A national sperm donation register would stop "prolific" sperm donors from creating more families than legally allowed, a peak fertility body says.

The Fertility Society of Australia and New Zealand is concerned online services are helping sperm donors create families in multiple states and territories without official documentation.

The lack of regulation and records presents considerable medical and legal risks for all parties involved, the society's president Luk Rombauts says.

"In accredited fertility clinics, all sperm donations are recorded, and professional screening and quarantining procedures are in place as accepted practice to provide appropriate health safeguards," he said.

"With online sperm donations, there are no appropriate screening protocols for sexually transmitted or genetically linked diseases (and) no professional counselling to help people make informed decisions about this procedure."

Prof Rombauts said without a national register, prolific online donors are able to breach legal limits on the numbers of families they create.

Those limits range between five and 10 families depending on the jurisdiction.

Breaching those caps can also increase the risk of accidental incest, Prof Rombauts said.

"Nobody seems to be asking how donor-conceived children will feel growing up knowing that they are part of large group of half-siblings, and it also raises the real prospect of accidental consanguinity," he said.

The fertility body has backed the Australian and New Zealand Infertility Counsellors Association's calls for a national sperm donation register.

The association is writing to the federal health minister, pushing for a national system and a parliamentary inquiry into the lack of regulation of online sperm donations.

"A proper national register would monitor the number of families created from the same donor, guide and inform potential recipients of sperm donations, and support donor conceived offspring with knowledge of their biological heritage," Prof Rombauts said.