The number of pregnant women who claim to have suffered sexual discrimination while working at Bloomberg, the financial news and data group, has grown from three to 58, it emerged in a pretrial hearing yesterday.

Raechel Adams, a lawyer for the US Equal Employment Opportunity Commission (EEOC), told a federal judge that since her agency filed its lawsuit in September, the number of women claiming that their duties were curbed, or promotion prospects were reduced after their pregnancies emerged, had grown significantly. The trial is expected to begin in the autumn.

Furthermore, Ms Adams, who is preparing a class-action lawsuit against the company, told US District Judge Loretta Preska during a hearing in New York that she expected the number to continue to grow. She has sent questionnaires to 478 women who were at Bloomberg since 2002 and has not finished interviewing them.

The EEOC took action after Jilly Patricot, Tanys Lancaster and Janet Loures filed charges with the government agency, each seeking at least $48 million (£24 million) in damages. Ms Patricot and Ms Loures are still with the firm. They alleged that a culture of sex discrimination was fostered by top managers, such as Michael Bloomberg, the founder who stepped down as chief executive in 2001 to run successfully for Mayor of New York. Mr Bloomberg still owns a 68 per cent stake in the company.

A complaint accused one of Bloomberg’s senior executives, Alexius “Lex” Fenwick, of telling another executive to fire two pregnant employees, saying: “I’m not having any pregnant bitches working for me.”

Bloomberg declined yesterday to comment on the case. But the group has denied the allegations in the past, with a spokeswoman saying: “We intend to defend ourselves vigorously against these outlandish claims. It sounds like an effort to damage reputations and to stir up publicity to pressure the company for financial gain. The company is proud of our track record in treating our people well.”

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