RCSI Women's Health

How to choose between various screening tests:

It can sometimes be quite difficult to figure out which of the wide range of prenatal tests to choose. It is often easiest to approach this decision in three easy steps:

STEP 1: Should I look for prenatal test results at all?

The first question that all patients and their partners should answer is "Do I want this information at all"? Finding out prenatally whether your baby is healthy or has a problem is a complicated issue and is completely voluntary. It is important to realise that you do not need to undergo any of these tests, irrespective of your age or medical background. Reasons that are commonly quoted by patients to get this information include:

  • "I do not want to wait until the end of the pregnancy to find out if my baby is healthy"
  • "If I find out early in pregnancy that my baby has a serious medical problem then I can prepare myself and my family by getting as much information as possible"
  • "If I find out that my baby has a serious medical problem I can make arrangements to meet with the relevant paediatric specialists in advance and, if necessary, make arrangements to deliver my baby at a special time or in a special location to improve the chances that my baby will do well"
  • "If I find out that my baby has such a serious abnormality that the baby will likely not survive, I could avoid having a caesarean section, or avoid delivering far away from my family or my home"
  • "If the tests prove that my baby has a serious abnormality, I can have time to figure out what the full implications of this are, and if I want to, I can choose to travel outside of Ireland to obtain a pregnancy termination"

A key concept in the areas of fetal medicine and prenatal diagnosis is "non-directive counseling". This means that you should be able to choose whether or not to have any prenatal tests that you wish, and once you receive results, you should be provided with information on all options available to you, in a non-judgemental manner. Only you, with your partner or family, can make the right decision on what to do with such information.

STEP 2: Should I have a screening or a diagnostic test?

CVS (chorionic villus sampling) and amniocentesis are examples of diagnostic tests for conditions like Down syndrome. That means they can tell you for sure whether the baby either has, or does not have, such a condition. Some patients prefer to get very definite, or "black and white" information, like this. However, since these tests involve placing a thin needle into your uterus, there is a small risk that a miscarriage might be triggered. This chance may be about 0.5% to 1%, or about one in 100 to one in 200.

Because of the concern about possibly triggering a miscarriage, some patients prefer to avoid these needle tests, unless absolutely necessary. In this situation, a screening test that gives a more accurate assessment of the chances of a problem with the baby may be suitable. Screening tests do not tell you whether the baby is healthy or whether the baby has a problem. Instead, they tell you what are the "odds" or chances of this happening. If the screening test result suggests that the "odds" of a problem are high, then you can have the definitive diagnostic test at that time.

STEP 3: How far along in my pregnancy am I?

Different diagnostic tests and different screening tests are available depending on how far along in pregnancy you are. To figure out how far along you are in your pregnancy, and to find out which of these tests may be available for you, please enter your pregnancy dating information in the box below. If you know the date of the first day of your last menstrual period, enter that date in the correct box below. Alternatively, if you don't know this date, but you do know your expected due date, enter that date in the correct box below. Information will then appear suggesting how far along in pregnancy you are, and when various tests should be scheduled.

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