The Vanishing Twin

Abstract

In general, it has not been recognized that many twin or multiple gestations are lost in utero early in pregnancy. Until the advent of ultrasound, the ability to document early human fetal loss in multiple gestation was difficult. However, recent reports of serial ultrasound examinations of pregnant women have documented the "disappearance" of at least one of two gestational rings. Furthermore, the number of twins observed at delivery was significantly less than the number of twin conceptions originally identified by ultrasound during the first trimester. These observations led to the concept of the "vanishing twin" [8,10,13,15,17,20,22,35,41].In order to obtain reference and personal data on this subject, we reviewed the literature and corresponded with members of the International Society for Twin Studies and obstetricians affiliated with Northwestern University Medical School, Chicago, Illinois. The nine studies that have documented this phenomenon cite "disappearance" rates ranging from 0% to 78%, depending on patient population and timing of ultrasonography [8,10,13,15,17,20,22,35,41]. Several explanations are offered: physiological mechanisms of "disappearance" (resorption or formation of a blighted ovum or fetus papyraceus), artifactual error, incomplete scanning technique, and poor quality ultrasound equipment. The only complication thus far associated with "disappearance" of a fetus is slight vaginal bleeding.

Monozygotic twinning: an evolutionary hypothesis.

“…However, such events might be hard to detect because they are expected to occur soon after fertilization, before implantation, and the final clutch size and sex ratio would go unaltered unless twinning were sex-biased (see below). The results of this mechanism would be similar to the "vanishing twin" phenomenon in humans (22) in which the prenatal twinning rate appears to be considerably higher than the rate observed at birth. When parents reduced investment without clutch reduction (model 2), twinning alleles did not always go to fixation or even succeed in the model, especially in large clutches.…”

Genetic and environmental influences on human dental variation: A critical evaluation of studies involving twins

“…Twinning has been associated with a high peri-natal mortality rate 8 and MZ twins display a higher prevalence of congenital abnormalities, many of which appear to be related to failure of bilateral structures to fuse properly during development 9 . Although some claim that the potentially harmful effects of twin gestation have been exaggerated, 10 a large percentage of twins may not develop past 16 weeks post-conception, leading some researchers to refer to a ‘vanishing twin’ syndrome 11 …”

Screening and Invasive Testing in Twins

“…The arrest of development and the subsequent reabsorption of an embryo may occur in early gestational life and is termed “vanishing embryo” syndrome [ 13 ]. Regarding the frequency of this phenomenon, very different figures are employed to define the pregnancy, with estimations based per patient, per gestational sac, per embryo or cardiac activity [ 14 ].…”