Children who are preterm, are small for gestational age (SGA), or have low birthweight (LBW), defined as birthweight <2,500 g, often exhibit a wide range of developmental problems (Hack & Fanaroff, 1999
; McCormick, 1985
; Mutale, Creed, Maresh, & Hunt, 1991
). During school-age years, for example, these children were found to have higher incidences of behavior problems (Gray, Indurkhya, & McCormick, 2004
; Hack, Taylor, Klein, & Eiben, 1994
), emotional problems (Cheung, Ma, Machin, & Karberg, 2004
), cognitive deficits (Hack et al., 1994
; Litt, Taylor, Klein, & Hack, 2005
), and learning difficulties (Brooks-Gunn, Gross, Kraemer, Spiker, & Hapiro, 1992
; Rickards, Kelly, Doyle, & Callanan, 2001
; Saigal, Pinelli, Hoult, Kim, & Boyle, 2003
; Saigal, Rosenbaum, Szatmari, & Campbell, 1991
; Saigal & Streiner, 1995
) compared to controls. However, we still know little about the risks that children born near-term face with regards to their learning-related abilities and educational attainment (near-term birth, or NTB, is defined as birth of a child between 33 and 37 weeks of gestation).
NTB as a subgroup of preterm birth has recently attracted attention (Barrington & Finer, 1997
; Maisels & Newman, 1998
; Raju, 2006
; Wang, Dorer, Fleming, & Catlin, 2004
) partly because of an increase in its prevalence, from 7.3% in 1992 to 16% in 2002, or 71% of all preterm births (<37 weeks; National Center for Health Statistics, 2005
). Reasons for this increase include advanced medical interventions in pregnancies (Villar et al., 2004
), cesarean delivery and labor induction (Raju, 2006
), having children later in life due to lifestyle changes (Mathew & Hamilton, 2002
), and an increased rate of multiple births from assisted fertilization (Lee, Cleary-Goldman, & D’Alton, 2006
; Russell, Petrini, Damus, Mattison, & Schwartz, 2003
). Recent studies have also found an increase in the risk for neonatal and postnatal morbidity and mortality (Kramer et al., 2000
; Tomashek et al., 2002
) in this subgroup—risks often neglected, as near-term babies look healthy despite their immaturity (Wang et al., 2004
NTB babies are usually considered to be at low risk for later neurodevelopmental problems, and so are unlikely to be monitored and followed up (Huddy, Johnson, & Hope, 2001
). Though the number of studies evaluating problems beyond early childhood in NTB children is still small, evidence suggest that poor outcomes in infancy and early childhood may not be limited to those born very preterm (<32 weeks) and extremely preterm (<28 weeks), and that NTB should be followed and diligently evaluated and monitored, and regarded as a biological risk (Raju, 2006
). This information would have direct bearing on decision making by obstetricians regarding interventions for early delivery.
Huddy et al. (2001
) reported that approximately one third of children born between 32 and 35 weeks of gestation had difficulties in writing, fine motor skills, and mathematics; about one-fifth had difficulties in reading and fine motor skills; and a quarter received nonteaching assisted help at school. Kirkegaard et al. (2006
) evaluated the effects of LBW in a population-based sample of 5,319 children who were born after 33 weeks of gestation. They found that LBW children, after adjusting for gestational age, that is, a crude proxy for SGA, were at a marginally increased risk for reading [odds ratio (OR) = 1.9, 95% confidence interval (CI) = 0.8–4.2] and spelling disabilities (OR = 2.2, 95% CI = 0.96–4.8), and a significantly increased risk for arithmetic disability (OR = 4.5, 95% CI = 1.4–15.0) compared to children with a birthweight (BW) between 3,500 and 3,999 g. Kirkegaard et al. found gestational, age-adjusted BW, which is often used as a crude proxy of intrauterine growth restriction (IUGR), was a risk factor for learning disabilities at age 10. They also found a modest increased risk for spelling disability among NTB relative to those born normal term. However, it is not clear whether NTB who also have psychosocial risks, such as poverty, are at a significant increased risk for learning problems.
Poverty is recognized as a risk factor for childhood cognitive functioning and possibly later educational attainment (Ackerman, Brown, & Izard, 2004
; Botting, Powls, Cooke, & Marlow, 1998
; Klevanov & Brooks-Gunn, 2006; Shaw, Winslow, Owens, & Hood, 1998
). Bradley, Mundfrom Whiteside, Casey, and Barrett (1994
) refer to poverty to as double jeopardy since the risks tend to be a cause, or are the consequence of, interrelated biological and psychosocial disadvantages that lead to more serious consequences (Watson, Dirby, Kelleher, & Bradley, 1996
). While childhood poverty has been found to be a risk factor for lower cognitive function among school-aged children, it is not known whether poverty is especially deleterious for those at biological risk such as from preterm birth and SGA. Since poverty brings multifaceted disadvantages, including financial, emotional, psychological, and social disadvantages, which could be more extreme for those with biological risks (even a milder form of the risk such as NTB), it may be a possible amplifier for the risk of learning-related problems in childhood and educational attainment in adulthood. For instance, poverty can certainly limit learning resources and opportunities (Linver, Brooks-Gunn, & Kohen, 2002
; Saigal, Hoult, Streiner, Stoskopf, & Rosenbaum, 2000
; Watson et al., 1996
). Parents who live in poverty may be less likely to provide a stimulating environment, where their offspring could gain hands-on learning experiences as poverty and parental educational level is highly correlated (Brooks-Gunn et al., 1992
). Poverty can also create frustration among parents and make it difficult for parents to provide optimal care, bonding, and support to their offspring (McAdoo, 1988
; Watson et al., 1996
). Further, it can prevent parents from providing an optimal physical environment such as adequate hygiene and safe, uncrowded physical space. It is possible that NTB children have greater need for these resources than non-NTB children.
Furthermore, while it is clear that there are intercorrelations among perinatal risks, childhood poverty, and child cognitive functioning and learning abilities, no prior study has examined these factors simultaneously to understand through what mechanism these risk factors affect educational attainment in adulthood. The delineation of possible interrelationships among those factors, through the examination of the mediating effect of childhood learning-related abilities and the moderating effect of poverty, could help identify who is at increased risk for learning problems and lower educational attainment among NTB children. Doing so will allow us to advance our knowledge on modifiable risk factors.
We hypothesized that (a) NTB and SGA are independently associated with a lower level of educational attainment in adulthood; (b) NTB and SGA may be early determinants of educational attainment in adult life mediated though decreased childhood learning-related abilities (IQ, reading, spelling, and arithmetic); and (c) the adverse effect of NTB and SGA on childhood learning-related abilities and adult educational attainment may be stronger among children who grew up in poverty.