Sleeping patterns vary with each child and gradually evolve over the first year. Sleep habits are influenced by the baby's temperament and feeling of being well fed and the parents' response to waking episodes. Some babies naturally seem to need more sleep than others.

A newborn moves between sleeping and waking during a 24-hour day. In the next 3 months, maturing of the brain allows the baby gradually to sleep for longer periods. By the third or fourth month, most babies sleep for their longest period (up to 7 to 8 hours) during the night and develop set nap times.

Babies have sleep cycles with periods every 50 to 60 minutes of active sleep, characterized by murmuring and restlessness. This restlessness usually lasts a few minutes, and if babies are left alone, they usually fall back to sleep.

The sleep cycles include:

• Drowsy sleep. The baby moves little but may be wakened easily. His or her eyes may start to close or gently open. Drowsy sleep can occur at the start or end of the sleep cycle.
• Quiet, or deep, sleep. The baby moves very little; has deep, regular breathing; and has no noticeable eye movement under the eyelids. The baby is not wakened easily.
• Active, or light, sleep. The baby appears restless and breathes quickly and irregularly. Eye movement is noticeable under the eyelids. A 1-month-old may spend about 50% of her or his sleep time in active sleep, while older children and adults spend about 20%. It is believed that a baby has longer periods of active sleep than an adult because the brain is developing rapidly.

At first, babies often sleep through loud noises. But, at about 3 to 4 months of age, many babies become easily disturbed by noises like the phone ringing or a dog barking.