Frequently asked questions about the non-invasive prenatal test

What are the differences with the anomalies detected by an amniocentesis?

At the chromosomal level, NACE® detects anomalies in the number of chromosomes, not in their structure. It only detects anomalies for a limited number of chromosomes related with problems in gestations after the second trimester of pregnancy.

Can a NACE® test be done following a transfusion? How long do I have to wait after a transfusion to perform the test?

If the transfusion was with complete blood you should wait a minimum of six weeks after the transfusion for the NACE® test blood extraction.

If you were transfused only with red cells, these do not contain a nucleus or DNA.

In trauma interventions where a lot of blood is transfused the presence of donated leukocytes has been detected up to a year and a half later.

Can the study be done in twin gestations?

Yes, the NACE® test can be done, bearing in mind that in these cases we cannot provide information on the fetal sexes, or about any alterations in sexual chromosomes; the test only informs about the presence or the absence of a Y chromosome.

Can the test be done in gestations with twin embolization syndrome?

If the sack has disappeared the NACE® test can be indicated; however, it should be noted that DNA originating from the reabsorbed sack could remain in the maternal blood; this could result in a false positive regarding the chromosome number in the viable fetus.

If the sack remains (although it hasn’t developed) the NACE® test should not be indicated.

The probability that the sack has disappeared is very high although there is still an elevated risk that the test could produce a false positive if the other fetus had disappeared not long before performing the test, given that quite a lot of DNA from the other fetus will still remain present.

Currently there isn’t any empirical data which can confirm the percentage risk or lowest levels of sensitivity of the test in these cases – it is a possible scenario because the DNA analyzed comes from the placenta.

What happens if a NACE® test gives a positive result?

An amniocentesis or chorionic villus biopsy should be carried out. Occasionally, in cases of arrested pregnancy conventional curettage is performed. The chromosomal analysis preformed depends on the alteration found and may be:

  • Conventional karyotype: which will serve to confirm/discard complete or partial aneuploidies in any chromosome as well as results suggestive of mosaicism.
  • Quantitative fluorescent polymerase chain reaction (QF-PCR): to discard/confirm aneuploidies of chromosomes 13, 18, 21, or sexual chromosomes.
  • Fluorescent in situ hybridization (FISH) and/or short tandem repeat (STR) analysis: to discard/confirm aneuploidies of chromosomes 9 or 16.
  • FISH and/or microarray-based comparative genomic hybridization (array CGH): to discard/confirm some microdeletions.
What happens if the fetal sex result from the NACE® test isn’t the same as the ultrasound results?

A new maternal blood sample should be taken in a Streck tube and the Igenomix laboratories will determine the fetal sex (free of charge).

I’m interested

Non-invasive prenatal test