Types of Twins

Types of Twins

• Identical and Fraternal & More

Identical and fraternal multiples are two of the most commonly known types of twins but they are not the only types of twins.

Monozygotic and Dizygotic

Identical

Identical twins also known as monozygotic occur when one fertilized zygote (egg) splits into two separate embryos. They have almost perfectly match DNA and look very alike, though they can also look quite different especially if TTTS was a factor during pregnancy. Different birth weights can result in being mistaken for fraternal Multiples. A DNA test can be done to confirm whether or not your little ones are identical or fraternal.

Fraternal

Fraternal twins also known as dizygotic happens when two eggs have been realised by the mother and then fertilized by two sperm. They can be two boys, two girls or one of each a boy and a girl. 

Fraternal twining is are hereditary and have their very own placenta, though sometimes they can fuse together. Dizygotic multiples are the most common of all twining.

Other Types of Twins 

Mirror Image

Mirror image twins form the same way as monozygotic, splitting more than 7 days after conception. About 25% of all identical twins are mirror image. This means one may be right handed while the other is left handed, their hair may have swirls growing in the opposite directions, identical birthmarks on opposite sides or the body and even suck on different thumbs. You could say it’s like looking in a mirror.

Conjoined

Conjoined Twins are also monozygotic (identical) and are also known as Siamese Twins. This occurs whilst in the womb and they do not completely separate, they can share organs, tissue or even limbs. Surgery to separate the conjoined multiples has been successful but brings many risks. 

More Facts About Conjoined Twins 

Here is some information about conjoined twins, which has always been a medical wonder and curiosity by all.

From how often this phenomenon occurs, statistics and history. What would you like to know?

• They are always identical twins, which also means they are the same sex. They are developed from one fertilized egg which doesn’t complete the split.
• Conjoined (aka Siamese) twins are a very rare complication with identical twin pregnancies, occurring in about 1 in every 200,000 pregnancies.
• It is 70% more likely that conjoined twins will be female. Female babies are much stronger than male babes. Although males twins are more likely to conjoin the female sets are more likely to survive.
• The earliest documented twins who were conjoined are brothers from Armenia and dates back to 945 AD. The brothers were connected the waist to the abdomen. During an attempt to separate the boys one dies and the other died 3 days later.
• Another set of twins who were connected at the hip and shoulder, are considered one of the more famous documented twins, Mary and Eliza Chulkhurst. They were from Kent, England and became known as the Biddenden Maids. They lived until the age of 34.
• The phrase Siamese Twins come from the famous twins, Chang and Eng Bunker from Thailand (which was called Siam at the time). The brothers became famous before marrying and settling down in the United States. The expression Siamese Twins now-a-days is viewed as inappropriate.
• About 50% of conjoined (siamese) twins are stillborn and 35% only survive for the first 24 hours. And 5 – 25% of all will survive.
• In modern times, the first conjoined two (who were conjoined at the lower back) that were separated successfully was Caroline and Catherine Mouton from Louisiana. Born in 1953 and at only 8 days old they were separated with both girls surviving. The actual first ever successful separation is said to be in the year 1689 of females joined by a ligament only 4.7” wide.
• There is no documentation to suggest conjoined triplets or more have ever existed. The possibility of a parasitic twin along with conjoined would be more likely.
• This is not preventable and there is nothing the mother has done wrong.
• Joined Twins are born all throughout the world and are not limited to any racial or ethnic groups.

Polar Body – Half Identical

Though there is no real test to confirm polar body twinning this refers to an egg splitting before fertilization then each half will be connected with two different sperm. Half multiples look very alike but their DNA is not matching.

Twins Conceived Separately

Very rarely multiples can be conceived at different times. During early pregnancy, an egg can be released which could be fertilized resulting in fraternal twins, this process is called superfecundation.

Semi-Identical Multiples

This occurs when two sperm fertilize one egg which then later splits. These types of twins were acknowledged in 2007 in a pair of 3 year old multiples.

Twins who have Different Fathers

When a woman releases more than one egg and has different sexual partners who both fertilize an egg each. This is extremely rare some say only occurring as little as one in a million. The term used is heteropaternal superfecundation.

Twins of Different Races

These types of twins are dizygotic of different racial characteristics, known by the term heteropaternal superfecundation. In the UK two bi-racial parents conceived fraternal twin girls, one having fair hair, skin and blue eyes (like their mother) while the other has dark hair, eyes and skin (like their father). The one in a million family seven years later fell pregnant again, having twins once again and the one in a million occurrence was repeated with lovely girls also having different skin tones. In another case this was due to a lab mix up during IVF.

Boy/Girl Identical (monozygotic) Multiples

Though identical's are thought to be always the same gender, in extremely rare cases boy/girl monozygotic twins is a possibility. This happens when there is a genetic mutation in male babies, one baby loses a Y chromosome which then develops as female. A chromosome disorder known as Turner’s Syndrome would affect the female, symptoms can include extremely short stature, puberty issues, hearing problems among others.

Parasitic Twins

This is when conjoined twins develop disproportionately with the stronger baby supporting the fetus fetu. A parasitic twin can consist of extra limbs or abnormal cell growth that grows inside the other stronger twin.

Multiples can Have Different Birthdays

Let’s say baby number one is born at 11:55pm and the second twin is born at 12:01am the next day, this is the most common explanation for different birthdays.

They could even be born in different years, if you had twin A on December 31st the other could be born on the 1st of January the next year.