Twins - how can this be?

What are the twins?What are the twins?

twinstwins are two are two offspring resulting from the resulting from the same same pregnancy, usually , usually born in close in close succession.succession.

They can be the same or different sex. They can be the same or different sex.

Three Types of twinsThree Types of twins

Types of twins

identicalidentical twinstwins fraternal twinsfraternal twinsConjoined twinsConjoined twins

stages of twin formationstages of twin formation

As off springs reproduced by fertilization As off springs reproduced by fertilization the fertilized egg, now called a the fertilized egg, now called a zygotezygote divides divides

one time, resulting in two cells.one time, resulting in two cells. By the sixth day after fertilization, the By the sixth day after fertilization, the zygotezygote

implants itself in the uterine wall and continues implants itself in the uterine wall and continues to develop for nine months. to develop for nine months.

after implantation, the developing baby is called after implantation, the developing baby is called an an embryoembryo. .

Around week nine of development, it is called a Around week nine of development, it is called a fetusfetus

Now we know and twins are formedNow we know and twins are formed

facts about twinsfacts about twins

twins are more common in African twins are more common in African American families, and they are least American families, and they are least common in the families of Hispanics and common in the families of Hispanics and Asians. Asians.

Male–female twins are the most common Male–female twins are the most common result, about 50 percent and the most result, about 50 percent and the most common grouping of twins.common grouping of twins.

1)identical twins1)identical twinsthree main types of twins: three main types of twins: identical twinsidentical twins :occur when a single :occur when a single egg is is

fertilized to form identical which then divides into fertilized to form identical which then divides into two separate two separate embryos.embryos.

They have identical genes.They have identical genes.

““Its like looking like in a mirror”Its like looking like in a mirror”Identical twinsIdentical twins

identical twinsidentical twins, occur when a single egg is fertilized to , occur when a single egg is fertilized to form one zygote which then divides into two separate form one zygote which then divides into two separate embryos., embryos.,

The two embryos develop into fetuses sharing the same The two embryos develop into fetuses sharing the same womb. And two identical cells will result.womb. And two identical cells will result.

If the zygote splits after the first two days after If the zygote splits after the first two days after fertilization each cell may develop separately its own fertilization each cell may develop separately its own placenta and its own sac.placenta and its own sac.

Cases of Identical twinsCases of Identical twins

The identical twins can be of separate The identical twins can be of separate placentas and separate sacs. placentas and separate sacs.

Separate placentas separate sacsSeparate placentas separate sacs

Cases of Identical twinsCases of Identical twins

The twins share one placentas, and one The twins share one placentas, and one amnion sac (rarest combination). amnion sac (rarest combination).

fraternal twinsfraternal twins fraternal twinsfraternal twins:, usually occur when two fertilized eggs are implanted :, usually occur when two fertilized eggs are implanted

in the uterine wall at the same time. When two eggs are in the uterine wall at the same time. When two eggs are independently fertilized by two different sperm cells.independently fertilized by two different sperm cells.

The two eggs,, form two zygotes,.The two eggs,, form two zygotes,. They have same or opposite sex and they don't have to look at all They have same or opposite sex and they don't have to look at all

alike.alike. They have separate placentasThey have separate placentas

Facts about FRATERNAL twinsFacts about FRATERNAL twins

o Africa sees the highest incidence of Africa sees the highest incidence of fraternal twins; Asia, the lowest.fraternal twins; Asia, the lowest.

Female fraternal twins have a one in 17 Female fraternal twins have a one in 17 chance of giving birth to their own set of chance of giving birth to their own set of fraternal twins.fraternal twins.

Conjoined twinsConjoined twins

Conjoined twinsConjoined twins are joined at some region are joined at some region of their bodies. The many different types of of their bodies. The many different types of conjoined twins are classified by the area conjoined twins are classified by the area where the attachment is located:where the attachment is located:

How twins become conjoined?How twins become conjoined?

It results when an embryo start to divide It results when an embryo start to divide but fails to complete the process, and the but fails to complete the process, and the result is not quite two childrenresult is not quite two children

The twins originate from a single fertilized The twins originate from a single fertilized egg, so they are always identical and of egg, so they are always identical and of the same sex. the same sex.

It is believed that the first 13It is believed that the first 13thth and 15 and 15thth days after fertilization the malformation days after fertilization the malformation occursoccurs

Facts about Conjoined twinsFacts about Conjoined twins

Joined twins occur in about one in 100,000 Joined twins occur in about one in 100,000 pregnancies pregnancies

cases of cases of Conjoined twinsConjoined twins

PygopagusPygopagus - back-to-back, joined at the - back-to-back, joined at the rump (about 19 percent)rump (about 19 percent)


IschiopagusIschiopagus - joined sacrum to sacrum - joined sacrum to sacrum (about six percent) (about six percent)


CephalopagusCephalopagus - connected at the head - connected at the head (about two percent) (about two percent)


DipygusDipygus - one upper body with two lower - one upper body with two lower bodies (including the abdomen, pelvis and bodies (including the abdomen, pelvis and legs) legs)


ThoracopagusThoracopagus - joined at the chest; may - joined at the chest; may share a single heart or have some cardiac share a single heart or have some cardiac connection; some organs in the abdominal connection; some organs in the abdominal region may be malformed (about 40 region may be malformed (about 40 percent) percent)


OmphalopagusOmphalopagus - joined at the chest - joined at the chest (about 33 percent) (about 33 percent)


RachipagusRachipagus - back-to-back, joined along - back-to-back, joined along the spine above the sacrum the spine above the sacrum

Survival rate of conjoined twinsSurvival rate of conjoined twins

The overall survival rate of conjoined twins The overall survival rate of conjoined twins is somewhere between 5% and 25%. is somewhere between 5% and 25%.

If they have separate sets of organs, If they have separate sets of organs, chances for surgery and survival are chances for surgery and survival are greater than if they share the same greater than if they share the same organs. organs.

Conjoined twins are rare and have a poor Conjoined twins are rare and have a poor survival ratesurvival rate

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Twins - how can this be?