PEOPLE - Top 10 Different Types of Twins

Article by Parulkhani

The world is full of all the miracles and extraordinary things,and these extraordinary miracles is what makes the world complete. Let us look at these miracles, in the context of a birth of a newborn. There are different kinds of babies that are born today- Twins, triplets, quadruplets, conjoined, parasitic, semi-identical, etc. A twin is one or two baby or an offspring produced in the same pregnancy. Multiple births are basically rare in humans and can arise in different combinations, and it can vary from race to the genetic background. Twinning not only means looking alike, there a many forms of twins with different ages, gender, race, etc. According to the studies, these variations are caused by different racial groups or social class rather than hormone differences. The odds of having multiple twins is almost 3 in 1,000 and their birth rates is about 32.2 in 1,000 and the identical twinning is not usually influenced by fertility upgrading treatments like drugs or in vitro. Here is the top ten list of twin birth rarities.

10. Conjoined Twins

Conjoined Twins are identical twins which do not separate fully from each other due to incomplete division of the ovum,and their bodies are joined together at birth. Almost have are stillborn and some pairs have abnormalities and this condition is mostly found among females. These twins will be connected at certain points of body and share a common tissue, organ, chorion, placenta, amniotic sac or limbs.  The origin of conjoined twins is explained with two theories – fission and fusion. In the fission, the fertilized egg splits partially and in fusion, the egg fully separates but the stem cells fuse the twins together. ‘Chang and Eng Bunker’ is the most famous pair of conjoined twins and due to rarity of this condition, ‘Siamese Twins’ is used as the synonym for conjoined twins. One more important fact about these twins, that is studied is that they cannot be of different genders. These twins are either two girls or two boys. This conjoined condition occurs 1 in 50,000 human pregnancies.

9. Half Identical Twins

Half identical twins or semi identical twins are a very rare formation of twinning in which twins inherit same genes from mother but different genes from father. These twins are half identical, they are not 100% match DNA but these twins are very much alike. They can be of two types- Monozygotic(identical) which means they develop from two zygote and then split into two embryos or Dizygotic(fraternal) which means they develop from two eggs, inseminated by separate sperm cell. A single fetus is known as ‘singleton’ and and offspring of multiple birth is ‘multiple’.

8. Monozygotic Twins

Monozygotic twins means mono(single) zygote(fertilized egg). Monozygotic twins are formed with one egg and one sperm forms a zygote and then splits into two embryos. These embryos then forms separate fetus. These are also called identical twins because they share identical genes, but they are not perfectly identical, although can be very alike. These twins have identical DNA and the differences and variations are caused by environmental factors. It means that the monozygotic twins are of the same sex, same physical traits and even almost similar personalities. Monozygotic twins also share the same placenta but have separate amniotic sacs. These twins are also called ‘maternal’ twins. This twinning occur at the rate of about 3 in every 1000 human deliveries worldwide.

7. Dizygotic Twins

Dizygotic means Di(two) zygote(fertilized egg). these twins are formed when two eggs are fused and fertilized by two separate sperms producing two separate zygotes. Usually women only release one egg in an ovulation cycle but sometimes multiple eggs are released leading to dizygotic twins. Dizygotic twins do not share same genes. They occur when two or more eggs are released in one cycle and if both of them are fertilized, they result in dizygotic twins. They have very slight chances of having the same chromosome profile. They can be of the same sex or different sex too. These twins have their own placentas and amniotic sacs, and this is also known as being ‘dichorionic-diamniotic (Di-Di)’. If the Di-Di is low, they have the lowest mortality rate of all twins. These are also called as ‘non-identical’ twins or ‘fraternal’ twins.

6. Mirror Image Twins

Mirror image twins are formed when the fertilized eggs separate late(around 9-12 days) in the embryonic stage different from the normal time. These twins are genetically identical but have small mirror image differences. They have the same DNA and some of their body parts are mirrored. These twins could have reversed asymmetry such as opposite handed, mirror image dental structure, personality traits associated to right-brain or left-brain. These twins look similar but resemble even stronger when stand facing each other just like a mirror. They appear as exact reflections of each other and maybe right and left-handed, have birth-marks on the opposite side of the body. If these twins split later than the above time period, then these twins may be conjoined.

5. Parasitic Twins

Parasitic twins are also known as asymmetrical or unequal conjoined twins because they are asymmetric conjoined identical in which the tissues of the defective twin (parasite) are dependent on the cardiovascular system of the other twin. This condition occurs when an underdeveloped twin is attached to any body parts of the other twin as it develops and is birthed. The parasitic twin becomes an indistinguishable part of the other baby and sometimes it needs to treated and removed surgically.The twin embryo starts developing, but the pair does not separate properly. The parasitic twin syndrome is known as ‘conjoined twin’ syndrome or ‘two-headed’ syndrome.

4. Superfetation twins

Superfetation is a term used in which a fetus is formed while the other fetus is already in the uterus. It happens when two menstrual cycle releases eggs different from normal zygotic twins where multiple ova are released in a single cycle. When two separate occurrence of fertilization takes place during the same cycle, it is called ‘superfecundation’. Studies say that superfetation is common among animals but rare in human beings. In mammals, it occurs only when there are two uteri and the risk with superfetation is that the second baby is said to be born prematurely or with disorders with the risk of lung problems.

3. Heteropaternal Superfecundation twins- Twins with different Fathers

Fraternal twins are formed by hyperovulation that releases multiple eggs in one cycle. Superfecundation explains a situation in which eggs are fertilized by sperm of different male partners. The second ova should be conceived within hours or few days past the first conception. The eggs live upto forty eight hours after they are released to the uterus. Heteropaternal superfecundation is common in dogs and cats.

2. Twins with Different Birthdays

Most twins share the same birthday as they are born together. But there are cases when twins share different birthdays and that happens when a delayed interval birth takes place when one kid or a multiple is delivered prematurely, but the doctors keep the remaining twin in the womb to grow and develop naturally and helps to halt labor. So, some of these twins or triplets or more are born days, weeks or even month apart having different birth dates. Some twins are also born in the middle of the night and so they may arrive on different dates having different birthdays.

1. Twins of Different Race

Twins of the different race are produced if the parents are of mixed race, and when their sperms and eggs are fused and fertilized gives a mixture of genetic codes for black and white skin. Their skin color is determined up to seven different genes working together. The chance of a mixed race couple of having twins of different colors are a million to one. If the twins are inherited from mixed race parents, one can be white, fair-haired and light skin and the other can be black and have dark hair.