NIPT (Non-Invasive Prenatal Test): Ultrasound Scan and Blood Test

No – you cannot have a NIPT test if you

• are carrying more than two babies
• currently have active malignant cancer
• are currently undergoing radiotherapy or chemotherapy
• are carrying a pregnancy with fetal demise or vanishing twin
• have a history of organ transplant
• have mosaicism or maternal aneuploidy, which are rare maternal biological conditions
• have a maternal autoimmune disease
• have received a blood transfusion in the last 12 months
• have partial chromosome aneuploidy (a genetic disorder)
• have triploidy (a rare chromosomal abnormality)

The Warwick Evidence Systematic Review of the performance of NIPT found that the negative predictive value (NPV) of NIPT was 99.9%. The NPV tells you how likely it is that a low probability NIPT result is correct. This means that if you get a result that shows a low probability of the chromosomal conditions you can be fairly certain you do not have a fetus with any of the conditions.

The positive predictive value (PPV), which shows how likely it is that a high probably NIPT result is correct, varies for each condition tested:

• 82% for Down’s Syndrome (known as Trisomy 21)
• 49% for Patau’s Syndrome (known as Trisomy 13)
• 37% for Edwards' Syndrome (known as Trisomy 18)

A high probability result does not definitively confirm the presence of one of the conditions and further testing is required.

The NIPT test will detect 99% of pregnancies where a high probability of Down's Syndrome, Edward’s Syndrome or Patau’s Syndrome is present.

Results can also be inconclusive, which happens in less than 1% of cases. This is usually because the proportion of fetal DNA present in the sample is not high enough to give an accurate result. The test may be repeated with the hope that the fetal DNA levels will have increased due to the increased gestation. In some rare cases however, the fetal DNA is naturally low and in these instances a result cannot be yielded.

The NIPT is more accurate than the first trimester combined test or second trimester quadruple test for estimating the chance that the baby has Down's Syndrome. The combined false positive rates are 0.13% for Downs Syndrome, Edwards' Syndrome and 0.01% and Patau's Syndrome. Conventional screening tests can miss 15% or more of Down’s Syndrome pregnancies.

cfDNA is short for ‘circulating free DNA’. Fetal cfDNA is the circulating free DNA from your fetus in a maternal blood sample. The proportion of cfDNA in maternal blood that comes from the placenta is known as the fetal fraction.

The fetal fraction must be above 1.4%, which typically occurs around the tenth week of pregnancy. Low fetal fractions can mean the NIPT test can’t be done, or create a false negative result. Reasons for low fetal fractions include testing too early in the pregnancy, sampling errors, maternal obesity, and fetal abnormality.

An ultrasound Nuchal Translucency (NT) measurement (which measures the thickness of the fluid at the back of the baby's neck) when combined with a blood test and other maternal information provides an indication of the likelihood of a baby being born with Down’s Syndrome.

NIPT directly analyses the cell-free fetal DNA circulating in the pregnant mother's blood to detect the presence (or absence) of Down’s Syndrome, Edward’s Syndrome and Patau’s Syndrome.

The detection rate for NIPT is among the highest available for this type of antenatal screening and is recommended by the International Society of Prenatal Diagnosis (ISPD).

Yes, but not for triplets or higher multiple pregnancies. If one of the fetuses is no longer viable, the Harmony NIPT test cannot be performed.

We’ll take a new sample at no extra cost. There is a 0.2% failure rate for the overall test.

On rare occasions, NIPT is unable to provide an assessment of the probability of specific chromosome disorders. This usually reflects the complex biology of genetics and pregnancy, and is not due to a failing in the laboratory.

If NIPT cannot provide a specific assessment, it is not worth repeating the NIPT (unless advised by the laboratory). A decision about other tests (maternal serum screening, detailed ultrasound, amniocentesis or CVS) should be based on the doctor’s assessment of all risk factors identified, and may require specialist consultation with your doctor.

Yes, because with increasing body weight there is an increasing probability that there will be insufficient cell-free fetal DNA to provide a reliable result. On average, women who weigh 140kg will have a fetal fraction rate that is approximately half that of a woman weighing 70kg. This may increase the chance of getting an inconclusive result.

No, we do not offer this. A microdeletion is the absence of a small piece of chromosome and is named by the area of the chromosome that is absent. Due to a lack of research into the reliability of this test, we do not offer it.

This test has a 0.13% false positive rate. Results should always be confirmed by amniocentesis or Chorionic Villus Sampling (CVS) before making any decisions regarding subsequent management of your pregnancy. We always recommend you discuss your results with your Midwife or Consultant.

We do not offer this type of screening to evaluate the X and Y chromosomes. This is due to a lack of research currently available into the accuracy and detection rates of this test.

Absolutely! Every scan at Ultrasound Direct is performed by a fully qualified sonographer whose primary interest is your health. All our sonographers are fully trained and appropriately qualified to perform ultrasound scans. Many of our team also work in the NHS locally.

All our sonographers are registered with the Health and Care Professions Council and/or the Register of Clinical Technologists and follow the latest safety guidelines.

We are also registered with the Care Quality Commission, an independent regulator, to make sure you always receive the highest possible standards of care. 

All our sonographers who take blood for blood tests are phlebotomy trained.

If you are experiencing pain or bleeding, go directly to your local A&E or contact your midwife – do not book an ultrasound scan. This is because you may be experiencing a medical emergency and waiting for a scan will cause a potentially harmful delay.

Research suggests that there are no known risks to our method of ultrasound scanning. Scans are painless (although an internal scan may be slightly uncomfortable) and have no known side effects. Ultrasound scans do not use any form of ionising radiation, unlike other diagnostic imaging services such as x-rays.

 We follow the British Medical Ultrasound Society’s guidance for the safe use of diagnostic ultrasound equipment.

 During pregnancy scans, we can record your baby’s pulsebeat – this sounds very similar to the heartbeat, but is recorded in a different way. We record the pulsebeat by scanning blood flow through the umbilical cord, rather than recording the heartbeat by scanning the heart. This is because consistent ultrasound output in one place can have a heating effect, and we don’t want to put your baby at any level of risk. The fast-moving blood in the umbilical cord quickly disperses any potential heating effect.

Visit our FAQs page for any further questions you may have.