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Prenatal screening guide · 2026
NIPT works in twins and in IVF pregnancies, with caveats specific enough that the laboratory needs to know before it runs the sample.
NIPT can be used in twin pregnancies, but performance is lower than in singletons: the fetal fraction is shared, so the contribution from each fetus is smaller, and test failure rates are higher. It cannot usually tell you which twin is affected. A vanishing twin is a recognised cause of false positive results and can persist for weeks. In IVF, donor egg and surrogate pregnancies NIPT works normally, because the cell-free DNA comes from the placenta rather than from the person carrying the pregnancy — but the laboratory must be told, since it affects interpretation of some results.
| Twins | Usable, with lower performance and higher failure rates than singletons |
|---|---|
| Cannot identify | Which twin is affected in a dichorionic twin pregnancy |
| Vanishing twin | A recognised cause of false positives; disclose it |
| IVF and donor eggs | NIPT works normally — the DNA is placental, not maternal |
| Always tell the laboratory | Number of fetuses, IVF, donor gametes, surrogacy, vanishing twin |
| Counselling | Doctor consultation or specialist teleconsultation before and after testing |
In a twin pregnancy the total fetal fraction is shared between two placentas, so each contributes less than a singleton would. Since the test depends on detecting a difference against a background, a smaller contribution makes detection harder.
The practical consequences:
Monochorionic twins, being genetically identical, are more straightforward to interpret. Chorionicity is determined by ultrasound in the first trimester, which is another reason for a scan before testing — see MedEx imaging services.
A vanishing twin is a twin that stops developing early in pregnancy. It is more common than most people realise, particularly after IVF, and often the only evidence is an early scan showing two sacs where a later scan shows one.
DNA from the twin that stopped developing can persist in the maternal circulation for weeks. If that twin had a chromosomal abnormality — which is a common reason for early loss — NIPT may detect it and report a high-risk result for a pregnancy that is entirely unaffected. It can equally produce a discordant fetal sex result.
This is why early scan history matters. Tell the laboratory if two sacs were ever seen, even briefly. Without that information, an unexplained result may lead to an invasive procedure that was avoidable.
Twins or IVF? Tell us at booking — it changes how the sample is interpreted.
A frequent misunderstanding is that NIPT cannot work with donor eggs because the DNA is not the carrier’s. In fact the opposite is true: the cell-free DNA being analysed comes from the placenta, which is derived from the pregnancy itself. So NIPT works in donor egg, donor sperm and surrogate pregnancies.
What does need declaring:
| IVF | Gestational dating is usually precise, which helps timing. Vanishing twin is more common, so early scan history matters. |
|---|---|
| Donor eggs | Some laboratory algorithms use maternal genotype information; declaring donor gametes ensures correct interpretation. |
| Surrogacy | Same principle. The laboratory needs to know whose sample it is and whose genetics are involved. |
| Prior PGT-A | Preimplantation genetic testing does not remove the value of NIPT, since PGT-A is itself subject to mosaicism and error. Discuss both results together. |
That last row comes up often. An embryo screened as euploid still warrants prenatal screening, and the two tests are not interchangeable. Discuss through a specialist teleconsultation or with MedEx genetic testing services.
Book through the MedEx NIPT service and mention the pregnancy details when you do.
Yes, but performance is lower than in singletons because the fetal fraction is shared, and failure rates are higher. Evidence in twins is also less extensive.
Not in a dichorionic twin pregnancy, where the twins are genetically distinct. Localising a finding requires ultrasound and, if needed, diagnostic testing of each amniotic sac.
Yes. The cell-free DNA analysed comes from the placenta, which is derived from the pregnancy itself, not from the person carrying it. Tell the laboratory, since some algorithms use maternal genotype information.
DNA from a twin that stopped developing early can persist for weeks and may produce a false positive result or a discordant fetal sex result. Tell the laboratory if two sacs were ever seen on an early scan.
Preimplantation genetic testing does not remove the value of prenatal screening, since PGT-A is itself subject to mosaicism and error. The two tests are not interchangeable and results should be discussed together.
Yes. Because the fetal fraction is shared between two placentas, more twin samples return a non-reportable result and require a repeat draw.
Chorionicity is established by ultrasound, ideally before testing.
Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.
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