Birth control can prevent that. Such as condoms or diaphragms.
The data you will collect is the blood phenotype.By adding serums that each contains a particular antibody such as anti-A, anti-B, or anti-D ... to see if there's an agglutination with erythrocytes' antigen and the antibodies, proving the presence of the appropriate antigen in the blood.
This will help to confirm the blood grouping if this technique is done in parallel with the plasma test ( of Simonin-Michon).
