At the first antenatal visit or as early as possible in pregnancy, the availability of screening for chromosomal abnormalities should be discussed and women given relevant written information or other appropriate materials (eg video, DVD) (see Section 9.5). Providing information is particularly important, due to the complexity of the screening process and the level of decision-making that may be required. A systematic review found that levels of knowledge adequate for decision-making were at times not being achieved despite information leaflets and video having some effect (Green et al 2004). Studies in which knowledge about genetic screening is increased have not observed a corresponding increase in anxiety (Green et al 2004).
In discussing screening tests, it is important to explain:
- that it is the woman’s decision whether any testing takes place;
- the chromosomal abnormalities for which screening is available;
- the screening pathway, the decisions that need to be made at each point and their consequences (see Figure 9.1);
- the importance of timing the tests against an accurate assessment of gestational age;
- that a screening test alone indicates a risk but does not give a diagnosis of any abnormalities;
- the sensitivity and specificity of the test and a full explanation of the risk score obtained following testing (eg high risk/low risk, 1 in 300);
- the options for women who receive a high-risk result, including information about chorionic villus sampling and amniocentesis (see Section 9.3.2);
- a high risk screen in a fetus with normal chromosomes may indicate the presence of other fetal anomalies (diaphragmatic hernia, cardiac anomaly);
- factors that increase the risk of fetal chromosomal abnormalities (advanced maternal age, family history of chromosomal abnormalities);
- where and how tests can be accessed if the woman chooses to have them;
- situations in which first-trimester screening may be difficult or impossible (eg high BMI, fetal positioning, multiple pregnancy);
- situations in which the testing may be modified to exclude serum testing (multiple pregnancy);
- the availability of evaluated decision aids (eg the Ottawa Decision Framework) (Arimori 2006; Nagle et al 2006; 2008)(see Section 9.5); and
- the costs involved for the woman and the timeframe for receiving results.
Consensus-based recommendationix. At the first antenatal visit, give all women information about the purpose and implications of testing for chromosomal abnormalities to enable them to make informed choices about whether or not to have the tests.
Practice pointu. Information about testing for chromosomal abnormalities should be provided in a way that is appropriate and accessible to the individual woman, with particular regard given to language and literacy.
Figure 9.1: Pathway of screening for and diagnosis of chromosomal abnormalities in the first trimester (in the accessible text format)
Step 1: Women offered screening for chromosomal abnormalities
Purpose: Identify women who may be at risk of having a baby with a chromosomal abnormality Offer counselling from informed professional eg ultrasound specialist/obstetrician/midwife/GP/geneticist
Women may choose or may not choose to have screening test, If Women chooses to have screening test go to Step 2
Step 2 : Screening test: nuchal translucency ultrasound + blood test. Screening test will show either there is High Risk or Low Risk
Step 3 : If Results shows Increased risk (1 in 300 or greater) Go to Step 4
Step 4 : Woman is offered referral to a genetic counsellor
Step 5 : Women with a high-risk screening result offered diagnostic test
Purpose: To enable the woman to have further testing to make an informed decision about the pregnancy
Woman may choose or may not choose to have diagnostic test
Step 6 : Woman chooses to have diagnostic test
Step 7 : Diagnostic test: chorionic villus sampling at >11 wks, amniocentesis at >15 wks
Test result may be Negative or Positive
Step 8 : If Diagnostic test results are Positive, Woman is offered counselling and preparations are made for additional care required during and after the pregnancy or for termination*
* The circumstances in which termination of pregnancy is permissible vary between States/Territories. Health professionals should be aware of relevant legislation in their State/Territory.