While it is not always possible to say with 100% certainty which premature babies will have ongoing problems, it is known that some babies born prematurely are more at risk than others. Sometimes, the likelihood of an ongoing disability can be predicted. In general, when this is possible, it is because the child either faced many or very few challenges as a premature baby. For example, a baby born very prematurely, who had several complications, perhaps involving the brain, will almost certainly face life-long disability issues. At the other end of the scale, a baby born only mildly premature who had no complications will likely be spared life-long issues.
The spectrum of prematurity and risk of disability
In general, it is the smallest and most premature babies who are at risk for ongoing or life-long disability. Premature babies are categorized into three groups: extremely premature, moderately premature, and mildly premature.
Mild prematurity or "late preterm: babies as they are sometimes called, refers to babies who are born between 33 and 36 completed weeks gestational age with a birth weight between 1500 and 2500 g (between about 3 lbs 5 oz and 5 lbs 8 oz). Although these babies are less mature than full-term babies, they have a greater than 95% survival rate.
Their long-term prospects are not quite as high as full-term babies. In follow up, these infants often have learning problems and early recognition and diagnosis of this may be helpful in avoiding longer-term school difficulties
Moderate prematurity refers to babies who are born between 28 and 32 completed weeks gestational age with a birth weight range between 1000 and 1500 g (between about 2 lbs 3 oz and 3 lbs 5 oz). About two-thirds of these premature babies will develop normally. Another 20% will have mild or moderate disabilities, and about 15% of these babies will suffer from severe disabilities.
The more premature the birth within this category, the higher the incidence of long-term problems. But even younger and sicker babies within this age group are at minimal risk, unless they had severe growth delay in the womb, show signs of brain damage on a head ultrasound, or have severe lung damage. And even some premature babies with these risk factors turn out fine.
Extreme prematurity refers to babies who are born before 28 completed weeks gestational age with a birth weight of less than 1000 g (less than about 2lbs 3oz). Many of these babies, especially those born around 25 weeks or less, will not survive. In this category as a whole, only about one-third of surviving babies born extremely prematurely will grow up normal. Another third will have mild or moderate disabilities, and about one-third will have severe disabilities.
It should be noted that within this group, those born at 28 weeks are less likely to have disabilities than those born at 25 weeks or less. When babies are born this early, every extra day inside the womb reduces the risk of long-term problems in a significant way.
While the vast majority of deaths due to prematurity are now prevented, the survival rate for extremely premature babies born at a gestational age of 25 weeks or less remains at about 50%. Additionally, of those extremely premature babies who do survive, about half will have a disability of some kind, often severe.
Other risks for ongoing problems
Birth weight and degree of prematurity are not the only risk factors for an ongoing disability. Various complications a premature baby may have experienced immediately following birth can also put a child at risk as he grows. In addition to complications that can lead directly to specific physical disability, for example, retinopathy of prematurity as a risk for vision problems, other complications are also risk factors. The following conditions have been linked to longer-term behavioural, intellectual, and educational problems.
- the socio-economic situation of the parents of a premature baby
- the race and sex of the child
- circumference of the head at birth
- the use of ventilation
- the occurrence of brain injury
- delayed or smaller than average head growth