Normal gestation (pregnancy) is 40 weeks long, which is actually 10 4-week lunar months, not 9 as is the common thought. Sorry ladies, you are actually supposed to be pregnant a little longer than 9 months for a full-term healthy newborn. A premature baby is any baby that is born before 37 weeks of gestation. Why 37? At that point all the baby's systems are basically fully developed and they are able to breathe, eat, and function basically on their own without any problems.
For the NICU, our cut-off point for general prematurity is 35 weeks. Anyone born younger than than 35 weeks will automatically be admitted to the NICU for our extra care and support during their last weeks of development. At 35 weeks, we often come to the delivery to evaluate the infant and if there is any question in their ability to transition to extra-uterine life, they come to the NICU. Of course, we do get 'older' babies born at 'term' for different reasons that we'll discuss later.
A 25-week baby on a ventilator
The edge of viability for current medical advances is about 23 weeks of gestation. Mind you this is just a little under 6 months of pregnancy. At this point most mothers are just really starting to look "pregnant" and developing their tell-tale pregnant belly. These babies will have a lot of problems to overcome and will likely be given a lot of outside support by NICU staff. Also, it is very likely that they will spend at a minimum 3-4 months in the NICU before being able to go home. Most of the infants born this early actually spend even longer in the NICU - so expect a stay more like 4-5 months with lots of hurdles to overcome also. (we'll talk more about why later on as well). These babies are often less than 2 lbs and may be no 'taller' than a pen. Their limbs are tiny and thin and you can see every bone in their little bodies. Their skin is very thin, moist, and easily torn - we must take great care to keep their skin moist, healthy, and take very delicate care of them. Before 25 weeks gestation, their eyes are usually still fused together, and the skin of their eyelids is very thin - therefore they are very sensitive to light and we must keep their beds dark and cover their eyes from any outside light to protect their developing eyes. They cannot eat by bottle and need a tube placed to their stomach through which we place mother's breastmilk or formula. Every system is still developing and they need a lot of support.
The mid-range preemies are about 28 weeks until about 31 weeks. At this point in development they still have a ways to go, but they likely make it through their NICU stay and leave us just around when their birthday was supposed to be and may leave with some long-term medical needs. These babies are usually born aournd 1-3 lbs or more. Their skin is still thin and they need help to stay warm and not loose too much moisture through evaporating. Their eyes are open but still sensitive to light and we still must keep their bed dark and try to keep lights dim or cover their eyes when we need bright lights. They will likely need some help breathing and will need to be fed through a tube until they can learn to eat by bottle.
A 28 week baby on BiPap (a machine providing a small amount of positive pressure to the lungs)
The later-term preemies are about 32-35 weeks. These babies may need some respiratory support and will need help learning to eat by bottle or breast, but hopefully will not have too many other issues to overcome. They usually spend a much shorter time in our NICU and have few long-term medical complications. These babies are usually 3, 4, and 5 lbs or more. They may need a little short-term help breathing, but can usually breath on their own after a few days or a week. They will need a little help feeding through a tube but usually learn to eat by bottle pretty quickly. They need a little help staying warm and somewhat dimmer lights, but can be in a crib quickly and have less light sensitivity.
Modern NICUs have many great treatments and equipment to help these little babies develop and get the chance to do lots of teaching to the parents. The job is tough, but extremely rewarding and I love it!
(Note: the pictures above were found on google images or permission was given by the parents)