A Dutch IVF treatment centre has said that 26 women may have been fertilised by sperm from the wrong man. All couples have been informed of the potential mix up, the medical center said.
The BBC reports that the University Medical Center in Utrecht admitted to a "procedural error" during in-vitro fertilizations between April 2015 and November 2016, and that an investigation has been launched.
Half of the women who received treatment have so far become pregnant or given birth.
Some of the couples' embryos had also been frozen and stored to be implanted in the mothers' wombs at a later date, but there is a chance that they too have been created using the sperm from a man other than the intended father.
Although the chance of that happening was small, the possibility "could not be excluded", the centre added.
"The UMC's board regrets that the couples involved had to receive this news and will do everything within its powers to give clarity on the issue as soon as possible", the statement said.
The mistakes happened during a test tube baby technique which involves a sperm cell being directly injected into the egg. For a period of seven months, a lab technician used a tainted pipette to inject the sperm.
Of the 26 couples involved, nine have had children and four women are pregnant. Given that the UMC conducts about 700 ICSI procedures each year, there is justifiable cause for concern. "So people need to have 100% confidence in the method they adopt", it said. She reportedly sued her fertility clinic for negligence after she noticed that her son's skin and hair color were markedly different than that of her Caucasian husband.