nspom.org
You were born together, and together you shall
be forevermore... but let there be spaces in your togetherness. And let
the winds of the heavens dance between you.
~ Kahlil Gibran
for login and password
Twin Facts
(Compiled from Various Sources)Each month, we publish a new fun fact in the North Suburban Parents of Multiples (NSPOM) newsletter. We will add these fun facts here each month to keep a running tabulation of these interesting tidbits.
Fun Fact #1: Twin Types Identical twins come from one fertilized egg that splits in two, resulting in same-sex twins who share 100% of their DNA. Fraternal twins result when two separate sperms fertilize two separate eggs. These twins share only 50% of their DNA, just like regular siblings, and can be same gender or boy/girl.
A third type, Polar body twinning, is thought to occur when a single egg splits prior to fertilization and a separate sperm fertilizes each half. These twins share 75% of their DNA, and like fraternal twins, can be same gender or boy/girl.
Fun Fact #2: Twin Symmetry
The incidence of twin types and genders are oddly symmetrical. One third of all twins born are identical, one third are same sex fraternal, and one third are male/female fraternal. Of the identical twins, half are male/male, and half are female/female. Of the same sex fraternal, half are male/male, and half are female/female.
Fun Fact #3: Mirror-Image Twins
Mirror-image twins occur only in identical twins. In approximately 23 percent of identical twins, the fertilized egg splits later than 7 days following conception.
The original right half of the egg becomes one twin and the original left half becomes the other. These twins will often have "mirror images" of their features, such as hair whorls that run clockwise in one and counter-clockwise in the other, a birthmark on the right shoulder of one and the left shoulder of the other, etc. There is no specific test for determining if twins are mirror-image, however. The determination is made by observation only, and the twins must be mono-zygotic, or identical.
This may be a partial explanation for the fact that a little over one third of identical twins are left-handed, double the rate in the general population. In extreme cases, all of the internal organs are reversed in one of the twins, with the heart on the right, the liver on the left, and the appendix on the left.
Fun Fact #4: Do Twins Skip a Generation?
There is no evidence that identical twins run in families. Fraternal twins, produced when the mother's ovaries release more than one egg per cycle, do run in families. A woman can inherit the twin gene directly from her mother, or from her paternal grandmother through her father. This is why many people believe that twins sometimes "skip a generation."
Having twins in the family does not make a man more likely to father twins himself, as his genes have absolutely no influence on whether his wife's ovaries will release multiple eggs. However, a man with fraternal twins in his family can pass the twin gene on to his daughter, increasing her likelihood of releasing multiple eggs and conceiving fraternal twins.
Fun Fact #5: Not Completely Identical?
Identical twins share 100% of their DNA, but they do not have identical fingerprints. Although their fingerprints may be similar, they are still unique to each individual, most likely due to environmental variables within the womb.
Fun Fact #6: Odds of Conceiving Multiples
Without the assistance of fertility treatments, twins occur naturally in 1 out of 80 births; triplets in 1 out of 8000; quadruplets in 1 out of 700,000; and quintuplets in 1 out of 65,610,000.
Those numbers have lowered to 1 in 38 for twins with fertility methods, as well as lowering the numbers for all other multiples. It is estimated that 60% of triplets, 90% of quadruplets, and 99% of quintuplets are conceived due to fertility treatments.
In a recent survey sent to a random sampling of NSPOM members, 36% of respondants conceived their twins spontaneously, while 63% conceived their twins with the assistance of fertility treatments, most commonly IVF.
Symetrical Sleeping Positions?
Some parents notice that, at times, their twins are in mirror-image positions of one another (see picture above). At other times, however, they are perfectly mimicking one another, facing the same direction with head and hands in the same position.