Parents of a child with a common trisomy (T13, 18 or 21).
This information is aimed at parents who have a child, or pregnancy, affected with one of the ‘common’ trisomies:
- Down Syndrome (trisomy 21),
- Edwards syndrome (trisomy 18)
- Patau Syndrome (trisomy 13)
Most individuals will have 23 pairs of chromosomes (46 in total). A ‘trisomy’ is when you have three copies of a particular chromosome, as opposed to two. Having an extra copy of a chromosome can cause health problems. Down Syndrome, Edwards Syndrome and Patau Syndrome are called ‘common’ trisomies, because these are the chromosomal disorders which occur relatively frequently in the population.
This information can also be downloaded as a leaflet.
Do the parents of a child with a trisomy need to provide blood samples for genetic testing?
Occasionally the genetics laboratory will request blood samples from both parents to check for a Robertsonian translocation (where one chromosome is stuck onto another, but the overall amount of chromosomal material is normal). This is only required in certain circumstances. Only a small proportion of trisomies are associated with a Robertsonian translocation in a parent.
If the laboratory require blood samples from the parents, this will be stated clearly on the child/baby’s genetic report. These bloods can be sent by the clinician who organised the original genetic testing of your pregnancy or child, or via your GP. You do not need to be referred to Clinical Genetics to have these bloods taken.
What is the chance of us having another pregnancy or child affected with a trisomy?
There are no accurate estimates of the chance of having another pregnancy or child affected with a trisomy. The chance of recurrence is influenced by a number of factors, including maternal age, number of previous affected pregnancies, and if one of the parents has a chromosomal rearrangement (e.g. a Robertsonian translocation).
The increased chance of having a pregnancy or child affected with a trisomy is not limited to the one diagnosed previously (i.e. couples who have had a pregnancy or child affected with Down Syndrome, still have an increased risk of having a pregnancy or child affected with Edwards syndrome or Patau syndrome, compared to the general population).
For mothers aged 39 and under, who have had one pregnancy or child affected with one trisomy, the chance of having a baby born with Down Syndrome, Edwards Syndrome or Patau Syndrome is estimated to be 1 in 100. The chance of having a pregnancy affected with one of these conditions, which results in miscarriage, is higher than this.
From the age of 40, the chance of having a baby born with Down Syndrome, Edwards Syndrome or Patau Syndrome is estimated to be much higher, and will continue to rise with age. For example, the chance of a 40 year old mother who has already had one pregnancy or child affected with one trisomy, having a baby born with Down Syndrome, Edwards Syndrome or Patau Syndrome is estimated to be 1 in 30. Again, the chance of an affected pregnancy, which results in miscarriage, is higher than this.
The chance of having another pregnancy affected by a trisomy may also be higher if you have had more than one pregnancy or child affected with a trisomy, or if one of the parents is a carrier of a Robertsonian translocation.
Do I need any genetic testing in a future pregnancy?
If you had had one pregnancy or child affected with Down Syndrome, Edwards Syndrome or Patau Syndrome, you may be offered invasive genetic testing in a future pregnancy. Chorionic villous sampling (a sample taken from the placenta) or amniocentesis (a sample taken from the fluid around Baby) can be used to check for these conditions. Chorionic villous sampling may be undertaken from ~11 weeks gestation, and amniocentesis may be undertaken from ~15 weeks gestation.
Some parents may opt to undergo a blood test earlier in pregnancy, to screen for these conditions (Non-Invasive Prenatal Testing, NIPT). At present, this test is only accessible through private providers. Please be aware that NIPT is considered to be a screening test only, and a ‘high chance’ result, would still require follow-up invasive testing (chorionic villous sampling or amniocentesis) to confirm the diagnosis.
Although an anomaly scan during pregnancy may identify differences in Baby, which could be consistent with Down Syndrome, Edwards Syndrome or Patau Syndrome, a “normal” anomaly scan cannot exclude these conditions.
Is there anything we can do to reduce our chances of having another pregnancy or child with a trisomy?
There are no known medications or supplements which can reduce the chance of having another pregnancy or child affected with Down Syndrome, Edwards Syndrome or Patau Syndrome. However, it is important to appreciate that the chance of recurrence increases with maternal age.
In some circumstances, pre-implantation genetic testing (PGT) may be available for individuals who are carriers of a Robertsonian translocation. Couples can be referred to Clinical Genetics to discuss this.
Do I need an appointment with Clinical Genetics or genetic counselling?
Most parents will NOT require a referral to Clinical Genetics, or an appointment for genetic counselling. Rarely, you may be referred to Clinical Genetics to discuss more complex results (e.g. where a parent is a carrier of a Robertsonian translocation, or where the trisomy is “atypical”).
Other useful resources:
- Information on chorionic villus sampling: https://www.nhs.uk/conditions/chorionic-villus-sampling-cvs/
- Information on amniocentesis: https://www.nhs.uk/conditions/amniocentesis/
- Information on non-invasive prenatal testing (NIPT): https://www.genomicseducation.hee.nhs.uk/genotes/knowledge-hub/non-invasive-prenatal-testing-nipt/
- Information on Robertsonian Translocations, from Manchester University NHS Foundation Trust: https://www.mangen.co.uk/wp-content/uploads/2019/08/09-44-Robertsonian-Translocation-Aug-2019.pdf
- Down syndrome association: https://www.downs-syndrome.org.uk/northern-ireland