About seven years ago Cynthia Daily and her partner used s perm donor to conceive their child, and held on to hopes that their son would one day meet some of his half siblings.

In a move that can be considered creating an extended family in modern times, Daily searched a Web-based registry for other children fathered by the same sperm donor. She created an online group to track them down and watched the number of children in her son's group increase. And then it grew some more - to 150 children fathered by the same sperm donor.

It's wild when we see them all together - they all look alike, Daily, a 48-year-old social worker in the Washington area, said. She reportedly sometimes vacations with other families in her son's group.

Daily's story was first told by The New York Times, and it has reignited debate this week as to whether there should be government regulations on sperm donorship.

Cases like the Daily's have raised concerns and fears that children from the same donor could share disease-causing genes that can spread through the general population, or possibly lead to accidental incest between half siblings who often live close to one another.

My daughter knows her donor's number for this very reason, one mother of a teenager conceived via sperm donation in California told the media. She asked to remain anonymous to protect her daughter's privacy.

For sperm donors, simply passing on their genetic code is just another way of making some extra money.

Now, critics are saying that fertility clinics and sperm banks are earning huge profits when they allow too many children to be conceived with sperm from popular donors.

We have more rules that go into place when you buy a used car than when you buy sperm, said Debora L Spar, president of The Baby Business: How Money, Science and Politics Drive the Commerce of Conception, to The Times. It's very clear that the dealer can't sell you a lemon, and there's information about the history of the car. There are no such rules in the fertility industry right now.

Critics are calling for legal limits on the number of children conceived using the same donor's sperm. They are also asking for a re-examination of the anonymity that hides many donors.

While there are no limits on the number of children a sperm donor can father in the U.S., in countries like Britain, France, and Sweden, the sperm donors are limited in the number of children they can father, according to reports.

It is estimated that between 30,000 and 60,000 children per year are conceived by sperm donors in the U.S.