Story highlights Dutch medical center investigating infertility treatment mix-up

Up to 26 women affected

Half of women in question have given birth or are pregnant

(CNN) A Dutch medical facility has launched an investigation after discovering that up to 26 women it was treating for infertility may have been fertilized with sperm from a man other than the intended father.

The investigation will cover fertility treatments that took place between mid-April 2015 and mid-November 2016 at the University Medical Center (UMC) in Utrecht . UMC described the mix-up as a "procedural error."

Half of the women in question have since given birth or are pregnant. UMC said that some frozen embryos may also have been fertilized with the wrong sperm.

All those affected by the error have been contacted. "We have been as transparent as possible," UMC spokesman Paul Geurts told CNN.

Women receiving ICSI treatment

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