NIPS (Non Invasive Pre Natal Screening) and Serum Screening are commonly performed tests for screening for Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), Trisomy 13 & Monosomy X (Turner syndrome).
The advent of genetic carrier screening provides women and couples further information in the pre-pregnancy and early pregnancy period. This can be confusing for women and couples and compound the feeling of being overwhelmed prior to conceiving, commencing IVF treatment or when pregnant.
I offer genetic screening – but you may ask why do it?
The goal of pre-pregnancy screeningis to let women and couples know if they at increased risk of having a child with a common genetic condition that will have an impact on their child/children. If a carrier status is confirmed then some couples may choose to undergo an invasive diagnostic procedure during pregnancy to determine whether their baby is affected. Being informed about their baby’s positive carrier status may prepare women and couples for the future or in some cases they may make the heart breaking decision to terminate the pregnancy.
Prior to commencing IVF treatment genetic screening also allows women and couples to determine whether they wish to have the embryos screened so that an embryo is transferred without the affected gene; a procedure known aspreimplantation genetic diagnosis (PGD). Others still may choose to utilise donor sperm or find a suitable egg donor.
In pregnancy the test is done so that women are better informed about their pregnancy.
There are no strict guidelines. Certainly if there is a family history of a genetically linked condition then the woman +/- male partner/donor should be screened. However with no family history many couples are offered genetic screening especially when they are seeking fertility treatment. It must be pointed out that for some women and couples the knowledge gives them important information about future pregnancies and aids in decision making, while for others it provokes prolonged and significant anxiety.
Screening can be done for couples with a family history of a specific genetic condition or in a population of people where genetic disorders are common e.g. Ashkenazi Jewish people. For other people with no specific indication there are three commercially available genetic screening tests that I will discuss with you.
These included Cystic Fibrosis (CF), Fragile X (FX) and Spinal Muscular Atrophy (SMA). Many people are carriers of CF, FX or SMA even though they do not have anybody in their family who has the condition.
Screening tests can detect 90% of people who are carriers of CF, 95% of people who are carriers of SMA and over 99% of people who are carriers of FX. It’s important to note that the test is not 100% accurate.
In the Caucasian population 1 in 25 people are carriers. If two carriers are trying to conceive they have a 1 in 4 chance of having a child with Cystic Fibrosis. Modern medicine has dramatically improved the life expectancy for children born with CF. However many still suffer from severe respiratory infections from childhood requiring hospital admissions, regular antibiotics and chest physiotherapy and have problems with malnutrition and pancreatic disorders. The genetic deletion causes a thickening of secretions in the lung and digestive symptoms.
FX is caused by an increase in the length of the FMR1 gene. 1 in 150 people are carriers of the FX gene. The FX carrier test will tell women whether they carry the low risk gene or the increased risk gene. Women who carry the increased risk gene may have a child with FX, regardless of their male partner/donors status. A male baby born with FXS is at increased risk of cognitive impairment, behavioural issues, disorders of the nervous system, autism and epilepsy. Females may have premature ovarian failure and find it difficult to conceive. Unfortunately there is no cure for FX.
SMA is a condition that affects nerves in the spinal cord and causes muscles to get weak. This not only affectsthe muscles for movement but also the respiratory muscles. There are several types of SMA with Type 1 being the most severe. Like Cystic Fibrosis both the female and male partner/donor need to be carriers for a child to be effected. Should two carriers meet they have a 1 in 4 (25%) chance of having a child born with SMA. In the general population 1 in 70 people are carriers of SMA.
I will offer you genetic counselling so that you can make an informed decision regarding your current or future pregnancies. You may choose to continue trying to conceive and do nothing, undertake further tests on your baby or undertake IVF and preimplantation genetic screening.
You may wish to provide this useful information to relatives so they could also be screened.
I often tell patients these screening tests are useful only if you wish to act on the results or be better informed about your pregnancy. If this something you don’t require prior to pregnancy then you don’t need to do anything.