Charge to Participants and Workshop Scope*
Donald R. Mattison
Preterm birth is one of the more complex and challenging chronic diseases that have captured the attention of the life sciences and environmental health sciences. Worldwide, preterm births—those that occur before 37 weeks of gestation—constitute 5 to 12 percent of all births, accounting for more than 400,000 births each year. In the United States alone, more than 1,200 babies are born prematurely every day, and the rate of prematurity in this country is increasing.
Our interest in preterm birth springs from the fact that children who are born too early suffer adverse consequences. One potential consequence of prematurity is respiratory distress syndrome, which impairs the areas of the lung over which oxygen transport and diffusion take place. Another possible consequence is brain damage, often from intraventricular hemorrhage and periventricular cysts, which can lead to neurodevelopmental problems. In industrialized and nonindustrialized countries alike, preterm birth is linked to morbidity and mortality. Clearly, we need to investigate the causes of this condition.
In the past, prematurity was defined by the infant’s birth weight—less than 2,500 grams. Recently, we have recognized that weight alone does not adequately characterize the risks faced by premature infants. Currently, characterizing the status of a child at birth involves both birth weight and gestational length. Infants of greatest concern are those with a gestational length of less than 32 weeks and a birth weight of less than 1,000 grams, because they suffer the most severe consequences.
During this workshop, we will place preterm birth in a framework similar to
that for diseases such as diabetes or hypertension, which are influenced by multiple genetic, social, personal, and environmental factors. Although the biological reasons for differences across ethnic background have not been identified, certain populations have a substantially greater risk for prematurity, and prematurity rates vary by region across the country. For example, substantial differences between African Americans and Caucasians have been found in preterm birth rate and infant mortality associated with prematurity (Healthy People 2010). These differences are difficult to understand biologically, suggesting that environmental factors play a role. We must consider carefully what these environmental factors might be, because understanding the factors that influence these variations will help us develop a better sense of the cause of prematurity and strategies for preventing it.
Among the five leading causes of infant mortality, two—low birth weight and respiratory distress syndrome—are associated with being born too early. The economic costs of preterm birth are substantial, both at the beginning of life and throughout its course. Data from the Agency on Healthcare Research and Quality reveal that two of the five most expensive hospital conditions in the United States in 1997 were associated with prematurity (AHRQ, 1996). Respiratory distress syndrome, the most expensive condition, had a mean hospital charge of $68,000 and a length of stay of more than 24 days. Low birth weight did not lag not far behind, with a $50,000 mean hospital charge and a length of stay of more than 21 days. These data are for children who are discharged alive. We have begun experimenting with community interventions to try to understand how we can influence these outcomes.
Preterm deliveries fall into three broad categories or pathways. The first category is medically indicated early deliveries—those necessitated by maternal or fetal factors. In such cases, it is believed that whatever the potential consequences of prematurity may be, early delivery is much safer for both the mother and the child. The other two categories—early deliveries due to spontaneous preterm ruptured membranes and those due to spontaneous preterm labor—may respond to intervention. As ones knowledge of etiology improves, all of these pathways may yield to prevention. Some participants have asked that we consider the possibility that early deliveries in all three categories are modifiable. Some have suggested that the factors influencing early delivery in each of these categories may be the same. Thus, we need to examine whether the strategies for preventing early delivery in one category may prevent conditions associated with another category. One charge for this workshop is to consider why we have created separate categories, which may be artificial, and how prevention strategies may affect all categories simultaneously.
An underlying truth regarding prematurity that relates to the issue of separating individual, environment, and genetic factors is the unfortunate observation that the best predictor of having a preterm birth is having experienced one previously (Mattison et al., 2001). The risk increases with each successive preterm
birth. For example, if a woman’s first child is born at term, her risk for preterm delivery of a second child is about 4 percent. However, if her first baby is born prematurely, her risk for preterm delivery of a second child jumps to 17 percent. If her first and second children are born prematurely, her risk for preterm delivery of a third child rises to almost 30 percent. Looking deeply into this situation may provide a key to understanding the factors associated with prematurity.
Some factors influencing prematurity have already been identified. Most studies have focused on the individual and have set out to explore the characteristics of individuals that might confer risk for preterm delivery, some of which may be modifiable and some of which may not. Skin color and age are examples of characteristics that cannot be changed. The consequences of socioeconomic influences, which might persist across a life span, may respond to intervention at some level, but they may not be modifiable to any great extent within the individual.
Emerging data suggest that other factors play a role in prematurity. Some of these data point to environmental factors, and these findings bring us back to the traditional public health paradigm in which we must distinguish between social, biological, and environmental factors and try to understand how they interact in the condition of prematurity. Within this context, the specific goals of this workshop are to
summarize the clinical and epidemiological aspects of prematurity;
create an understanding that exposures to environmental chemicals can alter gestation length;
summarize cellular, molecular, and genetic aspects of control of preterm delivery;
recognize that current in vivo and in vitro toxicological testing models are inadequately designed to capture the data showing whether chemicals influence gestation length;
understand that, because preterm delivery is a substantial public health concern, toxicological approaches have to be developed to improve our understanding of the impacts of the chemicals on gestational length; and
recognize that a multidisciplinary approach is needed to better clarify the mechanism underlying gestational length
Our overall goal is to begin to summarize the current understanding of prematurity from the particular perspective that each of us brings to this topic and to stimulate cross-disciplinary interaction.