Aspects of counseling

The probability with which a positive (abnormal) result of a Harmony^® Test can be confirmed depends on two factors:

1. the false positive rate of the test for this chromosomal disorder
2. the frequency of the occurrence of this chromosomal disorder in the base population

The Harmony^® Test has a very low false positive rate compared to other NIPT methods, for example, the false positive rate for trisomy 21 is approx. 1:2500 (0.04%, data from the Stokowski-Study¹). The false positive rates for trisomies 13 and 18 are even lower.

Based on this very low false positive rate (FPR), the Harmony^® Test has a particularly high positive prediction value (PPV). The FPR reflects the percentage of false positive results found in the overall collective of performed tests. The PPV reflects the rate of positive test results that are confirmed by standard chromosome analysis.

By comparison: the PPV of first trimester screening is approximately 5 – 7 %. This means that only 1 out of 18 abnormal results is confirmed by an invasive diagnosis; in 17 out of 18 cases, standard first trimester screening leads to an unnecessary invasive intervention with the risk of a miscarriage.

A typical cause of a false positive result in a NIPT is a discordance between the cells of the placenta and those of the child. Since the cell-free fetal DNA comes from the placenta, the Harmony^® Test basically reflects the genetic situation in the placenta. In some cases, however, the genetic makeup of the unborn child differs from that of the placenta. This means, for example, that some of the cells in the placenta display a trisomy and others do not (mosaic). In these cases the Harmony^® Test may show a high risk for a trisomy even though the child has normal chromosomes.

Another reason for a false positive result is if a pregnancy had started out as a twin or multiple pregnancy. If a deceased fetus suffered from a chromosomal disorder, this could lead to a false positive result of the Harmony^® Test; the placental material of the deceased fetus may still exist in the womb at the time of blood sampling, allowing cell-free DNA from that fetus to be released into the maternal blood.

The rates for false positive and false negative results in the Harmony^® Test are lower than with other non-invasive tests that are based on the detection of free fetal DNA in the mother’s blood.

The false positive rate of the Harmony^® Test for monosomy X (45,X0) is approximately 0.8%, which is higher than the other chromosomal disorders. NIPT may show false positive X0 results due to the age-related loss of the second X-chromosome in the mother’s own cells (X-chromosomal loss, XCL). According to Russell LM et al.,² a 40 year old woman may have, on average, approximately 2% XCL cells. If the fetal Fraction (proportion of fetal DNA in the maternal blood) is also relatively low (e.g. 4%), the NIPT may produce a result of a fetal monosomy X (Turner Syndrome). This is because it would appear that 50% of the X-chromosomal information of the fetus is missing, when in fact it is simply a higher rate of XCL in the mother that is causing the false result. Thus with advanced maternal age and a low proportion of fetal DNA in the maternal blood, there may be a higher false positive rate for fetal monosomy X (Turner syndrome); this should be discussed with the patient during the consultation if they wish an analysis of the XY-chromosomal disorders.

In cooperation with Prof. Oliver Kagan (University Hospital Tübingen) and Francesca Grati (TOMA Advanced Biomedical Assays S.p.A.), we determined the positive predictive value (PPV) in screening for gonosomal aneuploidy (SCA) using NIPT. 

The most important results of the study:

• At 38.9% the PPV of an abnormal cfDNA result in gonosomal aneuploidy is lower than in trisomy 21, 18 or 13. In monosomy X in particular, only a good quarter of the abnormal NIPT results are confirmed (PPV= 26.1%).
• Amniocentesis with subsequent chromosome analysis is the method of choice for clarifying an increased risk of SCA (sex chromosomal aneuploidy) in NIPT.

“Confirmation rate of cell free DNA screening for sex chromosomal abnormalities according to the method of confirmatory testing“. This Publication was awarded as a “Top Cited Article 2021-2022” in Prenatal Diagnosis.

The Harmony^® Test offers the possibility of determining the probable sex of the fetus. The patient may only be informed of this after the 12th week of pregnancy in accordance with the Genetic Diagnostics Act (post-conception, corresponding to week 14+0 of the pregnancy after the last period). If the patient is not yet in week 14+0 of the pregnancy when the results are ready, we will send the requesting physician partial findings that do not include the sex of the fetus. When week 14+0 of the pregnancy is reached we will automatically send you the report on the sex of the fetus.

In a few cases it is not possible to obtain results with the Harmony^® Test, most often because the fetal fraction is below the 4% limit. Less common reasons for test failure include egg donation about which the laboratory was not made aware, chromosomal mosaicism of the mother or placenta, situations in which a twin fetus has died, tumour disorders of the mother, or other undefinable biological causes.

In approximately half of the tests that cannot be evaluated at the first attempt, the Harmony^® Test can be carried out at a later point in time by taking another blood sample.

Patients will not be charged any costs if no result can be obtained.

In accordance with the German Genetic Diagnostics Act, genetic counseling must be provided by either a specialist in human genetics or a specialist with an additional qualification in “professional genetic counseling” before any non-invasive prenatal test. The additional qualification for professional genetic counseling for the Harmony^® Test is taught in 72 training units and the corresponding practical-communicative qualification course (Genetic Counselling Guideline, section VII.3.4.). An interim arrangement applies until 10.7.2016.

During genetic counseling, compliance is required with the regulations of § 10 of the Genetic Diagnostics Act. Regulations must also be followed in accordance with § 2a of the German law on conflicts in pregnancies (SchKG), including informing the expectant mother of her right to psychosocial counseling. Upon request, the expectant mother should be referred to a counseling centre as directed by § 3 of the SchKG.

In accordance with the German Genetic Diagnostics Act, the responsible medical person remains the main contact partner for the pregnant woman during the entire performance phase of the Harmony^® Test. The results will be sent only to the responsible medical person.

Cenata assumes liability for any errors for which it can be held responsible in connection with the performance of the Harmony^® Test. Cenata naturally assumes no liability for errors that occur in the submitting process, for example, during the drawing of the blood samples or during shipping.

The Harmony^® Test is very easy to integrate into standard first trimester screening. As was shown by Prof. Nicolaides in an article published in July 2013, the Harmony^® Test can greatly improve the efficiency of first trimester screening:

If a trisomy 21 risk score of 1:3000 (instead of 1:300, for example) is selected for further screening, the average trisomy 21 detection rate increases from approximately 89% to the percentage detection rates shown in Figure 1 ⁵:

By lowering the risk score to 1:3000, the number of cases requiring further testing (invasive methods) would normally rise steeply. However, if the highly-specific Harmony^® Test (false positive rate 0.04%⁶) is performed in place of an invasive diagnosis, the number of invasive tests that ultimately have to be performed can be greatly reduced overall.