How is Zygosity of twins determined?

How do you confirm Zygosity?

fraternal twin zygosityToday, expectant parents have the options to know what sex their baby will be or if they are expecting multiples. When it comes to having a birth of twin, zygosity is a concept that is important for parents to understand. It is very unlikely that the word zygosity is not going to come up in everyday conversation, so what is zygosity and furthermore, what is twin zygosity?  

Zygosity refers to the degree of similarity of genetics between DNA sequence  that are inherited from the parents. With twin zygosity, the degree of that genetic similarity within each pair can determine if the “identical” twins are in fact identical from every physical aspect.  Zygosity is a confusing thing for parents of twins and how categorizing twins is done with zygosity. 

What seems to be the old school way of determining if an expectant mother is carrying twins is by ultrasound. However, only way to be certain is by DNA twin zygosity testing  where the following aspects are used:   

  • Ultrasound markers
  • Placental sites
  • Dividing membrane thickness
  • Th lambda sign
  • Fetal gender 
  • Postpartum placental examination
  • Physical similarity questionnaire 
  • Blood type
  • DNA analysis from each twin

Using each of these things, scientists are able to determine twin zygosity with the DNA sample of each twin. With the DNA results, the scientists are able to compare the genetic markers and the sequences of their DNA.

Today though, just as we are able to do our own DNA testing to establish our ancestry,  we are able to purchase home twin zygosity dna kit and perform the testing ourselves.  So, is there a better twin zygosity test better than the others? What is the best twin zygosity test to do at home? However, any expectant mother should seek medical care by a professional and allow them perform any needed twin zygosity testing. 

Twin zygosity is designed to determine if the children of a multiple birth, be it twins, triplets, etc., are fraternal or identical twins genetically. The testing today can be more precise than just 5 years ago, with twin zygosity more distinct and clear by the time the children have reached the age of two. Still yet, the best way twin zygosity testing is still a DNA testing where sample are taken from each twin and each parent. 

There are implications in zygosity testing of multiple pregnancy occasionally. For instance, Twin-to-Twin Transfusion Syndrome and the medical complications that can stem from TTTS.  It cannot be confirmed inconclusively by twin zygosity testing. DNA analysis is needed for doctors to be closer to 100% certain. Where twin zygosity testing comes into play in a helpful manner is for  organ or tissue transplant. 

What is more common dizygotic and monozygotic?

To clarify the difference, monozygotic is identical  twins and dizygotic is fraternal twins, or non-identical.  The monozygotic twins come from a single egg and dizygotic twins are from two egg that were fertilized simultaneously. The birth of dizygotic twins are more common monozygotic twins.

What is the most common twin zygosity, is there are correlation between the mother’s age and the twin zygosity?  The older the mother is when she conceives, the higher the chance of her giving birth to fraternal twin births. When fertility treatments are used to get pregnant, the rate of fraternal twins increase. With various factors considered, fraternal twin  occur in three out of very one hundred births. 

Who carries the twin gene?

Genetic research has found that there is two time great chance of having fraternal twins when there are fraternal twins on the woman’s side by either her mother or sister.  This “twin gene” is caused by hyper ovulation, the tendency for multiple eggs to be released during ovulation. 

Because only the woman ovulates, this connection is valid only for her side of the family. However, the “twin gene” can come from the father and be passed on to the daughter, it increases the daughter’s likely hood of giving birth to fraternal twins.  

What is the rarest type of twins?

twins asleepFraternal twins and identical twins are commonly known when it comes to “twin talk”, but we have learned there are “semi-identical” twins. This third category of twins is ’sesquizygous’, but what is the difference between them and monozygotic (identical) twins?

The monozygotic twins come from one fertilized egg that splits in two, with each part carrying an egg, either two boys or two girls, identical to each other, sharing 00% DNA.

The dizygotic twins are formed when two eggs are fertilized at the same time by two sperm. They are siblings with two unique genetics, sharing only 50% of their DNA.

Semi-identical twins are a rarity, with only two cases of this type of birth being recorded. They share between 50 and 100% of their genomes or the total of their DNA.

How can I tell if I’m an identical twin?

For a person to determine if they have an identical twin, A DNA twin zygosity test would need to be performed. Twin zygosity DNA testing is done by swabbing the inside of each twin’s cheeks and submitting those swabs to a DNA testing center. Want to get started on twin zygosity testing? Call Choice DNA at 800-219-4362.