Northwestern Prenatal Genetic Centre
Training Centre of Ott's Institute of Obstetrics & Gynecology RAMS
14-th Liniya Vasilyevskogo ostrova, 7
+7 (812) 677-14-08, 921-26-32, 921-26-37
The modern level of medical technology allows for screening pregnant women and identification among them risk groups by the presence of Down syndrome and other chromosomal disease in the fetus. This can be done already from 11 weeks of pregnancy. The combination of ultrasound and biochemical studies at 11 -13 weeks is recognized as the most effective.
From 11 to 13 weeks the ultrasound markers (signs) of fetal chromosomal pathology can be detected. It is the increase in thickness of fetal nuchal translucency and the lack of nasal bone.
The nuchal translucency (NT) is a collection of fluid beneath the fetal skin in the region of the fetal neck. This is present and seen in all fetuses in early pregnancy. The fluid collection is however increased in many fetuses with Down's syndrome and many other chromosomal abnormalities. This is normally less than 2.5mm and when seen increased (greater than 2.5mm, see image on the right) may indicate the baby has Down syndrome or may indicate another chromosomal abnormality. The nuchal translucency normally disappears after 14 week of pregnancy that is why it is so important to have the nuchal translucency measured with an ultrasound between 11 to 14 weeks of pregnancy. The nasal bone normally becomes visible at the scan since 10 weeks of pregnancy. For a fetus having no visible nasal bone at this period it can also be the sign of chromosomal abnormalities.
Subject to the necessary standards, ultrasound at 11-13 weeks of pregnancy can reveal up to 80% of fetuses with
Down syndrome and other chromosomal disorders.
Biochemical examination of the mother’s blood let to determine concentration of different kinds of proteins produced in placenta: РАРР-А and β- HCG .There are certain standards of content of these proteins in the blood for every week of pregnancy and in case of some chromosomal pathologies the level of these proteins will be different.
It’s proved that most significant differences in normal and abnormal proteins concentration is visible in period of 10-12 weeks of pregnancy. Biochemical examination of the mother’s blood at this period allows to reveal about 70% of fetuses with Down’s syndrome.
Combination of ultrasound diagnosis and blood examination allows to increase the detection rate of fetuses with
Down syndrome up to 85%.
Today this method of screening is the most efficient way to detect fetuses at risk for Down syndrome or any other chromosomal diseases.