FETAL CHROMOSOMAL ABNORMALITIES
Fetal chromosomal abnormalities occur when a fetus happens to have either an incorrect number of chromosomes or chromosomes with structural errors. Such chromosomal imperfections may translate to the development of birth defects, congenital disorders, or miscarriage. Fetal chromosomal abnormalities diagnosis is based on a number of specific tests performed during pregnancy, such as regular US scan of your fetus, alpha-fetoprotein blood test, chorionic villus sampling. Below you can find more detailed information about fetal chromosomal abnormalities and diagnostics services to detect them.
It is uncommon for foetuses to develop chromosome abnormalities. However, many parents are concerned that their baby might be affected. There are several tests available in this day and age to screen and diagnose chromosomal abnormalities at an early stage of the pregnancy.
WHAT ARE CHROMOSOMES?
Chromosomes are thread-like structures that can be found within the central part (nucleus) of living cells. They are composed of DNA (deoxyribonucleic acid) and appear in the physical form in which our genes exist. A healthy human being has a total of 46 chromosomes. Two of these are the sex chromosomes known as chromosome X and Y. The composition of the chromosomes for:
- Females: 46XX
- Males: 46XY
Each half of the pair of chromosomes is inherited from each parent. The chromosomes house a large number of genes. Abnormalities in the fetus can involve the chromosomes alone or it can involve one or more genes.
ARE GENE ABNORMALITIES ALWAYS INHERITED?
Most gene abnormalities do not result in an abnormality in the baby unless an abnormal gene is inherited from both the mother and the father. Normally, if only one copy of a gene is defective, the gene that is not defective from the other parent will take over. Chromosome abnormalities on the other hand are more common than is generally realized.
- More than 50 per cent of miscarriages in the early stages of pregnancy are caused by abnormalities in the chromosomes
- About 0.5 to 1 per cent of all births, a recognisable chromosome abnormality is detected
Down’s syndrome is the most well-known chromosomal abnormality. Individuals affected by the condition have 3 sets of no. 21 chromosomes, they have 3 sets. The effects of this syndrome include:
- Low IQ
- Distinct features (short limbs and a characteristic wrinkle around the eyes)
- Heart defects are also common and are present at birth
Babies born with extra chromosome no. 13 (Patau’s syndrome) or no. 18 (Edward’s syndrome) seldom survive beyond birth. These syndromes are less common than Down’s syndrome. If a baby has a 45X0 composition in the chromosomes as well as other sexual chromosomes missing, it will result in girl with Turner’s syndrome. Girls with this syndrome are short and are u able to have children because their ovaries are underdeveloped. Their mental development is normal, but certain heart defects are common with this syndrome.
Fetal chromosomal abnormalities diagnosis
- Ultrasound scan – a simple non-invasive regular morphology scan helps to monitor fetus development and find out any deviations from normality. At the end of first trimester, doctor will measure the nuchal fold thickness in order to rule out Down`s syndrome.
- Alpha-fetoprotein test (AFP) or multiple marker test. Alpha-fetoprotein is produced by the fetus and can be detected in mom`s blood sample. This test is usually done between weeks 16 and 18 of pregnancy. The results can disclose possible presence of birth defects. It can also indicate chromosomal abnormalities in the developing baby.
- Chorionic villus sampling (CVS) is a prenatal test that helps to detect fetal chromosomal abnormalities such as Down syndrome. To perform this test your doctor will take some cells from tiny finger-like protrusions on the placenta, which are called the chorionic villi and send those samples to a lab for genetic analysis, where specialists will grow the harvested cells in order to analyse chromosomes.