The world of multiples is a complex one. We may know about Fraternal and Identical twins but what we are told may be an oversimplification of the mystery of twins. With advancements in technology, In Vitro Fertilisation (IVF), and a better understanding of genetics, science is opening doors into realms we never knew existed before. So yes, the plot thickens. Currently, it is said that there are actually 11 types of twins (and we thought there were only two!). These variations range from Semi-Identical Twins to Mirror Image Twins, to Chimera \u00a0Hermaphrodite Twins to Mosaic Turner Twins, to Polar Body Twins to Mixed Chromosome Twins to Superfecundation and Superfetation and even Parasitic and Acardiac Twins. There may be more to this growing list of twins. Two cases of Semi Identical Twins have been reported to date. 1) The Journal of Human Genetics documented the first case in the USA in 2007. 2) The New Scientist reported a second case in Australia in 2014. Semi Identical Twinning happens when two sperm from the same man simultaneously fertilises one egg. The egg splits resulting in each twin getting 100% of DNA from mother but only 75% to 78% from each sperm making them half fraternal and half identical twins. (Image Credit: ListVerse) So Many Unanswered Questions But why does an egg split to form separate human beings? Why does it sometimes merge back after fertilsation, or drop a chromosome halfway through or fuse into one egg from two separate eggs? These and more are some of the questions science attempts to answer about the convoluted twists and turns the human reproductive process may take when it creates new human beings. For the meantime, however, we shall attempt to answer three of the more mind-boggling questions. These are in relation to the rare occurrences of superfecundation and superfetation. Questions & Answers 1. If a Woman is Pregnant with Twins, could these Twins be Fathered by Two Different Men? The answer to that is Yes. This is due to an ovulation phenomenon called Superfecundation. It means a second ovum released during the woman\u2019s same oestrus cycle is fertilised as a result of a separate act of sexual intercourse. The term superfecundation is derived from the word \u201cfecund\u201d \u2500 meaning the ability to produce offspring. Heteropaternal superfecundation occurs when two different males father fraternal twins. It has been speculated that superfecundation by the same father is a common occurrence but no one has proven it has occurred until a case is reported by the family or father that the offsprings look very different from each other and a DNA test is conducted. Superfecundation most commonly happens within hours or days of the first instance of fertilisation when ova is released during the same cycle. There is a small window of time when eggs are able to be fertilised. Sperm cells can live inside a female\u2019s body for four to five days. Once ovulation occurs, the egg remains viable for 12\u201348 hours before it begins to disintegrate. Thus, the fertile period can span five to seven days. If the woman has sex with another man within that time frame, then the second egg that somehow did not get fertilised in the first round, gets fertilised this time around, she will bear twins belonging to different men. Reported Cases of Heteropaternal Superfecundation\u00a0 \tAccording to Information Nigeria, a Turkish man divorced his wife after DNA tests showed he was the father of only one of their twin boys. The Turkish daily newspaper Sabah reported in 2010, the security guard from Istanbul, identified only as AK, had DNA tests done on the three-year-olds after becoming suspicious his wife had been unfaithful. The tests established with a 99.99% certainty that the man was the father of only one of the boys. \tIn 2016, a pair of fraternal twins born in Vietnam have been found to have different fathers. The family decided to have the two-year-olds tested when family members noted that one twin had thick wavy hair, while the other had thin straight hair. DNA tests were performed on the twins at the Center for Genetic Analysis and Technologies in Hanoi and Le Dinh Luong, president of the Genetic Association of Vietnam confirmed that the twins do in fact have two different fathers. Here is a video of the latest case of Heteropaternal Superfecundation. In March 2019, it was reported that a Chinese woman had twins from two different fathers. https:\/\/www.youtube.com\/watch?vlD9NI-Jme-A 2. Can a Woman get Pregnant with a Second Baby while already Pregnant with a First? The answer to the question is Yes again! It is possible to get pregnant once you're already pregnant because of superfetation. \u00a0Here is how it happens. In biology class back in school, you might have learnt that pregnancy occurs when an ovum (egg) is fertilised by sperm. The fertilised ovum then implants itself in a woman\u2019s uterus and the woman is officially pregnant. For a second pregnancy to happen, another completely different ovum needs to be fertilised and then implanted separately in the womb \u2500 \u201croughly two to four weeks\u201d according to a study published in NCBI \u2500\u00a0 after the first pregnancy. However, three unlikely events must also take place: 1. She must ovulate while pregnant. This is not supposed to happen because hormonal changes from the ongoing pregnancy stops her ovaries from ovulating or releasing more eggs to be fertilised. 2 The second ovum needs to be fertilised by a sperm cell. This is difficult as the elevated pregnancy hormones have triggered the formation of a mucus plug in the cervix, thus blocking sperm from swimming up to the uterus should she have sexual intercourse. 3. The fertilised egg needs to implant in an already pregnant uterus.\u00a0This is also difficult because implantation requires the release of certain hormones that wouldn\u2019t be released if a woman was already pregnant. The wall of the uterus is already thickened from the on-going pregnancy and there is also the issue of having enough space in the uterus to implant another embryo. How can this be possible? IVF plays a role here. Of the few cases of superfetation reported in medical literatures, most of the women were discovered to be undergoing fertility treatments. \u00a0However, sometimes getting pregnant while being pregnant may not be due to IVF as can be seen in this video. https:\/\/www.youtube.com\/watch?vqogkL-McP4E Superfetation twins usually would have different due dates.\u00a0 Or, one twin when delivered would be smaller than the other due to not having reached its full term at the time of delivery. It was reported in Time Magazine in 2009, that Julia Grovenburg became pregnant twice, two weeks apart. She gave birth to twins (a boy and a girl) on Dec 24 and on January 10 the following year. Superfetation is not actually a new phenomenon as it happens commonly in animals but in human beings, there have only been around 10 recorded cases to date. 3. Can Twins of Bi-Racial Marriages come out as Different Races? This question gets its answer from genetics rather than the process of ovulation. As can be seen from the pictures and video below \u2500 can twins of mixed parentage come out with contrasting skin tones? \u2500 the answer is Yes and quite frequently too. Wikipedia has the scientific explanation. Three different sets of bi-racial twins from three different mixed race families exhibiting contrasting skin colours (Image Credit: You Tube) Mixed twins\u00a0are\u00a0fraternal twins\u00a0born to\u00a0multiracial\u00a0families that differ in\u00a0skin colour\u00a0and other racial\u00a0traits and features. From a biological standpoint, the differences in these fraternal twins from two biracial parents are not surprising. In\u00a0humans, a relatively small number of\u00a0genes\u00a0are thought to be responsible for skin colour. Different alleles (variant form of a gene) can result in differences in the melanin found within the skin. Within some groups are high frequencies of dark skin alleles, while others have high frequencies of light skin alleles. The parents of such twins, who are typically of mixed race, have a combination of alleles for light and dark skin in their\u00a0genome. https:\/\/www.youtube.com\/watch?vJIUK2KSbvvI For more fascinating insights on singles and multiples, visit Motherhood.com.my.