Multiple Births: Two, Three, or More Babies

Multiple births are both rare and wonderful, but what goes on before labor and delivery?

We will begin at conception. With multiples, conception can occur in several ways. Technology has increased the likelihood of multiples due to fertility treatments. Natural conception can also occur with many variables.

Regardless of whether the conception takes place under natural circumstances or in vitro fertilization, the number of eggs fertilized will determine what types of twins, triplets, or more that the mother will carry. Identical twins and multiples are formed from a single egg. For this reason, scientists call them monozygotic twins. This occurs about once in every 250 pregnancies. The mother's single egg is fertilized. Within the first fourteen days after conception, the blast cyst divides into separate forms resulting in multiples.

Identical twins are very similar, but will not be exactly alike. It is possible in a few rare cases to have a boy and a girl set of twins. When a mother's egg contains extra DNA material, the fertilized egg can divide into two babies of different sex.

Fraternal siblings are conceived from two or more eggs. they are often referred to as dizygotic twins. It is possible to conceive fraternal, or dizygotic twins, at different times on different days. A single act of intercourse can fertilize the first egg, then a day or two later another egg is released and fertilized by sperm that are still alive from the previous act of intercourse. It is even possible that twins can have different fathers.

Mirror twins are monozygotic twins that separate late, at about day nine, after sides of the cells have been formed. The mirror twins look similar yet different. Each twin is the exact opposite of the other twin. One twin will be right-handed and the other will be left-handed. Even organs like the heart may be on opposite sides of the body.