Going through IVF with wife. All tests of sperm has been in the 10-16 million range. Donated for implantation and it dropped to 50 total. Reasons?

Abstinence. Many factors affect sperm numbers. The length of the abstinence period before collection is a common factor. A recent high fever or illness could be a factor. If the sperm function is normal then no worries, as your wife probably had fewer eggs than sperm. Icsi can be used for unexpected changes. The babies will be normal too. Best wishes.