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About Trisomy 18

Trisomy 18, also known as Edwards syndrome is a chromosomal abnormality. Trisomy is the condition of having three copies of chromosome, instead of two.

When an egg and sperm join to form an embryo, their chromosomes combine and are paired in two. Each baby gets 23 chromosomes from the mother’s egg and 23 chromosomes from the father’s sperm, making a total of 46 chromosomes.

Trisomy 18 has an extra chromosome 18, which results in an abnormal triple cell division during the baby’s development. It is caused by part or all of the extra chromosome 18. Screening for chromosomal disorders is performed during the 1st trimester. Some doctors prefer to have the screening done in the 2nd trimesters between the 15th to 20th week. The screening combines an ultrasound and a material blood test.

A Trisomy 18 error occurs around 1 in 6000 live births. 80% of the babies effected by the Trisomy 18 are females. The numbers of total births is much higher because it includes significant numbers of stillbirths, which occurs during the 2nd and 3rd trimesters of pregnancy. Most live births only live days or weeks after birth, with very few making it to their first birthday.

There are three types of Trisomy 18:
Full Trisomy 18
This is when the extra chromosome is in every chromosome 18 cell. This is the most common found in Trisomy 18.
Partial Trisomy 18
This is when there is only part of an extra chromosome 18. The extra one may be attached to another chromosome in the egg or sperm. This type of Trisomy 18 is the very rarest.
Mosaic Trisomy 18
This is when the extra chromosome 18 is only in some the baby’s cell. This form of Trisomy 18 is also rare.

Physical abnormalities found in Trisomy 18 babies are clenched of the hand, with overlay of index and pinky fingers, low set ears, rocker bottom feet, cleft palate, wide spaced eyes, dropping of the upper eyelids, low birth weight, growth delays and feeding problems. Feeding tubes is inserted through the nose are more commonly used when feeding a Trisomy 18 baby. Internal abnormalities are heart defects, kidneys, lungs and intestinal problems.

There are many types of trisomy. Trisomy 18 is the second most common. Trisomy 21 is most common of the trisomy defects. Trisomy 21 is down syndrome.

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