If you've ever seen two younger siblings easily converse in complete gibberish, you've probably witnessed idioglossi, a self-contained language often created and shared between twins. With the increasing use of ultrasound, twins have been detected early in pregnancy but "disappeared" on later ultrasounds. This phenomenon has been called missing twin syndrome and the cause is not yet well understood. They have been studied, analyzed and written about for a long time across cultures, but there is still much to learn about multiple twins. Monozygotic twins are also called identical twins. They occur when a fertilized egg divides and develops into two fetuses. Fetuses generally share the same placenta. Identical twins have the same genes, so they usually look the same and are the same sex. Dizygotic twins are also called fraternal twins. They develop when two separate eggs are fertilized by two different sperm. Each twin usually has its own placenta. Fraternal twins (like other siblings) share about 50% of their genes, so they can be different sexes. They are generally no more alike than brothers or sisters born from different pregnancies. Fraternal twins are more common than identical twins. There are also rare types of twins. These categories include: mirror image twins, polar body twins, or conjoined twins. Mirror-image twins occur when about 23 percent of identical twins have an egg that divides later than usual, most often on the seventh day or beyond. The original right half of the egg becomes one individual and the original left half becomes the other. For example, one will be right-handed, the other left-handed. The determination is made purely by observation and it only occurs in the middle of a paper...... years and they are currently living. Multiples are different, distinct, special and fascinating. Triplets and other higher order multiples are not as common as twins. These can result from three or more eggs being fertilized, one egg being split twice (or more), or a combination of both. A set of higher-order multiples may contain all fraternal siblings or a combination of identical and fraternal siblings. Between 1980 and 1998, the rate of triplets and higher order multiples in the United States increased by 70%. Since then, the rate has stabilized. It is estimated that a woman has a one in 64 million chance of conceiving identical quadruplets. The record number of fetuses in the human uterus at one time is 15. Common complications of multiple pregnancy are premature birth, low birth weight, twin transfusion syndrome (TTTS), preeclampsia and gestational diabetes..