If boy do masturbation in his hand and have a sperm on his fingure and then clean it from hanky and put a half fingure in vagina so she get pegnant?

Not likekely. Sperm must travel in a liquid spermaric fluid and highly doubtfil that unless the handkercief was soaked with semen and then transferred to finger and then to vagina-low chance of pregnancy-but it not impossible.

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If boy do masturbation in his hand and have a sperm on his fingure and then clean it from hanky and put a fingure in vagina so she get pegnant?

Pregnancy. It takes live sperm to be introduced into the vagina for pregnancy to occur. The most reasonable thing is to wash your hands after mastrubation to minimize any chance of introducing live sperm. Your risk is low but not zero. Pregnancy is not the only concern as you should also be screened for any sexually transmitted infections, so that you are not passing on any unknown infections too. Read more...