During the first 3 months of her life, your baby is going to sleep a lot. In fact, for these first 3 months of life, babies sleep between 14 and 17 hours of sleep in every 24-hour day. On the other hand, this sleep is mostly going to happen in short burst, generally not longer than 1 to 3 hours long, though some babies learn to sleep for several hours in a row at night.
These short bursts happen for two reasons. First, babies and newborns’ sleep cycles are shorter than adults - an adult sleep cycle generally lasts about 90 minutes, while a baby’s sleep cycle is only about 60 minutes long. The second and more practical reason, though, is that babies’ stomachs are so so small they only fit a few ounces of breast milk or formula, and they do so much growing in these early months, that they need to wake up and refuel by feeding every few hours, so they’re all energized and ready for their next naps.
As your baby gets a little older, some time in the first few weeks, her sleep patterns will start to get a little more predictable, and will probably start to fall into some kind of schedule all on their own. For babies to be able to sleep several hours in a row they need to learn to connect their sleep cycles and instead of waking up when each cycles ends, which can take some time. They also need to learn to feed efficiently, so they can refuel quickly when they wake up.
Since, in these first few months, your baby is probably going to be waking up so often to feed that new parents can start to have a little trouble telling day from night themselves. It can be hard to tell how your baby is going to learn to start distinguishing between little naps and the big sleep-time that night is eventually supposed to be. As she grows, though, she is going to start to be able to sleep for longer and longer periods of time.
You can encourage her to have longer stretches of sleep at night by making sure she sees some natural sunlight during the day, and by keeping her in relative darkness in the evening and at night, by using dim lighting, or even red bulbs, and by keeping her room dark at night. Darkness stimulates the body's production of melatonin, the hormone that promotes sleepiness, and letting your baby have a little darkness in her life can help her body learn when longer sleeps should start to happen.
Another way to help your baby learn about circadian rhythms (the sleep patterns that go along with day and night) is to pay attention to her napping routine as it develops. Even parents who feed and put their babies down for naps completely based on their babies’ cues and demands start to notice that their babies are sleeping at more predictable times, as those first few weeks wear on. Parents who notice what these patterns look like can sometimes influence them by slowly moving certain naps forwards or backwards to make the sleep schedule fit more neatly around a more conventional day-night sleep schedule.
The American Academy of Pediatrics and the National Sleep Foundation recommend that babies this age get between 14 and 17 hours of sleep in a 24-hour period, and they recommend this because, for the vast majority of children in this age range, it's the amount of sleep they need for healthy growth and development.
A little extra sleep generally isn’t a problem in itself unless it gets in the way of feeding, or if a baby isn’t growing at a healthy rate, or is lethargic instead of alert when she is awake. When accompanied by other symptoms, sudden added sleep can be a sign of illness. Too little sleep can lead to irritability and poor growth and development.
Newborns are only just learning to link their sleep cycles together, and sleep disruptions can get in the way of that lesson. Unfortunately, babies are also noisy sleepers who are likely to make sounds, move around, or even cry out in their sleep, and parents who respond too fast to these noises can easily wake them by accident. If you hear a sound, it can be helpful to pause and observe your baby, and carefully decide whether she is actually awake, or just transitioning between sleep cycles.
In addition, new parents can help themselves out later on by simplifying their babies' sleep requirements early on. If you can avoid getting into the habit of rocking, bouncing, or feeding your little one to sleep every night, she has a better chance of not depending on those things before she can fall asleep. Instead, try to put her down when she is sleepy but awake.
In the end, like all parts of your baby's growth, what’s most important is that she finds a sleep pattern that keeps her happy and growing healthily, and guidelines for what amount of sleep that involves are just that - guidelines.