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. 」
精蟲在每毫升40x10^6以下的時候
受孕成功率會隨著精蟲密度增加而增加
但是超過四千萬以後成功率就不會再增加
所以根據研究12 億不會比四千萬更容易受孕成功