Pediatrics and Scare Tactics: From Rock-n-Play to Car Safety Seats

Is sleeping in a car seat dangerous?

Earlier this year, the Fisher-Price company relented to pressure from the AAP (American Academy of Pediatrics) and recalled 4.7 million of Rock 'n Play (RnP) baby rockers, which now presumably occupy landfills.  This recommendation stemmed from an "investigation" by consumer reports showing that since 2011, 32 babies died while sleeping in the RnP.  These deaths are tragic, but what does it mean?  In order to make sense of this "statistic" we need to determine a rate, based on the exposure period, something like "the rate of infant death in the RnP is 1 per 10 million RnP occupied hours" or something like that.  Then we would compare it to the rate of infant death sleeping in bed.  If it was higher, we would have a starting point for considering whether ceteris paribus, maybe it's the RnP that is causing the infant deaths.  We would want to know the ratio of observed deaths in the RnP to expected deaths sleeping in some other arrangement for the same amount of time.  Of course, even if we found the observed rate was higher than the expected rate, other possibilities exist, i.e., it's an association, a marker for some other factor, rather than a cause of the deaths.  A more sophisticated study would, through a variety of methods, try to control for those other factors, say, socioeconomic status, infant birth weight, and so on.  The striking thing to me and other evidence minded people was that this recall did not even use the observed versus expected rate, or any rate at all!  Just a numerator!  We could do some back of the envelope calculations with some assumptions about rate ratios, but I won't bother here.  Suffice it to say that we had an infant son at that time and we kept using the RnP until he outgrew it and then we gave it away.

Last week, the AAP was at it again, playing loose with the data but tight with recommendations based upon them.  This time, it's car seats.  In an article in the August, 2019 edition of the journal Pediatrics, Liaw et al present data showing that, in a cohort of 11,779 infant deaths, 3% occurred in "sitting devices", and in 63% of this 3%, the sitting device was a car safety seat (CSS).  In the deaths in CSSs, 51.6% occurred in the child's home rather than in a car.  What was the rate of infant death per hour in the CSS?  We don't know.  What is the expected rate of death for the same amount of time sleeping, you know, in the recommended arrangement?  We don't know!  We're at it again - we have a numerator without a denominator, so no rate and no rate to compare it to.  It could be that 3% of the infant deaths occurred in car seats because infants are sleeping in car seats 3% of the time!


I'm very interested in this study because if our son falls asleep in the CSS and doesn't awaken when we remove him from the car, we allow him to keep sleeping for an hour or so in the CSS.  Are we being reckless?  Why is it that the authors think that it is the CSS that is causing an excess risk of death above the expected rate when they don't even know the observed rate of death per hour in the car seat, nor do they know the expected rate for infants sleeping in the recommended arrangement?  Well, they explain, and here are some of their points we need to consider in turn:

1. CSSs should "not be used for routine sleep".
2. "Sitting and carrying devices (such as CSSs) were initially designed primarily for the transporting, feeding, and play of infants and young children."
3. In reference 4, 14 children died in car seats and 10 of them were not in a car at the time; and in reference 5, 30 children died in car seats.
4. "If a child falls asleep in a CSS while actively traveling in a motor vehicle, they should remain in the CSS until they are no longer traveling. If they are still asleep when they are no longer traveling, they should then be placed in a crib or bassinet."
5. "Despite AAP recommendations, infants often spend prolonged periods of time in CSSs when not traveling, and the CSS frequently is used as an alternative to a crib or bassinet." (Emphasis added.)
6. "When compared with other deaths, infants dying in sitting devices had higher odds of having a child care provider or baby-sitter as the primary supervisor at the time of death (compared with a parent or guardian)."

Let's go through some rebuttals:

1. Why not?  Because they (AAP) say so.  (Pediatrics. 2016;138(5):e20162940).  Classic petitio principii.  Appropriate for children, I suppose, who often ask why and are told by a frustrated adult "because I say so."
2. So, because something was designed for one thing, does it follow that it is not suitable for another?  Is this Aristotelian Telos in action here?  What is the evidence that the car sear was designed exclusively to be safe in a car?  What features of being out of the car make it less safe there?  Are there any logical responses to these questions?  If so, they are not given in the article.
3. These small series may have been the impetus for the current larger one, but they don't inform the relevant questions any better than it does.
4. Since sleeping in a CSS is dangerous outside of the vehicle, why don't the authors and the AAP advise to keep the child awake while in the CSS in the vehicle travelling?  What makes it safe for a baby to sleep in the CSS at any time, and if it is unsafe at all times, why not admonish against all sleeping in CSS?  They are silent on this, perhaps because it brings the absurdity of the underlying argument into sharp relief.
5. Ahh, there's the rub.  The authors probably didn't realize it, but with this sentence they gave a likely explanation for their findings - that the motion of the vehicle, during even a short trip causes a fussy child to fall asleep and then he is left to sleep for several more hours outside the vehicle.  Since most trips are short, this is very likely, and it reinforces the need for a rate per hour of sleep.
6. If it's the CSS that is responsible for the deaths, why does it matter who leaves the child in it, unless non-parent caregivers leave the child in the car seat for longer periods?  No answer is given to this obvious question either, but the likely answer is again that the exposure time to the seat is different when you analyze by caregiver classification.  Now, increased exposure time is consistent with the authors' argument, but it is also consistent with no increase in the rate of SIDS while sleeping in the car seat.

These authors and anybody making recommendations based on this study are engaged in what appears to be mythical, magical thinking.  The CSS is only safe when in a car.  Because it was designed that way.  So, it's safe for infants to sleep in it in the car - no need to awaken sleeping babies while driving!  But when you take that baby out of the car, some magical curse thing happens, and now you're placing the infant at risk of SIDS.  This whole thing borders on the preposterous.  Possible, but more likely preposterous.

Oh, come on Scott, you're being to hard on the AAP, they just want the best for those infants, and they don't have better data, and don't you want to err on the side of safety?

Yes, we should err on the side of safety.  But these data are fatally flawed because there is no rate and no rate ratio.  The AAP should get a lot of push back and up their game and try to do some kind of estimation of rate ratios.  It will require some better data collection but it will really strengthen their arguments and their recommendations.  A prospective study of how much time, say, 1000 families have their babies sleep in a variety of locations and positions may allow us to get some estimate of the exposure times.  Oh, but wait.  Since we made the recommendation before we got these data, it's too late now!  We have a self fulfilling prophecy!  Now all those SIDS deaths in car seats will be transferred to SIDS deaths in cribs, if I'm correct about what's going on here.

But here's the real reason why my child will be allowed to continue to sleep in his car seat:  because it's damned hard to get babies to sleep and awakening them after they are asleep is a real buzz killer for everybody.  Even if the authors are right, and the 3% of deaths in CSS in their cohort were 100% attributable to sleeping in the CSS, the benefit I can expect to get from not doing this any more is 3% of my demographic's annual risk of SIDS which is 5/100,000 per year - 3% of this is 0.0000015 annual risk of death.  I don't think it's worth it on an individual level even if I did believe their data show causation, and I clearly don't believe they do.  Recommendations based on data as porous as these border on irresponsible fear-mongering and scare tactics.  Because who would dare question or rebuff the AAP where the safety of their infant is at stake?

Oh, and don't worry about that baby in the pic - that car is moving, so he's perfectly safe!