Foetal heart rate is just one of many tests doctors use
Doctors are warning expectant parents that at-home foetal heart rate monitors should be used only for "fun" and not as an alternative to medical advice.
The devices, which pick up the sound of the baby's heartbeat, can give "false reassurance", the British Medical Journal reports.
They can also cause unnecessary anxiety in untrained hands, doctors warn.
The Royal College of Midwives said the availability of the devices was of concern to their members.
The warning comes after a 34-year-old pregnant woman used her foetal monitor after she noticed her baby moving less frequently when 38 weeks pregnant.
Over the weekend she had reassured herself by listening to the baby's heartbeat but went to hospital on the Monday after being unable to detect it.
An urgent ultrasound showed the baby had died in the womb and doctors believe the patient had been picking up her own heartbeat or placental blood flow with the device.
Although the tragic death may have been unavoidable, the use of a foetal heart monitor certainly delayed the patient attending hospital, says Dr Abhijoy Chakladar, an anaesthetist at Princess Royal Hospital in Sussex, who treated the patient and highlights the issue in the BMJ article.
He is quick to point out that stillbirth is a rare event and pregnant women should not be unduly alarmed.
"These monitors are great fun as long as they are just used for a bit of bonding with the baby or play with older siblings.
"But they become dangerous when they're used by untrained people as an alternative to seeking medical attention.
"Expectant mothers who notice a reduction in foetal movement or have any other concerns about their baby's health should instead contact their midwife or labour ward for expert advice and reassurance."
It is the second such case highlighted this year in the BMJ.
Doctors previously raised the problem of false reassurance with a baby who survived but required neonatal intensive care.
A spokesman for the Medicines and Healthcare Products Regulatory Agency said it was aware of the case.
But he warned: "Members of the public using foetal monitors at home are unlikely to have the necessary knowledge or experience to use the device effectively and if they are concerned about the health of their baby they should seek medical advice."
Donald Peebles, spokesman for the Royal College of Obstetricians and Gynaecologists, said the devices did not really give much information anyway.
"If you're just doing it for fun and you can't pick up the heart rate because you're pointing it in the wrong direction that would unnecessarily frighten you.
"And it shouldn't be used to provide reassurance."
Mervi Jokinen, from the Royal College of Midwives, said: "These devices may be sold as a bit of fun for parents to use, but let me be categorically clear; there is absolutely no substitute for speaking to your midwife or doctor as soon as possible if you think that there is something wrong during your pregnancy."