In general, outcomes for premature babies are very good. Before the development of Neonatal Intensive Care Units (NICUs), many premature babies did not survive. The introduction of incubators, mechanical ventilation, and other technologies and medical techniques, as well as a more complete understanding of newborn baby physiology, have increased premature baby survival dramatically. As a result, some premature babies who would have died in the past now survive, but may have lifelong problems. Medical professionals make this distinction using the words “morbidity” and “mortality.”
Mortality and morbidity
Mortality is the rate of death or the number of premature babies admitted to an NICU who do not survive compared to those who do. As noted above, the mortality rate of premature babies has dramatically improved over the last 20 years or so.
The overwhelming majority of babies with access to the modern technology and medical techniques available in the NICU now survive. At the same time, there are limits to the medical technology and techniques available in the NICU; some babies who are born too soon are too small to either save at all or save without serious disability or morbidity.
Morbidity is the number of babies who survive but with lasting complications, compared to the number who survive with no lasting complications. These complications may include problems with learning and behaviour, movement and coordination, vision, hearing, and other problems.
Although many premature babies go on to live normal, healthy lives, the success rate in this regard is not as overwhelming as the dramatic improvement in mortality. In fact, the two statistics are related: medicine has become very successful at keeping premature babies alive, especially the extremely premature, who tend to have more complications than other premature babies.
In general, outcomes are related to:
- the gestational age, or the number of weeks a premature baby spent in the womb
- the weight of the baby at birth
- the number and scope of medical complications
The spectrum of prematurity: mild, moderate, and extreme
Based on their gestational age and birth weight, premature babies are placed into loosely defined categories of mild, moderate, and extreme prematurity.
- Mild prematurity refers to babies who are born between 33 and 36 completed weeks gestational age and/or have a birth weight between 1500 and 2500 g (between about 3 lbs 5 oz and 5 lbs 8 oz).
- Moderate prematurity refers to babies who are born between 28 and 32 completed weeks gestational age with a birth weight ranging between 1000 and 1500 g (between about 2 lbs 3 oz and 3 lbs 5 oz).
- Extreme prematurity refers to babies who are born before 28 completed weeks gestational age or who have a birth weight of less than 1000 g (less than about 2 lbs 3 oz).
Mildly premature babies do better than moderately premature babies, who in turn do better than extremely premature babies. This makes intuitive sense: barring other complications not due to prematurity, the longer a baby has spent in the womb, the more developed their organs are and therefore the more prepared they are for the challenges of the outside world.
Statistics and the individual baby
As specific complications are addressed in this site, outcome statistics specific to that condition are provided where appropriate. However, mortality and morbidity statistics are based on group data and do not take into account the individual baby.
The body is very much an interconnected system. The ways in which two or more complications affect each other can have a huge impact on morbidity and mortality, making the course and outcomes of illness difficult to predict.
Some, though few, extremely premature babies do surprisingly well and go on to thrive as healthy children. Conversely, some mildly premature babies who are expected to do well develop complications and lifelong problems or do not survive at all.
This is not to say that statistics and outcome data should be ignored; this information is extremely useful to physicians and other medical professionals who are devoted to producing the best possible outcomes for premature babies. Mortality and morbidity data can help medical staff anticipate and predict problems that have not surfaced yet, and allow for pre-emptive or preventive treatment that will benefit the baby.
Outcome statistics are not definitive. Rather, they are a guide to be used by medical professionals, and parents and families. Given all the possible combinations of complications premature babies may face, making an actual outcome prediction can be complex, even impossible. At other times, a particular complication or series of complications may make outcome prediction, both good and poor, more simple.
For this reason, staff at the NICU will speak in terms of probabilities: for example, they may say that 75% of babies with a specific condition will recover completely without lifelong complications. Predicting an individual baby’s outcome cannot be done with absolute certainty.