Multiples in pregnancy

Types of Multiples in pregnancy

A pregnancy of two or more fetuses is called a multiple pregnancy. Multiple fetuses can be the same (identical) or different (fraternal). Identical twins or triplets come from a single egg that has been fertilized by one sperm. For unknown reasons, the fertilized egg splits into two or more embryos during the first stage of development. Fraternal multiples come from multiple fertilized eggs.

Some identical multiples share the same placenta. However, they usually grow within separate amniotic sacs in the uterus. In rare cases, identical multiples share one amniotic sac. Fraternal fetuses have separate placentas and amniotic sacs.

Identical multiples:

Are always the same sex and blood type.
Do not always look exactly alike.
One may be right-handed while the other is left-handed.
They are not related to your age, race, or family history of twins.

Fraternal multiples:

Can be of different sexes and have different blood types.
May look very different from one another, with different colored hair and eyes.
They may also look alike, as siblings often do.
Fraternal multiples tend to run in families.


	Types of Twins Fraternal Twins With fraternal twins, the most common type, the mother contributes two eggs that are independently fertilized in the womb by two different sperm cells from the father. They are genetically as similar as any ordinary siblings. Fraternal twins are simply brothers and/or sisters who happen to be the same age. Fraternals are more common for older mothers, with rates doubling over the age of 35. Identical Twins With identical twins, one egg from the mother is fertilized by one sperm from the father, and then very early in development the embryo splits and two fetuses grow. These twins are very similar genetically and they are the same gender. Identical twins appears to be a random event, not a hereditary trait, and is uniformly distributed in all populations around the world. Semi Identical Twins The 'semi-identical' twins are the result of two sperm cells fusing with a single egg, before becoming two embryos. This would result in a set of twins with identical genes from the mother's side, but different ones from the father's side. An embryo created this way doesn't usually survive, but a few cases are known. New Semi Identical Twins These twins are also chimaras, meaning that their cells are not genetically uniform. Each sperm has contributed genes to each child -- a very rare and previously unreported way for twins to come about. Normally, chimeras form essentially when two separate fertilized eggs that would normally make fraternal twins fuse early in development and make a single baby that ends up with a mix of tissues from each egg. Most of the time it goes totally unnoticed, and only shows up either if the two eggs have different genetic genders and the baby ends up with a mix of male and female gonads, or if it happens to be picked up on a genetic test that's done for other reasons (ex. paternity tests).

How Common are Multiples?

There has been an increase in multiple births in recent years. Since 1980, infertility treatment has more than doubled the American twin birth rate. The rate of triplet or more births is now nearly 5 times higher than before infertility treatment was used.

In the year 2000, in the United States, there were:

118,920 Twin Births
6,740 Triplet Births
507 Quadruplet Births
78 Quintuplets & other higher order Births

That is more than a 70 percent increase in the number of twin births from 1980. With just over 4 million births in the United States in 2000, about 3% of babies born in the United States are twins or higher order multiple births (such as triplets), which although not common, does mean that multiples are more common than many people believe.

What are your chance of having more than one baby at a time?

Basically, it is about 3% or 1 in 33. The chance of having 'natural' fraternal twins is only about 1.7% or 1 in 60. The chance of having identical twins has remained steady, and is about 0.4% or 1 in 250. The chances of having twins with the use of fertility treatments can be as high as 20 to 25%.

chance of having 'natural' fraternal twins: 1 in 60
chance of having 'natural' identical twins: 1 in 250
chance of having 'fertility treatment' multiple: 1 in 4
chance of having 'natural' triplets: 1 in 8,100 (only about 30% of triplets are 'natural')
chance of having 'natural' quads: 1 in 729,000 (only about 6% of quads are 'natural')
chance of having 'natural' quints: 1 in 55,000,000

Common factors that increase the chances of conceiving twins.

Fertility Drugs: Taking fertility drugs or undergoing fertility treatments can significantly increase your chances of having twins or another type of multiple birth. In some cases, it can increase your chances of having twins by more than 20%.
Age: Your chances of having twins increases as you grow older. The chance of having twins rises to 4% between the ages of 30 and 34, and to 5% between the ages of 35 and 39.
Family History: Having a maternal history of twins or other multiple births increases your chance of becoming pregnant with twins considerably.
Cultural Background: People of African American descent are more likely to have twins or multiple births. People of Asian or Hispanic descent are less likely to have twins.
Previous Pregnancies: Women who have had four or more previous pregnancies are the most likely to have twins.

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