Embarrassed officials at Altnagelvin Hospital in Londonderry have also admitted that 44 other woman who were sterilised by laparoscopy have been told that they, too, are "potentially at risk of pregnancy".
The laparoscopy operation has been used in United Kingdom hospitals for 15 years and has an expected failure rate of one in every 500 cases.
One of the three women said: "I'm very angry. I had doubts about undergoing the operation in the first place.
"It was a very difficult decision for me to make, but once I had taken the decision to be sterilised, the last thing I expected, let alone needed, was to become pregnant.
"How can I ever trust this hospital again after this blunder?
Stella Burnside, the hospital's chief executive, admitted that there had been a higher-than-expected incidence of failure of sterilisation.
"A review of this unusual incidence is currently underway," her statement said. "The procedure for this treatment is well tried and this occurrence is extremely unusual.
"Nevertheless, we have launched an urgent inquiry and ensured that each affected person is being offered specific advice, investigation and, where necessary, further treatment.
"We know that this is confined to a limited number of patients who underwent this procedure," the chief executive added.Reuse content