The number of women having multiple births in the USA has increased year on year since 1980. In 1980, 1 in 53 babies was a twin; whereas in 2009, 1 in 30 babies was a twin . This represents a 76% increase in the twin birth rate over 30 years.
No-one is certain why multiple births are increasing, but several factors play a role:
- The increased use of conception techniques, such as IVF. According to statistics published in 2013, around 40% of all IVF pregnancies in the USA resulted in multiple births.
- Mothers waiting later to start their families. Women aged 45 and over are most likely to have a multiple birth.
- Maternal history. A mother is more likely to have multiple births if there is a history of multiple pregnancies in her family.
- An increase in obese mothers. Research has shown that mothers with an increasing body mass index (BMI) can lead to more multiple births.
Whether or not the twins, triplets, quadruplets and higher multiple babies are identical depends on how the babies were formed. Non-identical siblings are the result of separate fertilized eggs. These babies are no more alike than any other brothers or sisters, and may be both male, both female, or one of each. They share DNA in common as in the case of siblings from different births.
Identical siblings are formed from a single fertilized egg, which went on to split into separate embryos. This means their DNA is exactly the same.
What does an identical twin test entail?
An easy way to determine whether multiple children from the same birth are genetically identical or not is by Twin testing (also known as zygosity testing). The test involves analyzing tiny amounts of DNA from inside each sibling’s mouth. Specific markers present in repeat sections of DNA are examined. These Short Tandem Repeat (STR) loci include the Amelogenin (gender) locus. The DNA seen at each of these STR loci is compared between the tested individuals; identical siblings will share the same DNA profile whereas non-identical siblings will have different DNA profiles.
An increasing and novel use of an identical twin test is to use the DNA profile to create a unique gift for new parents, their children, and friends and family. The DNA profile can also be made into exclusive artwork. National Center for Health Statistics. Three Decades of Twin Births in the United States, 1980–2009. https://www.cdc.gov/nchs/data/databriefs/db80.htm