^^^ Why is that?
Islamic laws are not Pakistani laws that it applies to ‘Aaam’ people and not to ‘Khaas’ people. When we talk about Islamic laws, then we are talking about laws of Allah that applies to all, regardless of who they are, and their status.
On the other hand, when Marium (AS) got pregnant, she was ordinary Jewish woman, and laws that were applicable on her were same as the laws applicable on other Jewish women. Even today, Jews do not believe on virgin birth and Christians believe on virgin miraculous birth came much after the birth of Isa (AS).
So, laws that Jewish society could have applied on Marium (AS) would have been same what Jewish society of the time would have applied on other Jewish women in similar situation.
As for Islam, we are told in Quran about it, and we believe that Marium (AS) is one of the four most pious women Allah has created … along with other three, who are Assia (AS), Khadija (AS) and Fatima (AS). Obviously, when we think of Marium (AS) and birth of Isa (AS), we look at it differently (due to our knowledge from Quran).
But for Jews of the time, pregnancy of Marium (AS) and birth of Isa (AS), all was sinister and against their religious beliefs. No angels came to announce amongst Jews at large that pregnancy of Marium (AS) and birth of Isa (AS) is miraculous and happened due to command of Allah.
If Jews of Marium (AS) time were as mentally retarded as Pakistani Mullahs of today, they would have seen pregnancy of Marium (AS) and birth of Isa (AS) in same way what Pakistani Mullah would see when they find any woman in same situation … and would have given same punishment to Marium (AS) what Pakistani Mullahs would try to give to innocent woman of today in similar situation.
But truth is that, Islam does not consider pregnancy as proof of sin, rather Islam demands 4 adult sane and truthful witnesses as proof of sin (adultery or fornication) … something many retarded Mullahs ignore as they use their non-existent brain to conclude. These retards could not comprehend that pregnancy can happen ‘with or without’ consent of woman and can also happen without even the knowledge of women as she might be unconscious, sleeping deep, or under the influence of drugs. In present days, pregnancy could even happen through artificial insemination.
I know that all these situations that can lead a woman to become pregnant is rarity, but validity of these situations are enough to put doubt in making pregnancy a valid evidence, especially when one is talking about civil crime (personal sins) like adultery or fornication. On the other hand, if rape has happened and girl has reported a case of rape, than obviously pregnancy can be taken into account for DNA purpose to determine rapist.
As for rape, that is different issue (something again Pakistani Mullahs could not comprehend). In rape situation, right of one individual (woman that got raped) is violated, and thus it becomes duty of state to provide justice to woman raped. State can do that by taking words (statement) of victim women seriously, giving her all sort of counselling, followed by prosecution of the culprit using whatever means of evidence state can acquire … medical reports, DNA tests, circumstantial and forensic evidences, various statements, and any other proofs available. After successfully prosecution the culprit rapist, state should give exemplary punishment to the rapist and huge compensation to the victim.