What is t18

When this cell contributes the extra chromosome 18 to the embryo, trisomy 18 results. Rarely, mosaic trisomy 18 may occur when the error in cell division occurs after fertilization. These babies have some cells with an extra chromosome 18 and others with the normal number. These babies usually have milder forms of trisomy Babies with trisomy 18 have a unique group of characteristics and can be diagnosed by physical examination. To confirm the diagnosis, a small blood sample can be taken and the chromosomes can be analyzed to determine the presence of an extra chromosome Chromosomal abnormalities can also be diagnosed before birth by analyzing cells in the amniotic fluid obtained by amniocentesis , or from the placenta, obtained by chorionic villus sampling CVS or from the fetal blood obtained by cordocentesis.

Fifty per cent of babies born with trisomy 18 survive beyond their first six to nine days. It is difficult to predict the life expectancy of a baby with trisomy 18 if the baby does not have any immediate life-threatening problems. However, the average age of the mother at delivery of a baby with trisomy 18 is 32 years. Parents of a baby with trisomy 18 are encouraged to seek genetic counselling.

This can help parents to:. Some infants will be able to survive to be discharged from the hospital with home nursing support to assist with care by the parents. And although 10 percent or more may survive to their first birthdays, there are children with Trisomy 18 that can enjoy many years of life with their families, reaching milestones and being involved with their community. A small number of adults usually girls with Trisomy 18 have and are living into their twenties and thirties, although with significant developmental delays that do not allow them to live independently without full time caregiving.

This looks at the chance of your baby having the condition. This screening test is called the combined test and it works out the chance of a baby having Edwards' syndrome, Down's syndrome and Patau's syndrome.

During the test you'll have a blood test and an ultrasound scan to measure the fluid at the back of your baby's neck nuchal translucency. Read more about screening for Edwards' syndrome at 10 to 14 weeks.

If it's not possible to measure the fluid at the back of your baby's neck, or you're more than 14 weeks pregnant, you'll be offered screening for Edwards' syndrome as part of your week scan.

This is sometimes known as the mid-pregnancy scan. It's an ultrasound scan that looks at how your baby is growing. Screening cannot identify which form of Edwards' syndrome your baby may have, or how it will affect them. If the combined test shows that you have a higher chance of having a baby with Edwards' syndrome, you'll be offered a test to find out for certain if your baby has the condition.

This diagnostic test involves analysing a sample of your baby's cells to check if they have an extra copy of chromosome These are invasive tests that increase your chance of having a miscarriage.

Your doctor will discuss this with you. A specialist doctor obstetrician or midwife will explain what the screening results mean and talk to you about your options. This is a very difficult situation and it's normal to feel a whole range of emotions. It may help to talk to your doctor, family and friends, or partner about what you're thinking and how you're feeling. If you're told your baby has Edwards' syndrome, either before birth or afterwards, you'll be offered support and information.

You can visit the SOFT UK website for support and more information on Edwards' syndrome, and to contact other families affected by the condition.

You can also contact Antenatal Results and Choices ARC , which has information about screening tests and how you might feel if you're told your baby does have, or might have, a problem. ARC has a helpline that can be reached on , or from a mobile, Monday to Friday, 10am to 5.

The helpline is answered by trained staff, who can offer information and support. In these people, the condition is called mosaic trisomy The severity of mosaic trisomy 18 depends on the type and number of cells that have the extra chromosome. The development of individuals with this form of trisomy 18 may range from normal to severely affected.

Very rarely, part of the long q arm of chromosome 18 becomes attached translocated to another chromosome during the formation of reproductive cells eggs and sperm or very early in embryonic development. Affected individuals have two copies of chromosome 18, plus the extra material from chromosome 18 attached to another chromosome. People with this genetic change are said to have partial trisomy If only part of the q arm is present in three copies, the physical signs of partial trisomy 18 may be less severe than those typically seen in trisomy If the entire q arm is present in three copies, individuals may be as severely affected as if they had three full copies of chromosome Most cases of trisomy 18 are not inherited, but occur as random events during the formation of eggs and sperm.

An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of chromosome If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 18 in each of the body's cells.

Mosaic trisomy 18 is also not inherited. It occurs as a random event during cell division early in embryonic development. As a result, some of the body's cells have the usual two copies of chromosome 18, and other cells have three copies of this chromosome. Partial trisomy 18 can be inherited. An unaffected person can carry a rearrangement of genetic material between chromosome 18 and another chromosome.