About Identical Twins (Monozygotic Twins)

Identical twins, those with identical genes, are formed when a fertilized egg splits into two equal halves. The incidence of identical twins is about one in every 250 live births.

Identical twins are always the same sex. They also tend to have identical features although they can look very different at birth if they were subject to an unequal blood supply in the uterus.

By age two, though, most identical twins will have the same eye color, hair color and texture, and height and weight. It's interesting to note though that while their handprints (and fingerprints) and footprints are similar, they are not identical.

Mirror Twins

About one quarter of identical twins are "mirror twins." This means that certain identical features are on the opposite side--like a mirror image. For instance, one twin is right-handed and the other is left-handed. Some mirror twins might have internal organs on the opposite side of the body (most often seen with the heart). Mirror twinning usually occurs in twins who separated late.

How do you determine if twins are identical?

The zygosity--whether your twins are identical or fraternal--can be determined before birth through genetic tests like amniocentisis or chorionic villus sampling. Your doctor can tell you more about these tests and the risks and/or benefits associated with them.

Often parents of twins are told that they do not have identical twins when two placentas are present. While the presence of one placenta is proof that you are carrying identical twins, some identical twins are formed in the womb with separate placentas. This normally happens when the division of the egg happens within the first four days of fertilization.

If the zygosity of your twins isn't clear at birth, you can ask your doctor to send a sample of the placenta for testing. Later, if you didn't have testing done at birth, you can have an DNA fingerprinting test done to determine your twins' zygosity for a relatively low cost. Talk to your doctor about your options

Or are they fraternal twins?

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Identical Twin Photos

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Drew & Josh Not rated yet
I found out I was pregnant at exactly the same time as my first pregnancy (I found out through a home pregnancy test on Thanksgiving both times; my first …

Destruction of the Temple Not rated yet
You leave your kids alone at Angkor Wat, and look what happens...

OK, truth be told, Micah and Malachi Larson (aka "This One" and "That One") didn't …

Everlynn & Vivian Not rated yet
This picture is NOT photoshopped! They were 7 months and apparently the flash scared Everlynn and Vivian thought it was funny;) We love this one!!

Although... …

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