Seven years ago, Cynthia Daily and her partner used a sperm donor to conceive a baby, and they hoped that one day their son would get to know some of his half siblings - an extended family for modern times.

Daily searched a web-based registry for other children fathered by the same donor and helped create an online group to track them. Over the years, she watched the number of children in her son's group grow.

Today there are 150 children, all conceived with sperm from the same donor, in this group of half siblings, and more are on the way, reports the New York Times.

With the number of children born through artificial insemination is increasing, many young people are discovering they have several or even dozens of half siblings in the world.

As more women choose to have children on their own, the demand for sperm donors has increased. However, Americans are now concerned about the implications of having many children fathered by the same man.

The primary concern that is cropping from this trend is that genes for rare diseases will now spread more quickly through the population. Experts are also concerned that accidental incest might occur between children fathered by the same donor.

Doctors and parents are pushing for the fertility industry to have greater regulations.

Some experts are even calling attention to the increased odds of accidental incest between half sisters and half brothers living close to one another.

Critics say that fertility clinics and sperm banks are earning huge profits by allowing too many children to be conceived with sperm from popular donors.

The sperm donor process is going well for fertility clinics. At the same time, the idea of nearly 150 children with the same genetic father amassed inside similar social circles and relatively close proximity can raise alarms.

There are advocates who believe that legal limits must be placed on the number of children a clinic can produce from the same donor's sperm.

Advocates for sperm donor laws and regulations say donors are protected by an anonymity that appears eerily familiar to the internet's earliest days when public users signed on with fictitious monikers.

150 children fathered by a single source can be overwhelming. It is difficult to believe that a sperm donor, despite the clinical process that he volunteers his sperm, feels no moral and ethical responsibility or concern for the children he has fathered.