Essay Example on Conjoined twins CT occurs when twins are joined at Birth

Other cases of pygopagus twins include the Hungarian sisters Helena and Judith 1701 1723 and Bohemian Rosa and Josepha Blazek 1879 1922 Rosa gave birth to a male child which is the only known example of a female CT who had a healthy child according to Guttmacher 1967 as cited by Mutchinick et al One of the most famous cases occurred during the 19th century when PT Barnum coined the term Siamese twins for xiphopagus thoracopagus brothers Chang and Eng who were born in Siam now Thailand They married sisters had 21 children and died at age 61 due to the lack of blood circulating equally Kennedy 2001 In more recent history in 1987 Dr Benjamin Carson Sr received international fame after successfully separating occipital craniopagus twins after a 22 hour surgery The Binder twins of Germany are healthy and alive today He is also known for his 28 hour operation separating craniopagus twins along with two other surgeons More recently Carson aided in an effort to separate adult craniopagus twins in Singapore but was unsuccessful Molnar 2008 According to Reece et al 2012 during fertilization the acrosome in the sperm head releases enzymes which dissolve the egg s protective jelly The acrosomal process allows the sperm to connect with protein receptors in the egg After the sperm enters the egg the egg undergoes the meiosis II to bring the maternal DNA to a haploid state in order for the egg and sperm DNA to fuse and create a diploid state zygote The zygote then undergoes cleavage defined as rapid cell division The first part of cleavage forms a solid ball of stem cells called a morula Through blastulation it hollows out to form the blastula which then undergoes gastrulation to develop the gastrula The gastrula forms the three tissue layers of the body and the placenta develops on the portion of the gastrula known as the trophoblasts The formation of organs organogenesis follows gastrulation During the second and third trimester of pregnancy the fetus grows as the cells undergo mitosis The Washington State Twin Registry states that in 2014 there were over 135 000 births of twins both monozygotic and dizygotic The birth rate for MZ twins is about 4 per 100 births 

Twinning occurs one of two ways A woman releases two eggs which is fertilized by separate sperm resulting in dizygotic twins fraternal If a single fertilized egg divides and separates monozygotic identical twins occur University of Maryland Medical Center There is also a phenomenon in twins known as mirror twins in which identical twins have opposite features In twins there are four following scenarios dichorionic diamniotic with separate placentas 30 40 MZ dichorionic diamniotic with fused placentas monochorionic diamniotic 60 70 MZ and monochorionic monoamniotic as stated by O Brien The chorion is the outermost membrane in embryos and holds the amniotic sac Monochorionic monoamniotic twins can lead to twin to twin transfusion syndrome due to disproportionate blood flow between the two fetuses and is also a characteristic of CT Mutchinick et al 2011 Mutchinick cites a study Levin et al that states that CT originates from a failure in the development of primitive structures The two hypotheses regarding the development of conjoined twins are fission theory and fusion theory There are at least two main hypotheses about the development of conjoined twins Fission theory accounts for all types of CT except parasitic type It suggests that a single fertilized egg does not completely split which causes the embryos to continue development while fused at the unseparated part In contrast fusion theory claims that all types except for parapagus type can be explained by the fusion of two separate embryos Mutchinick