SALT LAKE CITY—The University of Utah has put together a panel of doctors and medical ethicists to review how a convicted felon working at a now-defunct university fertility clinic two decades ago switched his sperm and fathered a woman who is now 21.

University of Utah official Sean Mulvihill said Wednesday the school has received about 15 calls to a hotline it set up earlier this month. A couple of families are considering doing paternity tests.

The university has confirmed that felon Thomas Lippert replaced a customer's sperm with his own, fathering a girl 21 years ago.

So far, there are no other known cases of Lippert fathering children without the family's knowledge. But Mulvihill says there could be hundreds of families who haven't been checked.

He estimates 1,000 people came to the clinic during Lippert's employment, from about 1988 to 1993. Most of their records are now gone.