The administration of the sperm donor bank of the Leids Universitair Medisch Centrum (LUMC) was a shambles, with donor data going missing and some donors fathering over 25 children in the same area, increasing the risk of incest, the hospital has said following an internal investigation.

The investigation was started following requests for information from children who had been conceived via artificial insemination between 1977 and 2004, when the sperm bank was operational, the hospital said.

A subsequent analysis of the data showed that there is no known donor on the books for 80 of the 1,141 registered children. In addition, the sperm of nine donors was also used more often than the allowed maximum of 25 times. In total, nine donors fathered over 400 children, with one single donor fathering as many as 90.

The rule that a single donor could father no more than a total of 25 children divided over 12 women was introduced in 1992 to prevent possible cases of incest and inbreeding which can lead to birth defects.

“That is a very real possibility,” LUMC board member Martin Schalij told broadcaster NOS. The women who used the sperm bank were nearly all from the west of the country, in the postal code areas 2000 to 3000. That means they are geographically close, increasing the chance that half brothers and sisters may meet and start a relationship, she said.

The hospital is now calling on mothers and children to contact the hospital.

Schalij said other clinics should also review their data. “It may well be that all the other sperm banks kept a detailed register but I wouldn’t be surprised if more questions will be asked. I think it would be a good idea to clear up everything once and for all.”

Donor child foundation Stichting Donorkind spokesman Ties van der Meer said such a move is long overdue. “We know that this is the tip of the iceberg. Files and archives at many other hospitals and clinics are also incomplete or a mess,” he said.

The FIOM expertise centre, which deals with questions surrounding kinship, said the findings of the LUMC will “cause unrest among donor children and their parents”.

“Very often children don’t know they have been conceived via artificial insemination, and it’s a big family secret, “ donor conception expert Janneke Maas said. “It is important parents are open with their children, including when they are in their thirties or forties.”

The case is the latest in a series of scandals concerning administrative chaos and unauthorised use of sperm. Just last week a former lab worker at a Leiden fertility clinic was found to have fathered 11 children illegally. He was also found to have a hereditary disease.

Fertility doctor Jan Karbaat, in the first case of unethical conduct by gynecologists to come to light in 2019, is thought to have fathered some 80 children.