The survival of a baby born before 37 weeks of pregnancy depends more upon the weight of the baby than the actual number of weeks of pregnancy. Babies under 500g have only a 40% chance of survival, under 1000g a 65% chance, and over 1500g a nearly 100% chance of survival. These figures are for the best hospitals in developed countries, but babies born prematurely in remote areas will have a far lower survival rate.
The problems that very premature babies face include liver failure and jaundice, inability to maintain body temperature, immature lungs, inability to maintain the correct balance of chemicals in the blood, patent ductus arteriosus, increased risk of infection due to an immature defence system, bleeding excessively, and eye problems including blindness. The smaller the baby, the greater the problems, and the more intensive the care required from specialised units in major hospitals.
The activity and processes of immature babies must be monitored carefully. Tubes and leads to and from the infant may appear to overwhelm it but are necessary to monitor the heart and breathing, supply oxygen, assist breathing in some cases, feed the baby, drain away urine, keep the temperature at the correct level, and maintain the correct chemical balance in the blood.
Even some of the treatments to help these babies can have serious complications. Many require oxygen to allow them to breathe, but too much oxygen can cause a condition called retrolental fibroplasia that damages the retina (light sensitive area) at the back of the eye to cause permanent blindness. Premature babies also progress better if their intensive care nursery is darkened and quietened for the twelve night hours.
A baby born prematurely will be a little later in reaching the milestones of infancy and should have routine immunisations in the first six months slightly delayed. The delay is roughly the number of weeks of prematurity before 37 weeks (ie. a baby born at 31 weeks is 6 weeks before 37 weeks, and can expect its milestones and vaccinations to be delayed by 6 weeks). The delay is halved by the time the child reaches six months of age, and disappears completely by one year of age.