Screening versus diagnostic tests: Two Different Ways to Assess Risk

Screening and diagnostic tests answer different questions during pregnancy. Screening estimates whether a condition is more or less likely. Diagnostic testing can establish whether particular conditions are present, depending on the test ordered. Neither phrase means that every possible health condition has been assessed.

Start with the question being asked

A combined screening result or NIPT result describes chance. A higher chance result can be followed by diagnostic testing, but you can also choose not to have more tests. A lower chance result cannot guarantee that a baby has none of the conditions screened for.

Ask the clinician to finish this sentence: this test will help us find out whether. Then ask what it will leave unanswered. The NIPT article gives an example of a blood test that is highly informative but remains screening.

Understand the procedure behind diagnosis

Two common prenatal diagnostic procedures are chorionic villus sampling, called CVS, and amniocentesis. CVS takes a small sample from the placenta. Amniocentesis takes fluid from around the baby, which contains cells for testing. The laboratory tests selected for that sample determine which conditions can be assessed.

CVS is usually performed earlier, around 11 to 14 weeks. Amniocentesis is usually performed from 15 weeks. Your specialist explains which procedure is suitable, its timing and whether further testing might be necessary if a result is uncertain.

These procedures carry a small risk of miscarriage and other complications. Ask the service to explain the risk in your circumstances, including whether you are carrying more than one baby. The benefits and procedure risks deserve a separate discussion from the chance of the condition itself.

Compare information as well as timing

Ask when an initial result might arrive and whether a more detailed result will take longer. A quick result for selected conditions is not necessarily the final report. Check who will contact you and what happens if the sample does not provide a clear answer.

The combined screening guide explains how the earlier estimate was produced. Bring the original report, family history and scan information so the specialist can consider the whole picture.

Keep consent specific to the next step

Having screening does not mean you have already agreed to an invasive procedure. Ask about alternatives, including no further testing, and how care would continue with each option. You can request information about the condition, specialist support and what a confirmed diagnosis could mean for pregnancy and newborn care.

A useful appointment ends with a clear next step rather than a pressure to choose what someone else would choose. Write down the plan, any decision deadline and the number to call with questions after you have had time to absorb the information.