(CNN) A fertility doctor suspected to have fathered scores of people by secretly swapping donors' sperm for his own will have his DNA tested, after a Dutch court supported a legal challenge by 22 of his potential children.

The group were all conceived with the help of fertility doctor Jan Karbaat, who died in 2017 at the age of 89 and had long been suspected of using his own sperm to impregnate clients -- a charge he denied.

But a court ruled Wednesday that Karbaat's family must allow his DNA to be examined, after agreeing that there was sufficient evidence that he did use his own sperm.

DNA from Karbaat's son, who is still alive, has already been found to hold a "relevant biological relationship" with 47 people the doctor helped conceive, and a documentary that aired in the Netherlands suggested Karbaat may have fathered up to 200 children.

The court also agreed that it is "undisputed that a number of donor children have similarities in appearance" to Karbaat.

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