"Long periods sleeping in car seats may be dangerous for young babies," the Daily Mail reports.
The results of a small study suggest spending long periods of time in a car seat may lead to babies having breathing difficulties.
But the researchers pointed out "we cannot be certain of the clinical significance or potential risks".
This novel study used a vehicle simulator to look at the effects of placing a newborn baby in a car seat at the 40⁰ angle required for travelling.
Researchers tested 40 newborns, who were a mix of preterm and full-term.
They found that while sat at this angle for 30 minutes – either stationary or when in motion – the babies' heart and breathing rate increased, and their blood oxygen levels were lower compared with lying flat in a cot.
The difficulty is knowing whether this would put the infants at serious risk – for example, whether their risk of stopping breathing goes up.
We don't know how many harmful effects may occur while a baby is travelling in a car seat, so a larger study is now needed.
Until then, the safety of a baby travelling in a moving vehicle is paramount. It's important to continue to use car seats as instructed for any journeys – and is also required by law.
Francine Bate, chief executive of the Lullaby Trust, the charity who funded the study, advised parents to keep a watchful eye on babies travelling in a car seat, and to also avoid driving long distances without taking a break.
The study was carried out by researchers from Great Western Hospitals NHS Foundation Trust, Swindon, the University of Southampton and the University of Bristol.
The Mail gives fairly balanced coverage of this study, including making the recommendation that babies should travel in a properly secured child seat during car journeys, as required by law.
This experimental study involved using a simulator designed to reproduce the vibration a baby experiences when placed in a rear-facing car seat in a car travelling at 30mph.
Car seats are used for infants from birth up to 10kg, but may be too big to secure low birthweight or preterm infants who weigh less than 2.5kg.
There are concerns that the prominent back of the head seen in babies may push the head forwards when they sleep in these seats, and possibly obstruct the airway.
There are said to have been isolated reports of deaths while infants have been sleeping in these seats, either while travelling or when being used as an alternative to a cot or pushchair.
A BMJ study from 2006 found that in the 18 months between July 1999 and December 2000, a total of 43 babies who had been travelling in car seats required admission to hospital for serious breathing difficulties.
There have never been any studies that have actively monitored infants in moving vehicles before, so this moving simulation aimed to better establish how safe car seats are for babies while travelling.
The study aimed to assess the effects of placing healthy full-term and preterm infants in a car seat positioned at an angle of 30⁰ or 40⁰, either while static or moving.
The intention was to replicate the normal routine of parents preparing for and then taking their baby on a car journey.
Mothers of 40 infants – 19 full-term and 21 preterm – were recruited when the babies were ready for hospital discharge.
The babies were monitored continuously for their breathing rate, heart rate, blood oxygen levels and carbon dioxide levels on breathing in and out while spending 30 minutes in three different positions.
Half the infants were randomly allocated to be tested in the following order (protocol A):
The other half received this sequence in a different order (protocol B): static 40⁰, moving 40⁰, then static 30⁰.
The babies' breathing and heart measures when they were lying in a cot (baseline) were compared with those during the tests.
The static 30⁰ positions were tested using the babies' own car seats, as they were ready to go home. The 40⁰ tests used the same seat placed on a motion simulator in the lab.
In the full sample of 40 babies, the average pregnancy duration was 36 weeks (range 31 to 39 weeks) and the average birthweight was 2.5kg (range 1.5 to 3.2kg). Babies were tested an average of 13 days after birth.
Looking at the static 30⁰ positions, the only difference compared with baseline was more occasions where the blood oxygen levels were less than optimal.
There were, however, more changes when the babies were angled at 40⁰ and in motion. Babies in these positions had significantly higher heart and breathing rates, and lower blood oxygen levels. Their carbon dioxide levels rose slightly, but not significantly so.
There were also more episodes where blood oxygen levels were notably lower than normal – less than 85% saturation, when normal would be in the high 90s.
Comparing the preterm babies with the full-term infants, the changes were still in the same direction, but were less so than with the preterm infants.
The order of testing (protocol A or B) made no difference.
The researchers concluded that: "Term and preterm infants showed significant signs of potentially adverse [heart and breathing] effects in the upright position at 40⁰, particularly with simulated motion."
They went on to say a larger study is required to investigate the significance of these results.
This valuable pilot study is said to be the first to have assessed the effects of a newborn baby sitting in a car seat in the more upright position needed to safely secure them inside a moving vehicle.
The findings suggest spending 30 minutes sat in a car seat while stationary at the lower angle of 30⁰ has minimal effects.
But being placed in a car at the necessary 40⁰ angle, static and in motion, can have significant effects on the newborns' breathing and heart rate.
It's difficult to say whether the findings seen when a baby was positioned at the 40⁰ angle could be harmful and put them at potential risk of stopping breathing, for example. We also have no information on the effects of spending longer than 30 minutes in this position.
And although minimal effects were seen when the babies were placed at a 30⁰ angle, we don't know whether it could start to have an effect if the baby was left in the seat in this position for longer.
Because no studies have been done before in moving cars or simulators, the possible nature, frequency and magnitude of any adverse effects are unknown.
This makes it difficult to know the optimal sample size that would be needed to reliably capture any harmful effects – studies in a larger sample of babies are therefore needed to confirm these results.
The authors say the American Academy of Pediatrics currently recommends that all preterm infants should undergo monitoring in a car seat before discharge to check for low breathing or heart rate, or low oxygen saturation.
They say many UK neonatal units also follow a "car seat challenge" before discharging preterm babies from hospital. Even so, this doesn't take into account the effects of motion.
Further studies are needed to ensure the safety of newborns travelling in car seats. But for now, car safety remains paramount – parents and carers should continue to use car seats according to their instructions.
Dr Renu Arya, consultant paediatrician at Great Western Hospitals NHS Foundation Trust, who led the research project, said: "Parents should not stop using car safety seats to transport their infants. Infants must be protected in moving vehicles, and UK law requires car seats be used whenever infants travel in cars."
But it may be a good idea to rethink leaving a baby in a car seat for prolonged periods when they're not travelling.
Taking regular breaks when driving long distances is also recommended. As well as giving a baby a chance to move out of their car seat, it will also help keep the driver alert and reduce the risk of accidents.
The Royal Society for the Prevention of Accidents recommends taking at least a 15-minute break every two hours.