also check for sex chromosome disorders and in doing so will be checking the sex of your baby. So you can if you wish find out the sex of your baby with a NIPT. On the other hand, you can’t find out the sex of your baby through a NTS check.

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Posted by Dr Gary Sykes on - Tests in Pregnancy

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