Learn about the concept of Hidden Vanishing Twin and its correlation with NIPT (Non-Invasive Prenatal Testing) in this comprehensive guide.
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What is Vanishing Twin?
In English, “Vanishing” means “to disappear.” Therefore, a Vanishing Twin refers to the phenomenon where one of the originally twin fetuses naturally disappears, leaving only one.
In many cases, this occurs due to genetic abnormalities that make survival impossible, resulting in the fetus shrinking or disappearing.
What is “Hidden Vanishing Twin”?
When initially diagnosed as a twin pregnancy, if during prenatal check-ups only one fetus is confirmed, the diagnosis of Vanishing Twin occurs.
However, in some cases, despite being a twin pregnancy, it may be diagnosed as a singleton. This could happen because one fetus is too small to detect or its heartbeat has ceased, making it difficult to find at an early stage before heartbeat activity can be observed, and therefore cannot be confirmed through ultrasound (sonogram) examination.
Among cases where only one fetus was initially considered during pregnancy, those where one of the twin fetuses has disappeared are defined as “Hidden Vanishing Twin.”
Issues with examination results in the case of “Hidden Vanishing Twin”
In genetic testing, in cases of “Hidden Vanishing Twin” where one fetus has disappeared or diminished but is recognized as a singleton, it’s common to inadvertently pick up the genes of the vanished or diminished fetus. Even if the fetus is small in size, highly accurate NIPT (Non-Invasive Prenatal Testing) can detect these genes in the mother’s blood.
Generally, the causes of Vanishing Twin are known to be related to chromosomal abnormalities such as Trisomy 18 or Trisomy 13.
If a fetus with trisomy disappears and NIPT (Non-Invasive Prenatal Testing) is conducted, it will be detected as positive. However, if amniocentesis is performed for the surviving fetus for definitive diagnosis, the result will be negative. In this case, the NIPT result would be a false positive.
However, in the case of “Hidden Vanishing Twin,” a positive result in genetic testing is indeed a valid result.
Types of NIPT (Non-Invasive Prenatal Testing) and “Hidden Vanishing Twin”
Generally, NIPT (Non-Invasive Prenatal Testing) is thought to have only one method, but there are currently several types depending on the type of device used.
The Veriseq V2 system, which is a widely used type of NIPT (Non-Invasive Prenatal Testing) device based on Whole Genome sequencing, cannot distinguish between the genes of the two fetuses in the case of a “Hidden Vanishing Twin.” Therefore, it is not possible to determine which fetus has abnormalities. While this may not be a significant issue when the pregnancy is known to be a twin pregnancy from the beginning, in the case of “Hidden Vanishing Twin,” the NIPT results may be falsely positive.
On the other hand, the Cyprus method, a Target type of NIPT, can differentiate between the genes of the two fetuses. This allows for diagnosing one fetus with trisomy while the other is normal.
If NIPT is being considered for someone already diagnosed with Vanishing Twin, it’s recommended to opt for the Cyprus method. However, it’s important to note that the Cyprus method can only detect a limited number of chromosomes (13, 18, 21) due to its nature of deeply analyzing each one.
In contrast, the Veriseq V2 system, which uses the Whole Genome type of testing, can examine all chromosomes. This means it can detect the total number of chromosomes as well as partial deletions or duplications of autosomes.
Thus, by employing multiple testing methods, NIPT can now conduct a wide range of examinations. For those considering NIPT, choosing the appropriate testing method based on the situation is advisable.
Learn about the concept of Hidden Vanishing Twin and its correlation with NIPT (Non-Invasive Prenatal Testing) in this comprehensive guide.
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Article Editorial Supervisor
Private: Dr. Hiroshi Oka
NIPT Specialist Clinic, Doctor of Medicine
Graduated from Keio University, School of Medicine
