Arms up sleep sacks, also known as "swaddle sacks" or "wearable blankets with sleeves," can be safe if used correctly and are appropriate for your baby's age and development. These sleep sacks allow babies to have their arms up in a natural, self-soothing position, which can help comfort some babies and reduce the startle reflex.
Most experts recommend transitioning baby out of the swaddle sack by stopping arm swaddling around 2-3 months old. Look for signs your baby is trying to roll over, which means they need their arms free for safety. Use a transitional sleep sack with arm openings to slowly wean baby. Take one arm out at a time over a week or two if needed. By 3-4 months, switch fully to a sleep sack with both arms out.
Babies like sleeping with their arms up due to the natural Moro reflex, providing comfort and security. This reflex, causing arm extension in response to stimuli, is common in newborns and diminishes around 3 to 4 months. Arms-up sleep sacks cater to this preference, promoting better sleep by mimicking their natural position. Babies may also find self-soothing through finger or thumb sucking. The sleep position allows them to feel relaxed and secure, enhancing their sleep experience.