An inquiry has been launched after the rate of pregnancies at the Assisted Conception Service at Glasgow Royal Infirmary, the largest fertility clinic in Scotland, plunged from 30% to almost 15% between September 1 and November 9.
Patients have been transferred to the private Nuffield hospital until the cause of the crisis is established.
Building work on a floor above the laboratories where the embryos are created may have led to contamination, but two months after the probe began no explanation has been found.
One 30-year-old patient who underwent ICSI – a form of assisted conception where an egg is directly injected with sperm – in August, immediately before success rates began to drop, said she feared she may have been affected.
She said: "I have outright asked them what the contamination was, when it happened, where it came from and what effect it had and they won't tell me."
"It is so emotionally draining that you expect to have the best conditions possible."
Writing on the Fertility Friends forum, one woman in her 40s who paid for IVF treatment in August said she heard a nurse telling her surgeon they were "having some problems with the incubators".
A spokeswoman for NHS Greater Glasgow and Clyde health board said: "We have already been in direct contact with the IVF patients who were being treated within this period.
"We wish to reassure IVF patients treated prior to September 1, 2012, and patients undergoing ICSI treatment within this timeframe there is absolutely no cause for concern."