The Altnagelvin Hospital Trust in Derry said over 70 women at risk of becoming pregnant had been contacted and the consultant gynaecologist responsible for unsuccessful operations to sterilise three women who later became pregnant had now retired from his hospital post.
In a statement last night the hospital authorities said the number of women involved in their investigations had risen from 43 to 74.
It is understood the investigations centred on women who, over the last four years, have been sterilised by the same consultant, now retired, using the same surgical procedure - the clipping of the fallopian tubes.
The statement, from the office of the hospital's chief executive, Mrs Stella Burnside, said: "Aware of the growing speculation and anxiety within the local community, the hospital issued a statement to the media to highlight a helpline service which it put in place for any women who had concerns relating to sterilisation issues."