A chimera may be intersex, composed of cells from a male twin and a female twin. In one case DNA tests determined that a woman, Lydia Fairchild, mystifyingly, was not the mother of two of her three children; she was found to be a chimera, and the two children were conceived from eggs derived from cells of their mothers twin. Parasitic twins
Sometimes one twin fetus will fail to develop completely and continue to cause problems for its surviving twin. One fetus acts as a parasite towards the other. Sometimes the parasitic twin becomes an almost indistinguishable part of the other, and sometimes this needs to be treated medically. Partial molar twins
A very rare type of parasitic twinning is one where a single viable twin is endangered when the other zygote becomes cancerous, or "molar". This means that the molar zygotes cellular division continues unchecked, resulting in a cancerous growth that overtakes the viable fetus. Typically, this results when one twin has either triploidy or complete paternal uniparental disomy, resulting in little or no fetus and a cancerous, overgrown placenta, resembling a bunch of grapes. Miscarried twin
Occasionally, a woman will suffer a miscarriage early in pregnancy, yet the pregnancy will continue; one twin was miscarried but the other was able to be carried to term. This occurrence is similar to the vanishing twin syndrome, but typically occurs later, as the twin is not reabsorbed. Low birth weight
It is very common for twins to be born at a low birth weight.
Retrieved 2008-10-02. "TWINS Guide to the First Year" (PDF). TWINS Magazine. Fort Collins, Colorado. 2008. Archived from the original (PDF) on 2008-10-30. Retrieved 2008-10-06. Samson, Jennifer. "Facts About Multiples: An Encyclopedia of Multiple Birth Records". Archived from the original on 2009-10-15. Retrieved 2008-10-18. Taylor, Ally. "Twin Zygosity Test for Dichorionic Diamniotic (Di/Di) Twins! Zygosity Reveal". Retrieved 2018-03-30. Am J Med Genet C Semin Med Genet. 2009 May 15;151C(2):136-41. Not really identical: epigenetic differences in monozygotic twins and implications for twin studies in psychiatry. Haque FN, Gottesman II, Wong AH. Twin brothers promoted as Majors General together. Seneviratne brothers, who are twins and joined the Army on a same day, were promoted to the rank of Major General, again on the same day. == External links ==