It is understood the rate of conceptions plummeted to almost 0% over the past two months, alerting clinicians there was something seriously wrong.
Generally around 30% of women will become pregnant per cycle of IVF, with the GRI unit typically performing above that national average.
Infertile couples who had been undergoing IVF at the artificial conception unit in the Glasgow Royal Infirmary (GRI) are now being treated at the city's private Nuffield Hospital after NHS Greater Glasgow and Clyde (NHSGGC) observed a sudden decrease in the anticipated success rate at the unit over the period.
It is thought the fall may be linked to construction works near the department.
It raises the prospect that some couples may have suffered a setback in their plans to conceive a child.
The health board has so far been unable to identify what caused the decline in conceptions, but a full investigation has been launched and experts have ruled out a clinical explanation.
One possibility being looked into is that building works under way on the floor immediately above the unit, where clinical laboratories are currently being refurbished, may have disrupted or contaminated the artificial insemination process.
The GRI conception unit caters to women and couples NHSGGC, NHS Lanarkshire, NHS Ayrshire and Arran and NHS Dumfries and Galloway.
Around 25 NHS patients a week – including those who underwent treatment during the past two months – have been receiving IVF at the Nuffield's Assisted Conception Unit since November.
To ensure continuity for patients some medical, nursing and other clinical staff from the GRI unit are working with Nuffield staff to treat the NHS patients.
Until the mystery surrounding the alarming drop in conception rates is resolved, the Nuffield will carry out both the laboratory and surgery elements of IVF, although the GRI unit will continue to look after women coming in for check-ups or outpatient procedures.
Dr Helen Lyall, consultant gynaecologist at the GRI's Assisted Conception Service, said: "Assisted conception success is never guaranteed but we must make sure that every chance possible is given to every single one of our patients.
"The Glasgow Assisted Conception Service is recognised as an excellent unit, achieving higher than national average success rates. Patients using our service should be assured that our decision to temporarily move activity to the Nuffield Hospital was a decision based on putting patients first while we look into what might be the reason for the reduction in our normal success rates."
In Scotland, couples struggling to conceive are entitled to a maximum of three cycles of IVF on the NHS, including a minimum of two transfers of fresh embryos. It applies to couples where one or both partners have been diagnosed with infertility or where the couple has suffered unexplained infertility for at least three years. In around 25% to 30% of cases no cause can be identified.
David Snape, hospital director at Nuffield Glasgow, said: "The team at Nuffield are delighted to be able to help our colleagues in the NHS at this time and we are particularly pleased that, with the collaboration of both teams, the GRI has been able to deliver a seamless service to all patients currently in the system."
The IVF process is split into two major steps. In the first stage, the woman receives hormones to stimulate her ovaries into producing an increased supply of eggs – typically around a dozen – which are then harvested under anaesthetic by a gynaecologist using ultrasound and a long needle.
The eggs are then transferred from the theatre to laboratory-based embryologists, who mix the eggs with the partner's sperm in a petri dish to encourage fertilisation.
Around three days later a developing embryo or embryos are implanted into the woman's uterus in the hope of making her pregnant.
In the meantime, all these processes are being carried out at the Nuffield.