Answer
It helps prevent an RhD-negative person forming lasting antibodies after exposure to an RhD-positive baby's red blood cells. Those antibodies could otherwise affect a later RhD-positive pregnancy.
Sources for this answer
- NHSNHS · NHS medicine guidance
- Rhophylac 300 (1500 IU) — Current selected SmPCemc · Summary of Product Characteristics
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.