Confined Placental Mosaicism (CPM)

Because the placenta and the baby come from the same cells, they have exactly the same amount of chromosomes most (98-99%) of the time. In approximately 1-2% of all pregnancies, the placenta can actually have a different chromosome makeup from the baby. This is called confined placental mosaicism (CPM).

When it comes to genetic testing, CPM is important to remember particularly when it comes to CVS procedures. If someone has a CVS and the results show an extra or missing chromosome, we know that the most likely thing is that the pregnancy also has that extra or missing chromosome. However, 1-2% of the time, that extra or missing chromosome is only found in the placenta and not in the pregnancy.

The exact reason for this difference is unknown, but it is thought that after the placenta and the baby separate, some sort of error happens during cell division in the placenta, which causes some of the cells to have an extra or missing chromosome.

If CPM is suspected on a CVS result, it may be recommended to perform an amniocentesis procedure to confirm. Because the cells obtained from an amniocentesis are from directly around the baby, it is more accurate in determining whether the pregnancy actually has the extra or missing chromosome.

Related Articles

  • A CVS procedure can be done in the doctor's office by a high-risk pregnancy doctor called a perinatologist. CVS is an outpatient procedure, meaning you can usually go home soon afterward. Most women find that it can be uncomfortable and many compare it to having intense menstrual cramps, but generally…
  • The type of results may vary depending on the type of testing that is done on the CVS sample. The four main types of testing that can be done on CVS samples are: traditional chromosome analysis (also called a karyotype), chromosomal microarray, familial mutation testing, and fluorescent in-situ hybridization (FISH).…
  • This can be difficult news to hear, and everyone handles situations like this in different ways. It is often helpful to talk with your doctor or genetic counselor to make sure any questions that you have are answered, particularly if the results are complex or confusing. Even if you are…
  • The decision of whether or not to have a diagnostic test, such as a CVS, can be a difficult decision to make. Your genetic counselor can help answer any questions, and help you come to the decision that is best for your personality, beliefs, and values. Some things that may…

Last updated on Apr 7th, 2018