The main thing to do IVF is to ensure that there is enough sperm, so different time requirements are used for different cases. If the previous sperm test is normal and the sperm between 48 hours and the seventh day after spermatozoa discharge are in the normal range in terms of number, motility and morphology, it is sufficient to follow this requirement. For patients with oligospermia, if the time is too short, the sperm count will be even lower, so sperm from 5-7 days after spermatozoa discharge is better. For patients with weak spermatozoa, the sperm will be in a better condition in the short time range, so IVF will be better in the range of 2-4 days after sperm discharge.