1999-05-27-18 Vanishing twin © Gonçalves www.thefetus.net/
Luís Flávio de Andrade Gonçalves, MD1, Sandra Rejane Silva, MD2, Philippe Jeanty, MD, PhD3
 Florianopolis, SC Brazil,  Sao Paulo – SP  Nashville, TN email@example.com
Adapted and reproduced with permission from TKI Medcon Inc. http:/www.tki.com/
First trimester loss of a member of a twin gestation.
Small gestational sac with a fetus whose development lags compared to the other fetus. No fetal heart activity can be detected. The spectrum varies from a crescent-shaped sac adjacent to a normal early gestation (up to 10-14 weeks) to a well-formed but dead fetus (fetus papyraceus). Early vanishing twins should be distinguished from implantation bleeds that are not surrounded by a trophoblastic ring.
An ill-defined gestational sac that could easily appear to be an implantation bleed, although some agonal flow still go to the embryo.
The five image above are from a triplet pregnancy (trichorionic). On the first image the smallest gestational sac is visible. It contains no embryo. The left sac contains an embryo with no heart beat. The lower sac contains a live embryo.
Dichorionic diamniotic gestational sacs. On the first image, there is no evidence of an embryo, the second image obtained a week later, demonstrates normal growth one one embryo and elimination of the other sac.
At 16 weeks, the sac of a vanishing twins can sometimes still be visible.
17-weeks. A fetus papyraceus (first image) and the normal co-twin.
The differential diagnosis includes implantation bleeds in the early pregnancy and chorioangioma as well placental cysts after the second trimester. Chorioangioma is the most important entity in the differential diagnosis because of its known relationship to nonimmune hydrops as well as preeclampsia. The lack of blood flow on color Doppler, excludes the diagnosis of chorioangioma.
Fetus papyraceus. This is a macerated fetus delivered with a normal co-twin, and usually embedded in the placental membranes.
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