Crib Mattress Height: An Ages and Stages Guide

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When to Lower a Crib Mattress?

Crib mattress height depends on your baby’s age, size, and abilities. Newborns and infants who are younger than 5 months old and cannot sit up can generally sleep safely on a crib mattress placed at the highest position. Once a baby can sit up, or is able to roll over or push up onto their hands and knees, you should lower the crib mattress to the halfway position. As soon as your baby shows signs of pulling up to standing, you should lower the crib mattress to the bottom level.

Keep reading to learn the ages and milestones you need to look out for when considering your baby’s crib mattress height.

Crib Mattress Height: Why It’s Important

According to a 19-year study published in the journal Pediatrics, US emergency rooms treat an average of nearly 10,000 zero- to two-year-olds each year for crib, playpens or bassinet injuries. Of those, more than 80% involve cribs. Roughly 66% of injuries involving a fall from a crib, playpen or bassinet.

These statistics are as sobering as they are eye-opening. Clearly, safe crib practices are important to keeping babies safe. And that includes helping parents and caregivers understand when they should lower their baby’s crib mattress.

Crib Mattress Height Regulations

Crib falls injure babies with shocking frequency. Given how common it is, it’s no surprise the federal government regulates crib mattress height. These guidelines are set-up to create “escape resistant” sleep environments for babies shorter than 35 inches tall.

In the United States, the minimum distance between the top of the lowest support and the top of the crib side rails is 26 inches. Most full-size crib mattresses are between 5 and 6 inches thick. This means the actual distance between the top of the mattress and the top of the rails is 20 to 21 inches.

Our Ages & Stages Guide to Crib Mattress Height

Place Crib Mattresses in the Highest Position for Newborns

As long as your baby can’t sit up and is under 5 months, the highest position is likely safe.

When your baby is a newborn, it’s fine to keep it in the highest position. This will make it easier on your back when you’re lifting baby out of the crib, make it more likely you’ll be able to put your baby down without waking them, and also ensure you’re able to support your baby’s neck properly when lifting in and out of the crib. (source)

As a rule of thumb, you can keep your baby’s mattress in the highest position as long as they’re immobile. Once they can start moving on their own – this includes rolling and sitting unsupported – it’s time to lower it.

Lower the Crib Mattress to the Middle Height for Infants

Once a baby can sit up by themselves, it’s time to lower the crib mattress.

By the time your baby is able to sit up, roll over, or push onto their hands and knees, you’ll want to have adjusted her mattress to the middle height (one notch down from the highest position).

Most babies are able to sit by themselves between 5 and 8 months of age. Once they’ve mastered rolling and sitting, babies generally work on pushing themselves up onto their hands and knees.

At this stage, the highest position can be dangerous, as your baby may try pulling themselves to standing at any moment.

Place the Crib Mattress at the Lowest Position for Older Babies and Toddlers

When your baby shows any signs of pulling themselves to standing, lower everything to the lowest setting. This will make it harder for your baby to climb out of their crib. Lowering the mattress at the right time reduces the risk of falls and injury.

At this stage, it’s also important to remove any crib bumpers or wedges from the crib. These items are unnecessary and potentially unsafe at any time. They become particularly problematic once your baby can stand. Babies can use them as a makeshift staircase to climb out of their crib.

Time for a Toddler Bed

Once your child begins to climb or reaches 35” in height, transition them to a toddler bed. You can also transition them to a toddler mattress, which doesn’t need to be as firm as a baby crib mattress.

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