How can women deliver twins? how does the fertilisation differ from single child to twins/triplets?
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Fertilization of identical twins (or triplets or higher) happens when one sperm enters one egg and the egg divides. (The process is called cleavage) Every egg divides evenly from one cell to two to four to 8 to 64 and so on, but in twins the entire collection of cells splits itself again – so say this happens right at the beginning (for easier math!) and the 64 cell morula would split into two identical 64 celled morulas before then doubling and going on to form a blastocyst and all the other stages of zygote. Instead of one there are now two (or three or 4 etc) complete groups that coukd go one to form “twins.” These would have identical DNA. But depending on when and where the split occurs in the development they may or may not look completely identical. If the split should fail to be complete the two groups of cells would go on to form a pair of conjoined twins.
Now for fraternal twins two sperm make it to two separate eggs. They could both be from the same ovary or one egg from the left and one from the right. These cells are not alike and do not share identical DNA, other than being born at the same time, they are no more alike than any siblings.
For birth of twins the babies birth one at a time – often with one head down and the second breach, but not always. Many doctors insist on Cearaean sections. But with good care it’s not necessary.
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