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Yes, Non-Invasive Prenatal Testing can be done in a twin pregnancy, and it is the most accurate screening test available for Down syndrome in twins. Major professional bodies, including the American College of Obstetricians and Gynecologists and the International Society for Prenatal Diagnosis, recognize it as an option for screening twin pregnancies for the common chromosome conditions.
How the test works
Non-Invasive Prenatal Testing is a simple blood test taken from the mother, usually from about 10 weeks of pregnancy. It looks at small fragments of DNA floating in the mother’s blood. Some of these fragments come from the placenta, which usually reflects the baby’s DNA. The test checks whether there is too much or too little DNA from a particular chromosome.
How accurate it is in twins
For Down syndrome (trisomy 21), a pooled analysis of twin studies found the test picked up about 98 percent of affected pregnancies, with very few false alarms. This is close to its performance in single pregnancies.
For Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13), there is much less information in twins, because these conditions are rare and fewer twin cases have been studied.What it cannot tell you
This is where twins differ most from single pregnancies:
It usually cannot say which baby is affected. In non-identical twins, a high-risk result means one baby or both may be affected. Only a diagnostic test of each baby can answer that.
Not every test method can tell identical from non-identical twins. Some laboratory methods can estimate this. Others give one combined result for the whole pregnancy.
Some conditions are not reliably screened in twins. Screening for small missing pieces of chromosomes (microdeletions) and for sex chromosome conditions is generally less reliable, or not offered, in twin pregnancies.
It does not check how the babies are developing physically. Problems such as spina bifida or heart defects are picked up on scans, not on this blood test.Why some twin tests come back with “no result”
The test needs enough placental DNA in the mother’s blood. This is called the fetal fraction. In non-identical twins, each baby contributes only part of the total. One baby’s share can be too low to analyze reliably, even when the overall amount looks fine.
For this reason, “no result” reports are more common in twins. A no-result report does not mean something is wrong. Often, a repeat blood sample a little later in pregnancy solves the problem, and Team Genetidoc offers a repeat sample when the fetal fraction is too low.
Other practical points
Results are usually available in about two weeks.
Genetidoc does not report the sex of the babies, in line with India’s Pre-Conception and Pre-Natal Diagnostic Techniques Act, 1994.
A low-risk result greatly lowers the chance of the conditions tested, but it is not a guarantee of healthy babies. Your regular pregnancy scans remain essential.Genetic counseling before the test helps you understand what a result can and cannot tell you about each baby, so that a report never comes as a shock.
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