Artificial insemination requires a TMSC (total motile sperm count) of at least 3 million, i.e. at least this concentration of sperm must be moving adequately to have a chance of reaching the egg and fertilizing it.
On the other hand, for in vitro fertilization or ICSI, no minimum number of sperm is required, especially for ICSI, since only one sperm is chosen for each egg and introduced directly into it.
For more information about TMSC, see this link: Advanced Semen Analysis: Evaluating the Motile Sperm Count.
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