First discovered in 1945, vanishing twin syndrome (VTS) is just one of many types of miscarriage of multiples (i.e., twins, triplets, and higher-order multiples) that does not always yield a complete, spontaneous abortion (i.e., excretion of deceased fetal remains). It is estimated to naturally occur in up to 36% of twin, ~50% of triplet pregnancies, and ~20-30% of pregnancies conceived with reproductive assistance [1-2]. VTS can result in three general outcomes:

1) No visible remains of the twin or multiples, which is the most common outcome

2) Some visible remains, such as a small cystic area in the uterus or a blighted ovum

3) Fetal remains visible throughout pregnancy or at delivery, usually appearing as a thin, calcified fetus (fetus papyraceus) [1].

The outcomes of VTS can vary due to a number of factors, including but not limited to the timing of death in gestation, cause of death, and the type of multiples [1]. VTS most often occurs in the first trimester, often due to chromosomal abnormalities or other early developmental issues [1]. However, it can also occur later in pregnancy, where outcomes may be more complicated for the surviving baby or babies [1]. 

VTS is speculated to occur primarily due to chromosomal abnormalities, but further research is needed to understand this and quantify a more accurate rate of occurrence of VTS [1]. This syndrome naturally occurs in more than 50% of triplet pregnancies and more than 35% of twin pregnancies [1].

Diagnosing VTS comes with several hurdles. The first is timing: early ultrasounds aren’t always available, and by the time most people get scanned, the evidence of a vanished twin may no longer be visible. Additionally, guidelines for diagnosis vary and in some regions are lacking entirely [3]. 

Perhaps most concerning is that families often are not told about VTS, either because providers do not think it is significant or because the communication is difficult or unclear [4]. These gaps create confusion and sometimes silence around what the research has shown many patients feel is an impactful event that can have lasting physiological and psychological consequences on families and surviving children.