Sonographic Examination of Fetal Nuchal Translucency: First Trimester Screening

The likelihood of having a child with trisomy 21 (Down syndrome) increases as the mother ages. In trisomy 21, there is an abnormal chromosomal change in the child in which the entire 21st chromosome or parts of it are present in triplicate (trisomy). In addition to physical characteristics considered typical for this syndrome, the cognitive abilities of the affected person are usually impaired. Therefore, prenatal diagnostics (prenatal diagnosis of the unborn child) is recommended for all women over 35 years of age. The non-invasive molecular biological blood test (NIPT) for prenatal diagnosis of trisomies does not make prenatal diagnosis by ultrasound unnecessary:Note: 90 percent of fetal or child malformations are not of chromosomal origin at all. The measurement of nuchal translucency (NT) as part of first trimester screening (ETS; ETT, first trimester test), in combination with other parameters (see below), makes it possible to determine an individual risk of developing fetal trisomies 21, 18 and 13 for each patient. This may be lower than the risk based on age alone. This may thus facilitate the decision for or against more invasive testing, such as amniocentesis.

Indications (areas of application)

  • Age over 35 years
  • Child with trisomy 21 (Down syndrome) in the family
  • Child with heart defect in the family
  • Multiple pregnancies
  • Diabetes mellitus
  • Gestational diabetes
  • Maternal metabolic diseases
  • Drug and medication addiction
  • Alcohol abuse
  • Infections or X-ray examinations in early pregnancy
  • Chemical contact
  • Unexplained neonatal deaths in the father’s or pregnant woman’s family.
  • Marriages within the kinship

The procedure

Ultrasound is used to assess the nuchal fold thickness in the fetus at 10-14 weeks of gestation. Special computer programs calculate the individual risk of developing fetal trisomies 21, 18, and 13 from the nuchal fold thickness, week of gestation, crown-rump length (SSL), and maternal age. The accuracy of the test can be further improved by combining it with laboratory chemistry tests-measurement of the pregnancy hormone β-hCG and pregnancy associated plasma protein A (PAPP-A). Other possible causes of increased fetal nuchal translucency include:

  • Aortic isthmic stenosis (vascular malformation: narrowing of the aorta (main artery) in the region of the aortic arch).
  • Fetal cardiac dysfunction (malfunction of the heart).
  • Venous (vein-related) congestion in the head and neck area (eg, by diaphragmatic hernia, shortening of the ribs in skeletal dysplasia / developmental disorders of cartilage or bone tissue).

In addition to determining fetal nuchal translucency, early screening for fetal malformations can be performed at the same time. Malformations such as acrania (malformation with complete absence of the skull and brain), anencephaly (lack of closure of the skullcap, also missing to varying degrees parts of the bony roof of the skull, meninges, scalp and brain), alobar holoprosencephaly (HPE; malformation in the area of the forebrain and face), ectopia cordis (heart is located outside the chest), large omphalocele (umbilical cord hernia (hernia of the umbilical cord) resulting in the displacement of some abdominal organs to the outside (physiological umbilical hernia) through the abdominal wall of the unborn child), large gastroschisis (abdominal wall defect to the right side of the umbilicus) and megacystis (conspicuously large urinary bladder) can be detected 100 percent of the time during first trimester screening. Note: Early screening for fetal malformations requires a high-resolution ultrasound machine and an experienced examiner. Additional notes

  • In terms of detecting the common chromosomal abnormalities (trisomy 13, 18, and 21), NIPT (molecular genetic blood test to detect cell-free DNA) is clearly superior to first trimester screening (ETS).
  • Detection of nuchal septa indicates chromosomal abnormalities regardless of fold thickness.In one study, an evaluation of this showed that septated nuchal folds have about a 40-fold higher risk of chromosomal abnormalities than unseptated folds.
  • CONCLUSION: First trimester screening should continue to be performed to assess early pregnancy. However, every pregnant woman should also benefit from the excellent test quality of molecular genetic blood tests (cell-free DNA; cfDNA; e.g., NIPT, Praenatest).

Benefit

The main advantage is that ultrasound examination is completely safe for both mother and child. Invasive methods, that is, intrusive examination methods such as amniocentesis and chorionic villus sampling, always have a low risk of miscarriage (abortion). Fetal nuchal translucency testing is very reliable for the diagnosis of Down’s disease. Rarely are false-positive diagnoses made, meaning that the diagnosis of Down’s disease would not be confirmed by subsequent testing. If a lower risk than age-appropriate is determined, invasive testing may not be necessary. Therefore, this method is highly recommended, especially for women over 35 years of age. Ultrasound examination of fetal nuchal translucency is a risk-free and safe method to minimize the individual risk of having a child with Down’s disease. Thus, nuchal translucency examination is an essential diagnostic test for the health of your unborn child.