| The increased concordance in dizygous twins over full siblings shows that the in utero environment is important. |
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| The zygote is dizygous, meaning two different eggs were fertilized by two different sperm. |
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| The incidence of multiple births increases with the age of the mother but distinctly more so for dizygous rather than for monozygous twins and more so still for triplets. |
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| However, in such cases the risks could not be quantified because the database did not differentiate between monozygous and dizygous twin pairs. |
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| Two studies comparing monozygous and dizygous twins may be cited. |
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