Frequently asked questions
Only you can make the decision about whether or not to have screening. Some women want to know about possible conditions and some do not. Your midwife or doctor can provide you with information both directly and from pamphlets, websites and other organisations to help you make your decision.
You may like to contact organisations which provide support for families who have children with disabilities or conditions for example. These organisations may also be able to help you with your decision.
It is important to make sure you have fully considered whether screening is right for you, so make sure you discuss it carefully with your midwife or doctor and your family if you wish.
Whether or not you choose to have screening, you will be supported in your decision.
View the useful links page for organisations which may be able to help you.
The main difference between screening tests and diagnostic tests is that screening is only meant to find out whether there is a higher chance that your baby has a condition or a lower chance, whereas diagnostic testing is designed to find out for sure whether or not a baby has a condition.
Although you can get a more definite result from diagnostic testing, there is a risk of misscariage each time a genetic diagnostic test is done. If everyone has screening first only those found to have a higher chance of carrying a baby with a condition are offered diagnostic testing. This should mean fewer babies have a diagnostic test and therefore fewer misscarriages because of them.
Ideally you should have screening during the first three months of your pregnancy. If you do plan to have screening and are under 14 weeks pregnant you will be offered First Trimester Combined Screening.
First trimester combined screening includes both a blood test and an ultrasound scan. The blood test is best taken at 10 weeks but can be taken any time between 9 weeks and 13 weeks and 6 days. The ultrasound scan (called a nuchal translucency), is best done at 12 weeks of pregnancy but can be done any time between 11 weeks and 2 days and 13 weeks and 6 days of pregnancy.
If you are 14 weeks pregnant or more when you decide to have screening, you will be offered Second Trimester Maternal Serum Screening. This is a blood test which is best taken between 14 and 18 weeks of pregnancy but can be taken up until 20 weeks.
Both types of screening include a blood test which measures the levels of certain hormones and proteins (chemicals) in your blood. The levels of these tend to be either higher or lower when you are carrying a baby with Down syndrome or some other conditions.
In the case of first trimester combined screening, an ultrasound scan is also carried out. It is called a nuchal translucency scan and measures the thickness of the nuchal fold which is a fluid filled space at the base of the babies neck. The nuchal fold tends to be thicker in babies with Down syndrome and some other conditions.
Studies have shown that when these measurements are combined with information about your age, weight and how far along in your pregnancy you are, the differences between them and what is most commonly seen in women who have had these tests in the past can be compared. A computer programme works out what the chances are that your baby will have one of the conditions which can be identified by screening and comes up with a low or increased risk result.
Your doctor or midwife will give you your result. They will tell you whether the result shows that there is a low or increased chance that your baby has a condition. You will be given your screening results within 10 days of finishing screening.
Your results sheet will say either 'Increased Risk' or 'Low Risk'
- Low Risk - this result means that you have a low chance of having a baby with one of the conditions being screened for.
- Increased Risk - this result means that there is an increased chance that you are carrying a baby with Down syndrome or another condition
In New Zealand we choose to make the cut-off for screening at 1 out of 300. An example of "increased risk" is 1 out of 200. An example of "low risk" is 1 out of 500.
It is really important to remember that screening only measures the chances of your baby having a condition. Most women in the increased risk group will find out that their babies do not have a condition either when they have diagnostic testing or when their baby is born.
If your results show an increased chance discuss what your choices might be with your doctor or midwife. They will be able to give you some information as well as helping you to find other organisations and people who can help. Sometimes talking to organisations which deal with helping families to manage children with condtions like Down syndrome can help with your decision making. Your doctor or midwife will offer to refer you to a specialist obstetrician to further discuss your options for diagnostic testing.
Only you can decide if diagnostic testing is the right choice for you. Some women choose to stop at this point regardless of an increased risk result while others want to have diagnostic testing so that they can find out for sure whether their baby has one of the conditions being screened for.
Diagnostic genetic testing
Diagnostic testing can be genetic testing. This will be either chorionic villus sampling or amniocentesis. In most cases amniocentesis is the genetic diagnostic test offered. During these tests, samples are taken either from the fluid around baby (amniocentesis) or the developing placenta/whenua (CVS). These samples are sent to the laboratory where baby's cells are found, grown and examined so as to see if they have the expected chromosome numbers and shapes. Only this type of testing can confirm whether or not your baby has one of the genetic conditions able to be seen, before he or she is born.
What can it pick up?
Remember that this type of testing only picks up genetic conditions which can be seen in chromosomes under a microscope. These are conditions like Down syndrome, Trisomy 13, Trisomy 18 and Turner syndrome. It is possible that even though baby does not have one of these conditions there might be some other condition present when baby is born.
Risks of diagnostic testing
It is also important to remember that amniocentesis and choronic villus sampling have some risks. Between 1-2 percent of babies miscarry because of the genetic test. When making your decision talk to your specialist Obstetrician about the limitations of diagnostic testing and the risks before making your decision.
Other forms of diagnostic testing
Diagnostic testing in some cases is diagnostic ultrasound. This might be the case when the condition for which the increased risk result was made was spina bifida or a heart condition for example. In some of these cases both a diagnostic scan and a genetic test might be offered.