Mater semper certa est
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Mater semper certa est ("The mother is always certain") is a Roman-law principle which has the power of praesumptio iuris et de iure, meaning that no counter-evidence can be made against this principle (literally: Presumed there is no counter evidence and by the law). Its meaning is that the mother of the child is always known.
Since 1978, when the first child was conceived by the technique of in-vitro fertilization, the principle of "Mater semper certa est" no longer applies, since a child may have both a genetic and a natural ("birth") mother.