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HOW TWINS ARE FORMED?
 Identical twins are conceived through the ovulation and fertilization of one egg. However, where a single child conception pregnancy divides the zygote into what will become the placenta, embryo, and amniotic sac; the identical conception will further divide the zygote into two separate and nearly identical zygotes.
Identical twins can share a placenta or each develop their own. This is done before the zygote moves down the fallopian tube and embeds itself in the endometrium.. If the two zygotes move down the fallopian tube separately then each will separately attach itself for growth. This creates double embryos which will develop their own placentas. In turn, the zygote split can be put off until it has already embedded itself in the endometrium. This condition yields the opposite effect of the previously discussed situation creating double embryos that share a single placenta.

Although both are twins, non-identical or fraternal twins are conceived in a surprisingly different way from both identical and single child conception. Instead of a zygote splitting to create the set of twins, these twins are brought about by the production and fertilization of two separate eggs by two separate sperm. . As both eggs are separate they are allowed to travel separately down to the uterus.


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