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Types of Twin Pregnancy


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  1. #1
    Parasakthi's Avatar
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    Types of Twin Pregnancy

    Fraternal Twins

    With fraternal twins (also known as 'non-identical twins'), the most common type, the mother contributes two eggs that each are fertilized in the womb by two different sperm cells from the father. The two eggs form two zygotes, and these twins are therefore also known as 'dizygotic' as well as 'biovular' twins.

    Fraternal twins, like any other siblings, may look very similar, particularly given that they are the same age. However, fraternal twins may also look very different from each other. They may be a different sex or the same sex. The same holds true for brothers and sisters from the same parents, meaning that fraternal twins are simply brothers and/or sisters who happen to have the same age. They are genetically as similar as any ordinary siblings.


    This type of twin is more common if there is a family history of twins, also more common for older mothers, with twinning rates doubling in mothers over the age of 35.

    They are also more likely to occur if fertility drugs are used
    to help you become pregnant.
    Identical Twins

    With identical twins, one egg (zygote) from the mother is fertilized by one sperm from the father, and then very early in development the embryo splits and two fetuses grow. Spontaneous division of the zygote into two embryos is not considered to be a hereditary trait, but rather a spontaneous or random event.

    If the zygote splits very early (in the first 2 days after fertilization) they may develop separate placentas (chorion) and separate sacs (amnion). These are called dichorionic, diamniotic (or 'di/di') twins. While all fraternal twins are 'di/di', this occurs 20 - 30% of the time in identical twins.

    Most of the time in identical twins the zygote will split after 2 days, resulting in a shared placenta, but two separate sacs. These are called monochorionic, diamniotic ('mono/di') twins.These twins are very similar genetically, and share a single afterbirth.


    Very occasionally, twins will also share the same sac (fluid cavity). In about 1% of identical twins the splitting occurs late enough to result in both a shared placenta and a shared sac. These are called monochorionic, monoamniotic ('mono/mono') twins.

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    Last edited by Parasakthi; 2nd Aug 2011 at 07:20 PM.

  2. #2
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    Re: Types of Twin Pregnancy

    Conjoined twins

    Finally, the zygote may split extremely late, resulting in conjoined twins. Popularly known as Siamese twins, conjoined twins occur in 1 in 100,000 births or 1 in 200 MZ twins. Conjoined twins can be identified via ultrasound in the early part of pregnancy. Apart from sharing placentas and membranes, conjoined twins also can also share body parts and organs. Occurrence of conjoined twins happens when the zygote divides late and doesn't split totally. The twins can be linked at any part of the body but both will be joined at the same place.


  3. #3
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    Re: Types of Twin Pregnancy

    Semi Identical Twins

    The 'semi-identical' twins are the result of two sperm cells fusing with a single egg, before becoming two embryos. An embryo created this way doesn't usually survive, but a few cases are known. 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).


  4. #4
    Sujatha Suji's Avatar
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    Re: Types of Twin Pregnancy

    For me this is toooo much of biology class

    I use to see in TV some competitions for Identical twins.. Twin babies looks cute in that.

    Thanks & Regards,
    Sujatha (Suji)
    ------------------------------------------------------
    Google Must be a Woman, it Knows Everything.

  5. #5
    Parasakthi's Avatar
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    Re: Types of Twin Pregnancy

    I like twins... especially girls


  6. #6
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    Re: Types of Twin Pregnancy

    Parasakthi really informative post, thanks for sharing..

    ப்ரிய தோழி

  7. #7
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    Re: Types of Twin Pregnancy

    thanks for ur replies..

    it encourages me to keep posting good articles


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