Papers presented at the monthly board meeting of NHS Greater Glasgow and Clyde said the circumstances surrounding a fall in pregnancies at Glasgow Royal Infirmary's Assisted Conception Service were still under review, but no one single issue had been identified as the cause.
The Herald revealed earlier this month that conception rates at the unit had plummeted from around 30% to 15% between September and November.
Building work on the floor above has been suggested as a possible cause of contamination.
The health board has transferred its IVF patients to the private Nuffield hospital in Glasgow for treatment and offered couples who may have been affected by the problem a complimentary cycle of IVF.
An update presented at a board meeting yesterday said: "The service moved off-site in the second week of November 2012 and the review was under way.
"To date no one single issue had been identified as the cause of the downturn in the percentage of fertilisation which would normally be expected, although it was noted that building work was ongoing within this area and that aspect, along with a full review of the clinical aspects of the service, was being considered.
"The practicalities of offering a further cycle to those patients who may have been affected during the period under review would be worked through as soon as possible."
The health board has to submit the findings of its investigation to the Human Fertilisation and Embryology Authority, which regulates IVF in the UK.