A vanishing twin, also called twin embolisation syndrome, is the term for a fetus in a multi-gestation pregnancy which dies in utero and is then partially or completely reabsorbed by the mother. Occasionally, rather than being completely resorbed, the dead fetus will undergo mechanical compression by its wombmate(s), resulting in a flattened, parchment-like state known as fetus papyraceus. If the fetus is absorbed completely, there are usually no further complications to the pregnancy. However, if it is not, and the event occurs in the second or third trimester, serious complications may include premature labor, infection due to the demise of the fetus, and hemorrhage. Even at the end of the pregnancy, a low-lying fetus papyraceus may block the cervix and require a cesarean to deliver the living twin.

According to some researchers, vanishing twins occur in up to one out of every eight pregnancies and may not even be known in most cases. Since it is hypothesized that some instances of vanished twins leave no detectable trace, it is impossible to say for certain how frequent the phenomenon is.

The Vanishing Twin Syndrome has been cited by biotech company Acu-Gen as an ad hoc hypothesis to explain false results of the company's Baby Gender Mentor test. According to the company, on occasions where their pregnancy gender test has apparently given the incorrect gender of the fetus, the apparent mistake can be explained by a fetus having been present at the time of testing, but later being reabsorbed as a vanished twin.

It has been speculated that the children born in such a pregnancy may have some memories of their vanishing twins, and may feel lonely because of this. There is no scientific evidence to support this claim. Researchers of the paranormal, such as George Noory's talkshow Coast to Coast, have discussed the alleged phenomenon.

A wombtwin is a term used since 2003 to describe an embryo or fetus that was a member of a twin pair or triplet set and which died in the womb. The loss of a twin very early in pregnancy has been called "vanishing twin" phenomenon since the 1980s when twin pregnancies were made visible by means of ultrasound (sonograph) scanning. Two developing gestational sacs are seen at the first ultrasound scan but only one is visible at the second scan. The wombtwin dies owing to a poorly implanted placenta; a developmental anomaly that may cause major organs to fail or be missing completely; there may be a chromosome abnormality incompatible with life. Frequently the twin is a blighted ovum, that never developed beyond the very earliest stages of embryogenesis.

See also

• Chimera (genetics)

External links

• Vanishing twin at eMedicine.com
• Wombtwin survivors research and support
• Vanishing twin occurrence in India
• Articles about vanishing twin phenomenon
• LNC Newsletter - Vanishing Twin Syndrome and Fetus Papyraceus
• A review at ^*
• 50 articles about vanishing twin phenomenon in PubMed ^*
• article by Kramer with useful references