Multiple Births

Multiple births are rare in humans with twins as being the most common form
of this event. Multiple births can arise in many different combinations of ways
but the probability of giving birth to more than one child remains fairly
constant when compared to the entire human race. The chances of multiple births
can also vary from race and genetic background. Scientist and researchers do
not know what the exact cause of these variations is but many of them feel that
it is caused by hormone differences between different racial groups and/or the
difference in social class.
The prenatal and infant mortality is much higher in multiple pregnancies
than in pregnancies that only involves one child. The danger of premature birth
also increased with the higher number of offspring that are involved. In many
multiple births, not all of the children survived to childhood or were born dead.
Through the advances in technology, the survival rate of infants born in a
multiple pregnancy has increased. The first quintuplets, five babies born in a
single pregnancy, to survive in medical history were the Dionne quintuplets.
The use of drugs that treat female sterility, or fertility drugs, may
increase the chances of giving birth to multiple children. These drugs cause
the ovaries to release an egg once a month but in some cases they release more
than one egg, sometimes releasing several at a time, increasing the chances of a
multiple birth. The drug clomiphene citrate is one of the most widely taken
fertility drug and has resulted in the birth of twins about once in every twelve
births, much greater than the chances of the birth of natural twins.
Twins are the most common form of a multiple pregnancy. About one in
eighty-seven births result in the birth of twins. Twins can be fraternal, also
known as dizygotic twins, or identical, also called monozygotic twins, with the
birth of identical twins being the rarest, occurring about four times in every
thousand births, about one-forth as often as the birth of fraternal twins. This
ratio of the birth of twins to the total number of births remains fairly
constant but the birth of fraternal twins can alter greatly. Fraternal twins
are most common among black African followed by people of European origin.
Asian races originating from the orient are the least likely to give birth to
fraternal twins.
The birth of twins can occur in two different ways, the fertilization of
a single egg or the fertilization of two eggs. In the case of dizygotic twins,
the woman\'s ovaries release two eggs about the same time instead of one, with
each being fertilized by the male\'s sperm, fraternal twins begin to develop.
The two zygotes develop differently, each having a different genetic coding.
They can be both boys, both girls, or a single boy and a single girl. Because
each embryo develops on its own from different genetic characteristics,
dizygotic twins resemble family characteristics as do brother and sister.
The birth of monozygotic twins takes place much differently than do the
births of fraternal twins. Identical twins originate from a single egg,
fertilized similarly to that of a single pregnancy. A change transpires early
in the pregnancy that causes the development of identical twins. The change
from a single birth to the birth of monozygotic twins occurs when the zygote
ruptures into two separate structures. These two parts begin to develop into
individual fetuses, sharing a similar genetic code and developing in a similar
manner. Identical twins are of the same sex, resemble each other very closely,
and have similar fingerprints and blood types.
Scientists also believe that Siamese twins, also known as conjoined
twins, develop in a similar fashion as do monozygotic twins. Siamese twins are
identical twins with the difference that the zygote did not divide completely
during their development. Such twins are usually joined at the hip, chest,
abdomen, buttocks, or head. With current monitoring equipment, conjoined twins
can be detected maturing in the mother and during birth a Cesarean section is
sometimes needed to deliver the children safely. Separation of the twins
sometimes leads to the death of one or both of the twins. This births are a
rare event, occurring only about once in every fifty-thousand births.
Other forms of multiple births such as triplets, quadruplets and
quintuplets, occur very similarly to the birth of twins. Births of triplets are
rarer than the birth of twins, occurring approximately once in every seven-
thousand nine-hundred births. The birth of triplets can occur in a combination
of ways. If the zygote divides into three separate structures in the early
stages of development,