Zwolle, Netherlands - A now-deceased Dutch gynecologist fathered at least 17 children after he inseminated women with his semen without their knowledge.

The man worked in the fertility clinic of the former Sophia hospital, now known as Isala hospital, in Zwolle between 1981 and 1993.

The gynecologist, who died in 2009, used his own sperm instead of the sperm of anonymous donors without the impregnated women's knowledge. 

The case came to light after some of the children independently went in search of their biological father. All their DNA samples ended up matching with each other, as well as with a relative of the doctor.

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The Isala Hospital made the news public on Tuesday and admitted the need for more transparency when it comes to sperm donation. In a statement, Isala condemned the doctor's actions as "morally unacceptable."

The doctor fathered at least 17 confirmed children, but there might be more, the hospital said. To check if other children were born from one of the doctor's fertility treatments, Isala has since created a DNA profile for the gynecologist. 

This is not the first case a fertility specialist in the Netherlands used his own sperm to impregnate his patients. A controversial doctor fathered at least 49 children in the 1980s and 1990s at a since-shuttered fertility clinic in Barendrecht. The women involved were completely unaware.