How did Islamic jurisprudence address cases of hidden pregnancy that could lead to the mixing of lineages, given the Sharia's emphasis on preventing the mixing of lineages?

Menstruation is a sign of the purity of the womb, based on the preponderance of probability, and the Sharia (definition) affirms this, even if a pregnant woman menstruates; this is because it is not common for a pregnant woman to menstruate. The occurrence of a presumption of the purity of the womb is sufficient, and if the contrary becomes clear, then one acts upon what has become clear. Modern devices have made it easier to confirm a woman's pregnancy.