摘要：Objectives. We assessed whether the association between low birthweight and early childhood asthma can be explained by an extensive set of individual- and neighborhood-level measures. Methods. A population-based sample of children born in large US cities during 1998–2000 was followed from birth to age 3 years (N=1803). Associations between low birthweight and asthma diagnosis at age 3 years were estimated using multilevel models. Prenatal medical risk factors and behaviors, demographic and socioeconomic characteristics, and neighborhood characteristics were controlled. Results. Low-birthweight children were twice as likely as normal birthweight children to have an asthma diagnosis (34% vs 18%). The fully adjusted association (OR= 2.36; P <.001) was very similar to the unadjusted association (OR= 2.48; P <.001). Rates of renter-occupied housing and vacancies at the census tract–level were strong independent predictors of childhood asthma. Conclusions. Very little of the association between low birthweight and asthma at age 3 can be explained by an extensive set of demographic, socioeconomic, medical, behavioral, and neighborhood characteristics. Associations between neighborhood housing characteristics and asthma diagnosis in early childhood need to be further explored. Childhood asthma has nearly doubled in the last 2 decades to become one of the most common chronic childhood conditions in the United States, from 3.7% of children in 1980 to 6.9% in 1995. 1 , 2 Although family history of asthma and atopy is highly predictive of asthma in children, 3 most researchers agree that environmental factors must play an important role, because genetic variation alone cannot explain such a steep increase in childhood asthma rates. 3 – 5 Childhood asthma is associated with increased rates of doctor visits, hospitalizations, school absenteeism, parental work absenteeism, child activity limitations, and child disability. 6 – 8 Children living in inner-city neighborhoods are at especially high risk for asthma. 9 , 10 The rates of low birthweight (< 2500 g) and very low birthweight (< 1500 g) have also increased in the US to 7.8% and 1.5%, respectively—the highest levels in 3 decades. The increases are largely, but not entirely, attributable to an increase in the prevalence of multiple births. 11 As a result of substantial advances in neonatal care technology, low-birthweight infants are much less likely than they were in 1980 to die before their first birthday. 12 Low-birthweight infants who survive, particularly those who are very low birthweight, are at high risk for respiratory disorders. 12 A number of studies have found strong associations between low birthweight and subsequent poor lung function, 13 – 26 although not all have focused specifically on children or asthma. The mechanisms underlying the association are not clearly understood. The uterine environment may play a role, through nutritional intake and development of the immune and respiratory systems. 26 , 27 Neonatal respiratory support interventions may contribute to disturbances in subsequent pulmonary function. 15 The observed associations between low birthweight and childhood asthma are also thought to reflect, at least in part, poverty-related factors such as inner-city residence and poor housing quality, which have been associated with both conditions. 10 , 28 – 35 We analyzed a sample of children born in large US cities between 1998 and 2000 and followed the children through age 3 years. We used this sample to assess the extent to which the association between low birth-weight and childhood asthma in the urban population can be explained by an extensive set of demographic and socioeconomic characteristics, maternal medical risk factors, and prenatal behaviors that are associated with both conditions. We also explored the extent to which neighborhood characteristics explain the association.
