How Is Trisomy 13 Diagnosed?

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Chromosomal abnormalities are one of the most common causes of miscarriage and stillbirth. In a condition known as trisomy, an affected individual has three copies of a particular chromosome instead of two (human beings are supposed to have 46 chromosomes, which come in 23 pairs). There are several different types of trisomies; these include Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). Trisomy 13 is the most severe of the trisomies. 

Babies with trisomy 13 will likely have characteristic physical abnormalities, intellectual disabilities, and problems with their internal organs. The majority of affected babies die within the first month or within the first year after birth due to the health complications associated with the condition. 

Approximately one in 16,000 babies are born with trisomy. Researchers believe that around 95% of babies with trisomy 13 are miscarried or stillborn. No one knows why some survive to term while others do not. Many babies who do survive birth after a trisomy 13 diagnosis do not live past their first week. Only 5 to 10% make it to their first birthday.

Diagnosing Trisomy 13

Prenatal screening tests such as the alphafetoprotein test and a pregnancy ultrasound can reveal markers of possible chromosomal conditions, but they cannot provide a diagnosis. Only genetic tests such as amniocentesis and chorionic villus sampling (CVS) can provide a definitive diagnosis. It's also possible that trisomy 13 can be revealed as the cause of a pregnancy loss if the couple seeks genetic karyotyping after a miscarriage or stillbirth.

Common physical signs in babies with trisomy 13 include small or poorly developed eyes, extra fingers and/or toes, cleft lip or palate, and decreased muscle tone. 

Types of Trisomy 13

As with other trisomy disorders, there are three types of Patau syndrome:

  • Full trisomy 13: The most common type. People with this type have three full copies of chromosome 13.
  • Partial trisomy 13: People have two full copies of chromosome 13 and an extra part of chromosome 13.
  • Mosaic trisomy 13: Some of the body's cells had three copies of chromosome 13 whereas others have two normal copies.

Risk of Recurrence

Most of the time, the cause of trisomy 13 is a random error in cell division during the formation of the egg or sperm, meaning the problem is present at the time of fertilization. In this case, the disorder is unlikely to reoccur. In rare cases, the parent may have a balanced translocation involving chromosome 13. People with a balanced translocation have an increased risk of having a child with partial trisomy 13 again. 

Proceeding After a Trisomy 13 Diagnosis

One of the first questions you may be asked if your baby receives a diagnosis of trisomy 13 is whether you want to continue the pregnancy or pursue intensive intervention if the baby is born with health problems. During pregnancy, some parents choose to terminate babies diagnosed with trisomy 13 due to the generally poor prognosis and the desire to not prolong the grief of the loss. Others continue the pregnancy due to personal beliefs against abortion, or because they feel they would rather have some time with the baby, even if it turns out to be short. The same applies to babies diagnosed after birth—some parents choose comfort care only, while others opt for intensive medical interventions, even though the chances appear slim that the baby will survive infancy.

A 2017 study showed that performing congenital heart surgery in babies with trisomy 13 may increase their chances of survival. There is still not sufficient research to support this claim, however, and the study researchers still maintain that the surgery carries a high risk for infants who already have such a low chance of survival.

A Word From Verywell

If your baby has been diagnosed with trisomy 13, you may experience any number of emotions from grief to anger to simply feeling overwhelmed. It's fine to take your time and process the situation before moving forward and making decisions or plans. There is no "right" way to feel and no single "correct" course of action to take with these diagnoses. You have the right to use your own judgment in making a decision, and the answer ultimately is different for everyone.

Regardless of what you decide, it is fine to grieve the loss of the baby you were expecting to have. It can be helpful to join support groups for parents of babies with trisomy 13 or other serious chromosomal disorders.

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