AMSTERDAM — Twenty-six couples in the Netherlands are waiting to find out if the sperm that was used to fertilize their eggs at a reproductive technology clinic might have come from the wrong men.

The clinic, at the University Medical Center in Utrecht, said on Wednesday that a procedural error might have led to a mix-up in sperm.

“In each of these cases there is a small risk, small but it cannot be ruled out, that during the procedure, sperm cells of the mother’s own partner have been mixed with remaining sperm from a previous procedure,” Paul Geurts, a spokesman for the hospital, said in an interview.

In most cases, the egg will most likely have been fertilized by the intended sperm, but “we will have to see” to know for certain, he said.

The situation was discovered in November, according to Mr. Geurts, when a technician at the clinic noticed a problem in a kind of in vitro fertilization treatment known as intracytoplasmic sperm injection, or ICSI, and reported it.

That procedural error might have occurred for couples treated from April 2015 to November 2016, according to the clinic. Half of the couples who had fertility treatment during that time have already had children or are expecting them. The other half have fertilized eggs that are frozen. The oldest child who might have been conceived as a result of the possible mix-up is about a year old.

All of the couples possibly affected have been informed and have been offered DNA tests, the clinic said.

Primarily used in cases of male infertility, ICSI involves injecting a single sperm directly into a mother’s egg. The technician, guided by a microscope, injects the sperm using a glass pipette. The tip of the pipette is then discarded.

The technician, upon completing the procedure, discovered that there was still genetic material on the tip of the pipette, Mr. Geurts said. She notified the supervising technician, and upon further investigation, they discovered that sperm from a previous procedure had somehow gotten into the pipette — evidently because the technician had mistakenly used the wrong kind of rubber apparatus on the end of the pipette.

Mr. Geurts declined to say whether the technician had been punished, calling it a confidential personnel matter.

“The hospital regrets, of course, what has happened to the couples involved, and we will provide counseling and a meeting with the medical staff with all of these couples to work their way forward,” Mr. Geurts said. “It was just an unfortunate event.”

Jesper Smeenk, a gynecologist and spokesman for the Dutch Federation of Obstetricians and Gynecologists, said there were about 7,600 ICSI procedures every year in the Netherlands.

“Obviously, this is a very rare case, and we’d like to keep it that way,” Dr. Smeenk said in an interview.

The Netherlands has 12 clinics with laboratories that are permitted to perform I.V.F., he said. The clinic in Utrecht is one of the largest centers of its kind in the country.

“I’m a little bit worried that the general population will have the idea that I.V.F. is something that isn’t safe or hasn’t been safe or will not be safe anymore,” Dr. Smeenk said. “As long as the strict protocols are being followed by people in the laboratory or in the field, it is safe. In this case, a human error occurred because one person didn’t follow the protocols.”

Jose Knijnenburg, director of Freya, a Dutch patient organization for fertility issues, said she was “shocked that this has happened,” adding: “It’s a devastating experience for the patients concerned. The uncertainty is terrible, and they have to decide if they want to know if there was a mix-up or not. I would not want to have that choice.”

However, she added: “I’m not concerned about I.V.F. as a whole. It’s not the system, it’s not the clinic, but people are working, and people can make mistakes.” She said she knew of only one other such situation in the Netherlands.

That case, in 1993, involved a white mother who thought she had conceived twins from the sperm of a white donor, but gave birth to one white child and one black child.

Source: NYTimes