MHRA warns that buying more wireless CTG monitors than there are radio channels could cause signal crossover

What the MHRA found

The alert covers "classic telemetry systems operating within the Industrial, Scientific and Medical (ISM) frequency band where a limited number of channels are available." Drawing on incident reports and stakeholder feedback, the MHRA lists signal crossover between devices on the same channel, readings that differ from the actual fetal heart rate, recording that continues after transducers are removed, interference shaped by building layout, and user and maintenance factors such as improper docking, insufficient cleaning and incorrect configuration.

The most serious of these is crossover. In the MHRA's words: "In rare circumstances, signal crossover may result in the fetal heart rate from one CTG monitor being displayed on another CTG monitor operating on the same RF channel." The alert names no manufacturer or model and does not say how many incidents were reported.

Distance alone is not a dependable fix

Two devices on the same channel may need to be 100 metres apart to avoid crossover where there are no walls or pillars between them, according to the alert, and "the wall between adjacent rooms may not be sufficient." Crossover can also happen between floors, during patient transfers and when devices are moved between clinical areas. Device-specific separation advice is left to manufacturers' instructions for use.

The procurement warning

The alert's sharpest line is aimed at buyers rather than midwives: "Purchasing more devices than the number of available RF channels could lead to signal crossover, irrespective of whether the devices are from the same or different manufacturers."

Trusts are asked to assess the local RF environment, channel availability and the number of devices they need before purchasing. Installation should involve maternity services, clinical engineering (EBME), IT, the clinical safety officer and the manufacturer. EBME teams should keep a register of wireless CTG systems, channels, frequencies, bandwidth allocation, locations and paired devices, and every transducer and base station should be labelled with the channel it uses.

For clinicians, the alert asks for traces to be checked against maternal pulse and clinical assessment, for confirmation that the displayed heart rate belongs to the right patient, and for a wired CTG system to be available as a backup. Suspected incidents should be reported through the Yellow Card scheme, or to IRIC in Scotland. The alert was repeated in the MHRA's September safety roundup, published on 29 September.

Wireless CTG problems were reported in 2022, but not crossover

In April 2022 the Healthcare Safety Investigation Branch (HSIB, now HSSIB) published a national investigation into the equipment used for continuous fetal heart rate monitoring. It described wireless transducers as "problematic". Telemetry failed with distance, and staff reported that it also failed "if the mother went into the en-suite bathroom, regardless of how thin the walls of the bathroom were."

The report also found that trusts had read a line in NICE guideline CG190, "Offer telemetry to any woman who needs continuous cardiotocography during labour", as a requirement, and bought expensive equipment on that basis before discovering problems. HSIB recommended that NICE consider reviewing its telemetry recommendation (R/2021/138).

The 2022 report described signal loss, pairing problems, battery life and cost. It does not mention signal crossover, interference or radio channels. NICE's current guideline, NG229, published in December 2022, has two telemetry recommendations: keep wireless transducers charged and maintained, and switch to wired transducers if signal loss is not resolved by reducing the distance to the base unit.