Risks and causes of mortality among low-birthweight infants in childhood and adolescence

The purpose of the study was to estimate the risks of mortality among infants with low birthweight (LBW, <2500 g) during their childhood and adolescence using a prospective cohort design. A total of 341 249 livebirths were registered in the 1985 Taiwan Birth Registry. We identified the 11 701 LBW singletons and randomly selected the same number of normal-birthweight (NBW) singletons. Study subjects of both LBW and NBW groups were linked, through the individual's unique personal identification number, to the Taiwan Death Registry to identify those who died between 1985 and 2003. Using the life-table method, we calculated the age-specific and cumulative survival rate for both LBW and NBW groups. We used Cox's proportional hazard model with adjustment for potential confounders to estimate the age-specific hazard ratio (HR) of mortality. Age-specific causes of mortality were presented for both groups. The result showed that the cumulative survival rate over an 18-year period for the LBW and NBW subjects was estimated at 95.83% and 99.37%, respectively. Significantly increased adjusted HR of mortality associated with LBW was limited to ages <1 year (boys: 8.99; girls: 8.29) and 1-4 years (boys: 2.19; girls: 2.25). Conditions originating in the perinatal period and congenital anomalies were the most prevalent cause of death among LBW and NBW, respectively. Between ages 1 and 18 years, injury and poisoning became the top ranked causes of death irrespective of birthweight and gender. Although there were small numbers of congenital anomalies, they were still a leading cause of death for LBW subjects, but not for NBW subjects, at ages 5-18 years. The LBW subjects were also likely to suffer from respiratory causes at 5-18 years. This study suggested, therefore, that LBW infants tended to have significantly elevated mortality rates under the age of 5 years, and were vulnerable to more non-injury deaths in their childhood and adolescence.