Which test should I opt for: second trimester screening or NIPT ?

[Anonymous]

Is second trimester screening still worth doing if Non-Invasive Prenatal Testing is available, and what can neither test detect?

[Genetic Counselor]

Both are valid choices. The right one depends on cost, access, timing, and what you want to know.

• Non-Invasive Prenatal Testing: This is the most accurate screening test for Down syndrome, Edwards syndrome, and Patau syndrome. It finds about 99 in every 100 babies with Down syndrome and gives far fewer false alarms than the quadruple marker test. It can be done from 10 weeks and at any time after. It is more expensive, and sometimes returns a “no result”, which needs follow-up. The Society for Maternal-Fetal Medicine does not recommend routine screening for rare microdeletions with this test, and advises that screening for sex chromosome differences should be optional.
• Quadruple marker test: This is less expensive and widely available across India. It detects fewer affected babies and gives more false alarms. Its main advantage is the alpha-fetoprotein measurement, which also screens for open neural tube defects.

Neither test can:
• Diagnose a condition. Only amniocentesis or chorionic villus sampling can confirm a result.
• Check for single-gene conditions: Beta-thalassemia, sickle cell disease, spinal muscular atrophy, and cystic fibrosis need carrier screening of the parents, ideally before or early in pregnancy.
• Replace the anatomy scan: All pregnancies should have a detailed scan at 18 to 22 weeks, whichever screening test is chosen.
A consultation with a clinical geneticist can help you decide which test fits your pregnancy best and make sense of any result you have already received.

[Author]

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