Down Syndrome or trisomy 21 is a chromosomal abnormality with an extra chromosome 21 added. Normally, during fertilization, both the ovum and the sperm give 23 chromosomes to get a complete set of 46 chromosomes or 23 chromosomal pairs. In cases where an extra copy of a chromosomal pair is transmitted from the ovum or sperm, the number of chromosomes increases and they become 3 for the designated pair instead of 2. This condition is called trisomy. It can be obtained with each of the chromosomal pairs. Some conditions are lethal at the beginning of pregnancy and lead to miscarriage and others may have greater survival. But all these trisomies lead to different deviations in anatomy, physical or mental development. The most common trisomy is the 21st chromosomal pair or Down Syndrome. Other common trisomies are the 13th or Patau Syndrome and the 18th, Edwards Syndrome.
Down syndrome is named after John Langdon Down, the first scientist explaining its origin. In general, trisomy 21 occurs in 1 out of 500 pregnant women in 20th week of pregnancy.
Down syndrome is due to an additional copy of chromosome 21 and is correlated positively with a woman’s age, especially after 35 years. That is why in the past all women who turned 35, were offered amniocentesis. With modern methods such as combined screening test and cff DNA, the invasive methods for detecting the three most common trisomies 21, 13 and 18 should not be used as the first means, but should have a gradation of the studies to reduce unwanted consequences. Medicine has generally made significant progress in non-invasive diagnostic methods that should be used in full before invasive procedures. Everything else is an inappropriate and incompetent intervention with taking unjustified risk.
Unlike most trisomies, children born with Down syndrome are viable. In 50% of the cases of trisomy 21, no ultrasound markers can be found to detect it. The remaining 50% can detect one or multiple anomalies. These markers may be more important or secondary. Among the main abnormalities are heart abnormalities with interventricular defect, interauricular ventricular defect, abnormalities of the digestive tract with obstruction of the esophagus, of duodenum, abdominal wall defects, brachycephaly, or a lag in intrauterine development. Secondary ultrasound markers include: nuchal edema, short limbs, hypoplasia, minor hydronephrosis, mild ventriculomegaly, sandal gap, small ears, large tongue, and so on.
Children born with Down syndrome have a stronger or less apparent phenotype with a mongoloid face, a monkey palmar crease, a large tongue outside the mouth. In 50% of those affected there is a mental retardation. In a large percentage of these cases, these children experience about 20 to 30 years due to multiple abnormalities. Those with mental retardation need special care. Among other children, there may be an opportunity to study and even find work.
And here’s the question - why do we need to explore if your child can have Down syndrome!? The analysis, particularly combined screening test and cff DNA, are non-invasive procedures related only to taking venous blood from the pregnant woman. These methods do not pose a risk either to you or your baby. With these two methods, screening is also done for Patau and Edwards syndromes. Detecting some of these syndromes would be extremely useful for both you as a prospective parent and for us, the medics. It is important for parents because they will be able to make the right decision for them - whether to continue pregnancy or discontinue it. If you do not want to have a child with some of these syndromes, the end of the first trimester is the most appropriate and has the least hazards for you and your childbearing ability for the future. If you decided to continue pregnancy, you will become more aware of this condition, look for more information, and be more prepared to take care of your child and what you will experience after your delivery. For us, doctors, it is important to be able to track pregnancies more closely, to look for anomalies in more detail, to plan birth, and last but not least to give you advice on subsequent pregnancies, to direct you to genetic counseling if necessary and determine the risk of recurrence of this syndrome in the next pregnancy.
This is trisomy 13, or an extra copy of chromosome 13 that is attached to another chromosome. Here, too, there is a positive correlation with maternal age.
Ultrasonic markers for Patau syndrome are central nervous system abnormalities - holoprosencephaly, corpus callosum aggression, small brain abnormalities, cardiac abnormalities, urinary system abnormalities, skeletal abnormalities, intrauterine developmental defects, abdominal wall defect. In addition, nuchal oedema, hard palate defect, upper lip defect, eye abnormalities, etc. are observed.
The prognosis for Patau’s syndrome is serious and 95% fatal. A large percentage of the affected fetuses die in utero, the few survivors die within a few months of their birth. Those born suffer from psychomotor disorders, blindness, epilepsy, apart from the abnormalities listed above.
Edwards syndrome is trisomy 18 and is due to an extra copy of 18 chromosome. Trisomy 18 also has a positive correlation with maternal age.
The main ultrasound markers are central nervous system abnormalities such as corpus callosum aggression, cerebral anomalies, heart abnormalities, abnormalities of the excretory system, skeletal abnormalities, retardation in intrauterine development, abdominal wall defect. Other abnormalities are Strawberry-shaped skull, choroid plexus cysts, and others.
Trisomy 18 is a lethal condition. Only 5% of fetuses can reach a term and survive for only a week. Those borns have psychomotor and mental retardation, reduced hearing and vision. Among other anomalies, these children have a predisposition to infections, which is another reason for the high mortality.