People who were born small for their gestational age are slightly less likely to perform well in school, are less likely to hold professional or managerial jobs and report lower weekly incomes than people who were normal-birth-weight, according to a study that followed participants from birth to age 26. However, at age 26, the two groups are equally likely to be married and working, and equally satisfied with how their lives have turned out.1
To assess the functional effects of being small for gestational age (defined as having a birth weight less than the fifth percentile for age at term), the investigator analyzed data on infants born in the United Kingdom during the period April 5-11, 1970, who were followed up at ages five, 10, 16 and 26. Infants were excluded if they had congenital abnormalities, which can influence developmental outcomes, or if they were born preterm. The resulting sample consisted of 1,064 infants who were small for gestational age and 13,125 normal-birth-weight infants, who served as the comparison group.
There were some significant differences in the demographic characteristics of the two birth-weight groups. For example, 24% of normal-birth-weight infants had at least one parent who was a professional, compared with 15% of infants who were small for gestational age. Ten percent of infants who were underweight at birth were born to single mothers, compared with 6% of normal-birth-weight infants; 8% and 6%, respectively, were born to women aged 18 or younger.
Follow-up data included participants' standardized test scores, teacher evaluations and, for adolescents and adults, responses to questionnaires on emotional and social development. At ages 16 and 26, participants responded to questions about their self-perception. At age 26, they also reported on their marital and employment status and income. The data were adjusted for sex, parental social class and region of birth. The proportion of the entire sample who responded was 93% at age 5, 80% at age 10, 72% at age 16 and 53% at age 26.
At ages five, 10 and 16, participants who had been small for gestational age had lower scores than normal-birth-weight participants on standardized tests measuring a range of academic and developmental outcomes. However, the differences between the two groups were very small (0.1-0.4 standard deviations), and scores on some measures were not significantly different: Reading scores at age 10 and spelling and word recognition scores at age 16 were similar in both groups.
Teachers' ratings of the general knowledge and academic achievement of 10-year-olds who had been small for gestational age were significantly lower than their ratings for those who had been normal-birth-weight. Twenty-one percent of 10-year-olds who had been underweight at birth were rated by their teachers to be "above average or well informed," compared with 31% of those who had been normal-weight.
When they were 16, youths who had been small for gestational age were less likely than others to be rated by their teachers as being in the top 15th percentile of their class (13% vs. 20%) and in the highest grade levels in math (16% vs. 28%). In addition, adolescents who had been small for gestational age were more likely than their normal-birth-weight peers to have been placed in special education (5% vs. 2%). Although adolescents who had been small for gestational age were more likely than other adolescents to report difficulties at school (49% vs. 40%), the two groups were similar on measures of social and emotional development, such as their number of friends, levels of family stability and happiness, and interest in recreational and social activities. Virtually all of the teenagers in both groups described themselves as friendly, popular and loving; about three-fifths in each group considered themselves angry or shy.
At age 26, participants who had been underweight at birth were less likely than those who had had a normal birth weight to hold professional or managerial jobs (9% vs. 16%) and were more likely than others to work as unskilled, semiskilled or manual laborers (34% vs. 28%). Those who had been small for gestational age reported a lower weekly income than did people who had had a normal birth weight. However, there was no difference between the two groups in several areas. Participants in both groups had attended school until they were 18 and worked approximately 40 hours per week; more than nine in 10 were employed, and about one-third were married. Furthermore, the two groups were equally satisfied with their lives, and on average, 52% of participants in both groups perceived their standard of living to be better than others'.
The investigator acknowledges that the findings may be biased as a result of the low follow-up rate at age 26. However, he contends that this study presents the most comprehensive picture to date of the long-term outcomes of infants who were small for gestational age since previous research focused on testing cognitive development and did not measure social and emotional outcomes. In discussing the policy implications of his findings, the investigator observes that early intervention programs such as Head Start can enhance cognitive development among disadvantaged preterm and full-term infants. These programs, he suggests, could also benefit children who had been small for gestational age, who may have functional impairment. In conclusion, he recommends that children who were underweight at birth be provided with "an enriched environment to minimize the long-term negative effects."--B. Brown
1. Strauss RS, Adult functional outcome of those born small for gestational age: twenty-six-year follow-up of the 1970 British birth cohort, Journal of the American Medical Association, 2000, 283(5):625-632.