Very-low-birth-weight individuals (those weighing less than 1,500 g at birth) experience educational and intelligence deficits that last into young adulthood, according to data from a longitudinal study in Ohio.1 For example, they have significantly decreased odds of graduating from high school by age 20 and increased odds of having an IQ in the subnormal or borderline range. However, at age 20, women who were very-low-birth-weight are less likely than their normal-birth-weight peers to report having used alcohol or drugs within the previous year, ever having had sexual intercourse, ever having been pregnant and ever having been involved in a live birth. Very-low-birth-weight men are less likely than control males to report ever having violated a law, not including traffic laws.
The study is based on a cohort of children who were born weighing less than 1,500 g and were admitted between 1977 and 1979 to a health facility in Cleveland. Researchers initially collected physical, behavioral and demographic data from 256 very-low-birth- weight participants and 366 controls who had a normal birth weight at age eight; 242 participants and 233 controls were interviewed again at age 20. The researchers also collected data on maternal characteristics (marital status, education, and social and demographic information) at the time of the child's birth and eight years later.
When participants reached age 20, the investigators obtained data on their educational attainment, current enrollment in an educational program and health status by using a detailed interview; high school graduation was confirmed by means of school records. The researchers also ascertained the participants' intelligence, verbal comprehension, perceptual-organizational skills and academic skills. They measured risk-taking behavior during the previous 12 months with a self-administered questionnaire, which included a substance abuse checklist, a sexual experience scale and questions regarding contact with the police.
The investigators performed univariate and multivariate analyses to compare very-low-birth-weight participants with controls. The multivariate analyses (logistic and multiple linear regression for dichotomous and continuous outcomes, respectively) controlled for social and demographic variables; separate analyses were performed for men and women to determine if gender significantly affected any outcomes.
Very-low-birth-weight individuals had significantly less educated mothers than controls: When the children were eight, 17% of the mothers of very-low-birth-weight individuals had not graduated from high school, compared with 11% of those of controls. Maternal marital status at eight years of follow-up and maternal race did not differ significantly between the two groups.
Overall, a significantly greater proportion of very-low-birth-weight individuals than of controls suffered from chronic health conditions at age 20 (33% vs. 21%). Neurosensory conditions were significantly more common among very-low-birth-weight men and women (9% and 11%, respectively) than among controls (0-1%). More than one-third (36%) of very-low-birth-weight females had at least one chronic health condition, a significantly larger proportion than among control females (20%).
In multivariate analyses of educational attainment, very-low-birth-weight individuals were significantly less likely than controls to have graduated from high school by age 20 (odds ratio, 0.6), and those who had graduated had done so at an older mean age (18.2 years vs. 17.9 years). In addition, very-low-birth-weight participants were significantly more likely not to be currently enrolled in an educational program (odds ratio, 1.5). Very-low-birth-weight men had significantly decreased odds of currently being enrolled in postsecondary study (0.4) or in a four-year college (0.2); among women, there were no significant differences in educational attainment by birth weight.
The researchers found that birth weight status was significantly associated with IQ: Compared with controls, very-low-birth-weight individuals had half the odds of having an IQ in the normal range (85 or greater); they had 1.7 times the odds of having a borderline normal IQ (70-84) and 4.0 times the odds of having a subnormal IQ (70 or lower). Very-low-birth-weight men were significantly more likely to have a borderline IQ (odds ratio, 2.3) and less likely to have a normal IQ (0.3) than were control males. These differences remained significant even when the analyses were restricted to participants without neurosensory conditions. There were no significant differences in intelligence found between very-low-birth-weight women and control females.
It surprised researchers to find that very-low-birth-weight individuals reported less risk-taking behavior by age 20 than controls. Very-low-birth-weight women were less likely to have used alcohol or marijuana within the previous year, and were less likely to ever have had sexual intercourse or been involved in a pregnancy or live birth (odds ratios, 0.3-0.6). Very-low-birth-weight men had half the odds of control males of ever having violated a law, not including traffic laws (0.5).
Although previous studies have shown only that very-low-birth-weight individuals encounter educational disadvantage during youth, the researchers suggest that "this disadvantage extends into young adulthood." They also conclude that it is likely that "men who had very low birth weight will lag behind their normal-birth-weight peers in their ultimate educational and occupational achievement." That very low birth weight was significantly associated with lower rates of risk-taking behavior was not one of the researchers' starting hypotheses. They suggest that this phenomenon "may result from increased parental monitoring of very-low-birth-weight children."
1. Hack M et al., Outcomes in young adulthood for very-low-birth-weight infants, New England Journal of Medicine, 2002, 346(3):149-157.