The overall mean gestational age found at detection was 19,5 weeks, with a range from 11 to 36 weeks. For trisomy 13 the mean gestational age was 22,8 weeks, with a range from 11 to 36 weeks. For trisomy 18 this was 17,4 weeks, with a range from 11 to 33 weeks.

What causes a false positive for trisomy 13?

Possible causes of false positive results for trisomy 13 from NIPT include: Confined placental mosaicism (CPM) This is caused by a population of cells in the placenta with three copies of chromosome 13 instead of the usual two. These cells are confined to the placenta and are not present in the baby.

What is a normal trisomy?

Trisomy (‘three bodies’) means the affected person has three copies of one of the chromosomes instead of two. This means they have 47 chromosomes instead of 46. Down syndrome, Edward syndrome and Patau syndrome are the most common forms of trisomy.

What is considered high risk for trisomy 13?

Nevertheless, some risk factors exist. For example, the chance of having a baby with Trisomy 13 is higher in older mothers. In other cases, Trisomy 13 can be inherited due to a familial chromosome rearrangement called a translocation. Trisomy 13 is never the result of anything a mother or father did, or didn’t do.

How common is trisomy 13 in pregnancy?

The incidence of trisomy 13 Trisomy 13 occurs in 1 in 6,000 to 1 in 29,000 live births. The overall prevalence is higher in pregnancy because many babies with trisomy 13 will miscarry before delivery. Although a pregnant person could have a baby with trisomy 13 at any age, the chance increases with maternal age.

What is a good trisomy 21 result?

A standard risk cutoff is used to determine when the test is considered “positive.” Most laboratories use a risk cutoff of 1/270, which is equal to the second-trimester risk of trisomy 21 in a 35-year-old woman. 13 A positive test is an indication for amniocentesis (Figure 2).

What is trisomy 13 in pregnancy?

Trisomy 13 happens when there is an extra copy of chromosome 13 in either the egg or the sperm before conception. This means that the baby will have three copies of chromosome 13 instead of two. The extra chromosome can cause differences in the way a baby develops. Most often, trisomy 13 happens by chance.