Getting help donating sperm. The younger brother could not be reached for an interview. Related Is a home sperm test useful? The number of children permitted from a single donor varies by law and practice. Human Reproduction Update. Some men who have joined the Donor Sibling Registrya site where donors and their children can connect, have been surprised and disturbed to discover that they have dozens of offspring. Read more about IVF. A guide for patients and their partners. Bex, United Kingdom. Keeping your sperm count high enough to make the grade means at least two — more often three — days of abstinence before each donation.