直接看研究
https://pubmed.ncbi.nlm.nih.gov/9777833/
“The probability of conception increased with increasing sperm concentration up to 40x10(6)/mL, but any higher sperm density was not associated with additional likelihood of pregnancy. ”
也就是每毫升40x10^6以上不会增加受孕成功率
4千万跟12亿两者对受孕成功率没有统计上的差异