The only way a man can be a "natural" sperm donor is by engaging into sexual intercourse with the woman wishing to conceive. Although this practice is rather common among single women willing to have a baby, the truth is, it is totally unadvisable.
Take into account that it has two major drawbacks which should be addressed carefully:
- The donor is not screened or tested for diseases and viral infections likely to be inherited by offspring, with the subsequent risk it involves for the pregnant woman and the fetus.
- There is no legal contract stating that he relinquishes his rights over the child born as a result of his donation.