NIPT With Twins

What NIPT is used for on the NHS

Non-invasive prenatal testing uses placental DNA circulating in the mother's blood to assess the chance of a baby having Down's syndrome, Edwards' syndrome or Patau's syndrome. The NHS FASP handbook is precise about its place in the pathway: NIPT screening is offered following a higher-chance result, between 1 in 2 and 1 in 150, from either the NHS combined or the quadruple test. It is not the first test, and on the NHS it is not a test you choose instead of the combined test.

The handbook is equally clear about scope. As part of the NHS FASP care pathway, NIPT screens for those three conditions only. It does not screen for other chromosomal conditions and does not assess the baby's sex.

Twins: yes, with the same trigger

The FASP handbook states that NIPT can be offered and performed in both singleton and twin pregnancies. The route in is identical: a higher-chance result from the combined or quadruple test first. So if you are carrying twins and your combined test result falls between 1 in 2 and 1 in 150, NIPT is on the table.

What a higher-chance NIPT result means with twins

This is the part that is genuinely different, and it is worth reading twice. The handbook says that in twin pregnancies, a higher-chance NIPT result report should state that one or both babies may have the condition screened for. The test does not tell you which baby.

The handbook also requires the NIPT result report to record whether the pregnancy is singleton or twin, and to include chorionicity in a twin pregnancy, stating monochorionic, dichorionic or unknown. Chorionicity is on the form because it changes how the result is interpreted.

Triplets and more: not offered

The FASP handbook lists the circumstances in which NIPT cannot be offered and performed, and higher multiple pregnancies, triplets or more, are on that list. It also says elsewhere that NHS FASP screening for these three conditions is only available for singleton and twin pregnancies at all, and points to NICE for higher multiples.

NICE NG137 fills that gap with a different approach. For trichorionic triplet pregnancies it says healthcare professionals should map the fetal positions, use nuchal translucency and maternal age to screen, and calculate the chance for each fetus. For dichorionic and monochorionic triplet pregnancies it says women who want screening should be referred to a tertiary level fetal medicine centre. It also says second trimester serum screening should not be used for Down's syndrome in triplet pregnancies.

Vanished twin: ruled out, and for a specific reason

The handbook says NIPT cannot be offered in a vanished twin pregnancy, meaning an empty second pregnancy sac or a second sac containing a non-viable fetus. The reason it gives is that there is evidence to suggest the placenta can continue to shed cell-free fetal DNA even after the baby has died, which would contaminate the result.

This is one of the few situations where a pregnancy that looks like a singleton on the screen is handled entirely differently because of what an earlier scan showed. It is why the dating scan findings have to be recorded accurately.

Other situations that need a call to the laboratory

The handbook lists circumstances where the laboratory must be contacted before a NIPT sample is taken, including a cancer diagnosis in the current pregnancy, certain immunotherapy treatments, and a known chromosomal condition other than the three being screened for. It also flags stem cell therapy as a complication, because some NIPT methods are unsuitable afterwards. None of these are twin-specific, but they apply to twin pregnancies too.

Why chorionicity is on the request form

The FASP handbook requires the NIPT screening result report to state whether the pregnancy is singleton or twin, and for a twin pregnancy to record chorionicity as monochorionic, dichorionic or unknown. That mirrors how the combined test is reported: the handbook says that in a monochorionic twin pregnancy one pregnancy chance result is given because the babies share the same genetic material, while in a dichorionic twin pregnancy a chance result is reported for each baby.

NICE NG137 is the reason chorionicity is known at all. It asks for it to be determined at the scan when the twin pregnancy is detected, and says that where it cannot be established even after referral, the pregnancy should be managed as monochorionic until proven otherwise. If your notes say unknown, that is the entry to query.

Private NIPT with twins

Private providers set their own rules, and we are not going to characterise them collectively. What the NHS handbook does establish is the standard the NHS pathway holds itself to: a defined trigger, a defined set of three conditions, defined reporting requirements including chorionicity, and defined exclusions. Those are reasonable questions to put to any provider before paying.

What NIPT is not

It remains a screening test. The NHS says a higher-chance screening result leads to a discussion about diagnostic testing, and the FASP handbook confirms that chorionic villus sampling and amniocentesis are the diagnostic options in twin pregnancies. It also records that the risk of miscarriage from those procedures is twice as high in twin pregnancies as in singleton pregnancies, and that they should be performed at a tertiary-level fetal medicine unit because of the specialised nature of the procedure and the increased risk.

None of which is a reason not to have NIPT. It is a reason to know, before the blood is taken, what each possible result would actually lead to.