Praenatest

The PraenaTest is used for the risk-free determination of chromosomal defects (see below) from the mother’s blood. The test thus represents a risk-free alternative (= “non-invasive prenatal testing”, NIPT or “Non-Intrusive Pregnancy Diagnostic Test”, NIPDT) to conventional invasive examination methods, such as amniocentesis. The pregnant woman should be at 9+0 weeks of gestation (SSW) or above. As a screening test in prenatal diagnosis (PND; prenatal diagnosis), the PraenaTest is used to assess risk for:

• Chromosomal disorders – chromosomal abnormalities that may affect the number of chromosomes (numerical chromosomal abnormality: one chromosome too many or too few) or the structure of chromosomes (structural chromosomal abnormality):
  • Trisomy (unusual meiosis (maturation division) of oocyte (egg) or sperm that results in a chromosome or part of a chromosome being present in triplicate (trisome) rather than in duplicate (disome) in all or some of the body’s cells)
    • Trisomy 21 (Down syndrome; synonyms: “mongolism”)
      • Triplication of the genetic material of chromosome 21.
      • Children have weak to moderate mental retardation
      • Often malformations of internal organs (eg vitia / heart defects).
      • Most common trisomy: 1 in 740 newborns is affected.
    • Trisomy 18 (Edwards syndrome; synonyms: E1 trisomy, trisomy E).
      • Triplication of the genetic material of chromosome 18.
      • High miscarriage rate (miscarriage rate).
      • Children are born with severe malformations
      • Short life expectancy
      • 1 in 5,000 newborns is affected
    • Trisomy 13 (Patau syndrome; synonyms: Patau syndrome, Bartholin-Patau syndrome, D1 trisomy).
      • Triplication of the genetic material of chromosome 13.
      • High miscarriage rate (miscarriage rate).
      • Children are born with severe congenital (congenital) vitia (heart defects)
      • Usually die within the first year of life
      • 1 in 16,000 newborns is affected
• Disorders/maldistribution of sex chromosomes X, Y and resulting hereditary diseases.
  • Klinefelter syndrome – gonosome (sex chromosome) abnormality of the male sex resulting in primary hypogonadism (gonadal hypofunction). It occurs approximately once in 500 male newborns.
  • Turner syndrome (synonym: Ullrich-Turner syndrome) – girls/females with this disorder have only one functional X chromosome instead of the usual two (monosomy X); it is the only viable monosomy in humans and occurs approximately once in 2500 female newborns.
  • Triple X syndrome (XXX) / Trisomy X: In triple X syndrome, the X chromosome is present three times. This disorder affects only girls and occurs approximately once in 1,000 female newborns
  • XYY syndrome / Diplo Y syndrome: In diplo Y syndrome, which also affects only boys, there is an extra Y chromosome in the cells. It occurs circa once in 1,000 births of male newborns

Furthermore, the PraenaTest can be used to determine the sex of the unborn. The accuracy here is > 99%.

Before the examination

The PraenaTest (NIPT) requires medical information and genetic counseling in accordance with the German Genetic Diagnosis Act (GenDG). The NIPT currently allows reliable statements on the probability of trisomy 21, 18, 13, but no statements on structural malformations. However, these make up the majority of perinatally relevant anomalies. Also, most other chromosomal defects and syndromal conditions cannot be detected. Note: In twin pregnancies, after artificial insemination, and in obesity, NIPT has a higher failure rate and there are limited data on test performance.

The procedure

The test is a noninvasive molecular genetic prenatal diagnostic test to determine chromosomal disorders, in the unborn child: trisomy 21, 18, and 13, Klinefelter syndrome, Turner syndrome, triple X syndrome, and XYY syndrome. It is a non-invasive prenatal diagnosis (NIPD) on fetal (child) DNA (genetic material; cell-free DNA; cfDNA) obtained from maternal blood. It thus replaces the previous first trimester screening (ETS) and amniocentesis (amniocentesis) for the question of trisomy 21.A case of trisomy 21 (Down syndrome) in

Number of pregnancies	Age of pregnant women
1.383	25-year-old women
338	35-year-old women
84	40-year-old women
32	45-year-old women

International studies demonstrate a sensitivity (percentage of diseased patients in whom the disease is detected by use of the test, i.e., a positive test result occurs) of the test of 99.1% and a false positive rate of 0.3%, i.e., a pregnant woman with an intermediate risk of, say, 1: 100 for fetal trisomy 21 would have a 3:1 risk of giving birth to a child with trisomy 21 after a positive test and a 1: 11,000 risk if the test is negative. Material needed

• Blood serum

Preparation of the patient

• Not necessary

Disruptive factors

• None

Indications (areas of application)

• Pregnant women, from 9+0 weeks of gestation (SSW), who have an increased risk of chromosomal changes and disorders/maldistribution of sex chromosomes in the unborn child.
• Determination of fetal sex (notification of the result may be made only after the 14th SSW post menstruationem).

Interpretation

• The PraenaTest (NIPT) is a screening test. If the NIPT is abnormal, diagnostic puncture must be offered obligatorily. The indication for termination of pregnancy must not be based on an isolated NIPT finding.
• An inconclusive NIPT is a finding that requires clarification. In this collective, more chromosomal defects are found, especially trisomies 13 and 18 and triploidies.