If there is a history of genetic disorders then directed gene testing is often feasible prior to a pregnancy to see if either/both partners carry an affected gene with the option then of doing IVF, creating embryos, testing them and only replacing unaffected embryos. Alternatively, if natural conception has occurred and either/both parents are known to have an affected gene, then testing can be undertaken during the second trimester [>12 weeks gestation] to identify those pregnancies affected. Most times there is no history of a genetic disorder however a significant proportion of the population will carry an affected gene. As these are either recessive or X-linked genes then disease in the offspring only occurs if both parents [each not having any symptoms of the disease] pass the same affected gene onto the child in the case of a recessive disorder, or is a male in the case of an X-linked disorder.
Public health policies do not presently advocate screening for these disorders as part of routine care in infertility or pregnancy. However, there are tests that can be done on prospective parents to see if either or both carry these affected genes. More common conditions [frequency of 1:2500 -1:5000] which can be currently screened for are:
- Cystic fibrosis [affects lungs and less frequently digestion with frequent chest infections and eventually respiratory failure]
- Fragile X – commonest cause of male mental retardation.
- Spinal muscular atrophy – progressive wasting of the muscles and early death due to nerve degeneration.
This testing costs $350 with no rebate. Usually the female is tested and if returns a positive result then the male partner is tested [?at no extra cost.]
There are other tests coming onto the market which can screen for up to 500 conditions but most of these are so rare it is infrequent that both partners will carry an identical affected gene. There is an American company, Invitae, which will do saliva tests on both partners for approximately $500.
Important points about screening are that it is risk reduction, not elimination. It does not guarantee a normal child. Some diseases detected have unknown or unpredictable clinical outcomes. If a potential affected gene is found then there is the extra cost of counselling and review by a geneticist along with the issue of test disclosure to your partner and family. There may be issues with life and health insurance if found to be a carrier [currently not thought to be a problem].
If both partners are found to have an identical gene defect then options include doing IVF and testing the embryos and only transferring unaffected embryos, or conceiving naturally and doing testing at 14-16 weeks and having the option of discontinuing the pregnancy or using donor sperm/eggs.
While currently not part of routine screening, these tests are available if so desired and can be ordered if you wish. Obviously, if affected genes are found then this does in itself create emotional stress and anxiety on which course of action to take.
Dr Ross Turner ph 33711133 (created 28.08.18)