Socioeconomic disadvantage, fetal environment and child development: linked Scottish administrative records based study

The cognitive and emotional development of children growing up in circumstances of socioeconomic disadvantage is more likely to be abnormal compared to children raised in more advantaged families [1]. This association has been noted for a range of different developmental attributes including gross motor skills [2], vision and fine motor skills [3], social development [4] and hearing and language development [5]. Atypical child development outcomes are also associated with low birthweight (LBW) [6] including significant motor impairment [7], conductive hearing loss [8], and a wider spectrum of social and behavioural difficulties [9, 10]. Infants born preterm are more likely to have development problems. A large proportion of extremely preterm children will experience significant development delay, cognitive impairments, learning disabilities, and behavioural and emotional problems [11]. Preterm children are also more likely to have fine motor development problems [12].

The aim of this study was to examine the extent to which differences in fetal environment mediate the association between socioeconomic position and child development. Few studies have simultaneously evaluated the role of other determinants of child development [13]. Previous studies have identified that birthweight is associated with family socioeconomic position with the children of parents in manual occupations being more likely to have low or very low birthweight [14, 15]. Our measure of fetal environment include a range of variables which represent pregnancy and delivery complications (including birthweight and preterm birth), mother’s behaviour and the physical condition of the new born child. Birthweight is associated with family socioeconomic position [14, 15]. We hypothesised that children born to disadvantaged parents would be more likely to have developmental abnormalities but that this would be partially mediated by a poorer fetal environment among more disadvantaged families.

Table 1 reports the characteristics of the baseline sample in frequency of reviews. 114,928 Reviews of gross motor and hearing and language development were recorded for 32,238 individuals. The number of reviews of vision and fine motor and social development was lower (93,481 reviews) because these were not reviewed at the 6–8 week review (see Additional file 1: Table S1). There are notable differences in parental socioeconomic position between children with abnormal or doubtful development compared to those with normal development across all indicators. Children with abnormal or doubtful development tend to have parents in less advantaged occupational positions (for all four indicators the p-value is less than 0.001, based on Cuzick’s nonparametric test for trend in ordinal data³). A similar pattern exists by parental highest qualification.

Table 2 reports models predicting gross motor, hearing and language, vision and fine motor, and social development. Two models are estimated for each outcome which include measures of social background plus fetal environment.⁴ The patterning of socioeconomic disadvantage varies by child development measure (see Fig. 2). Parental NS-SEC was not associated with gross motor but was predictive of hearing and language, vision and fine motor, and social development. Before adjustment for fetal environment, children whose parents were in semi-routine (NS-SEC 6; OR = 2.18; CI = 1.49, 3.19) and routine occupations (NS-SEC 7; OR = 2.34; CI = 1.56, 3.52) were more likely to have abnormal or doubtful vision and fine motor development than those with parents in higher managerial or professional occupations (NS-SEC 1.1).

Deficiencies in hearing and language and social development were noted for a wider range of parental NS-SEC classes than for vision and fine motor development. Children whose parents were small employers and own account workers (NS-SEC 4; OR = 1.53; CI = 1.19, 1.96), in lower supervisory and technical occupations (NS-SEC 5; OR = 1.55; CI = 1.23, 1.95), semi-routine occupations (NS-SEC 6; OR = 1.70; CI = 1.37, 2.11) and routine occupations (NS-SEC 7; OR = 1.67; CI = 1.32, 2.12) were more likely to have abnormal or doubtful hearing and language development than those with parents in higher managerial or professional occupations, prior to adjustment for fetal environment (NS-SEC 1.1). Social development followed a similar pattern.

For all four development measures, children with parents that had never worked or were long-term unemployed were more likely to exhibit abnormal or doubtful development than those with parents in higher managerial professional occupations in models which were unadjusted for fetal environment. This was true for gross motor (OR = 1.70; CI = 1.03, 2.80), hearing and language (OR = 2.14; CI = 1.63, 2.80), vision and fine motor (OR = 3.60; CI = 2.32, 5.58), and social development (OR = 4.12; CI = 2.46, 6.90). Children with parents without educational qualifications were more likely than those who parents had a degree to exhibit abnormal or doubtful gross motor (OR = 1.62; CI = 1.21, 2.17), hearing and language (OR = 1.82; CI = 1.55, 2.13), vision and fine motor (OR = 2.40; CI = 1.86, 3.09), and social development (OR = 2.08; CI = 1.56, 2.78) in models which did not adjust for fetal environment.

Infants born in the 0-3rd gestational-age specific percentile for birthweight, were more likely to experience abnormal or doubtful gross motor development (OR = 2.92; CI = 2.05, 4.15), hearing and language (OR = 1.70; CI = 1.38, 2.09), vision and fine motor (OR = 2.08; CI = 1.51, 2.87), and social development (OR = 2.79; CI = 1.94). The effect size was smaller for infants born in the 4th–10th percentiles. We did not observe a greater risk for infants whose gestational-age specific birthweight percentile is above average. Similar results are reported when the analysis was performed using absolute measures of birthweight (see Additional file 1: Table S4). There was also clear association between pre-term birth and gross motor development (OR = 2.65; CI = 1.97, 3.56), hearing and language (OR = 1.75, CI = 1.49, CI = 2.06), vision and fine motor (OR = 2.21; CI = 1.70, 2.86), and social development (OR = 1.98; CI = 1.48, 2.63) (Table 2).

The inclusion of fetal environment measures did not attenuate greatly the association between socioeconomic disadvantage and child development outcomes. For example, when adjusting for fetal environment, the risk of abnormal or doubtful development decreased slightly among children whose parents had never worked or were long term unemployed for gross motor skills (Model 1 OR = 1.70; CI = 1.03, 2.80; Model 2 OR = 1.62; CI = 0.97, 2.70), hearing and language (Model 1 OR = 2.14; CI = 1.63, 2.80; Model 2 OR = 1.89; CI = 1.44, 2.48), vision and fine motor skills (Model 1 OR = 3.60; CI = 2.32, 5.58; Model 2 OR = 3.23; CI = 2.07, 5.05), and social development (Model 1 OR = 4.12; CI = 2.46, 6.90; Model 2 OR = 3.72; CI = 2.20, 6.28), and (Table 2). For robustness, we used the Karlson-Holm-Breen (KHB) method to decompose the total effects observed into direct effects (operating purely via the socioeconomic variable) and indirect effects (i.e. via the fetal environment measures, see Table 3). For the majority of parental NS-SEC classes and levels of parental qualifications, the contribution of indirect effects (i.e. via differential fetal environment) were minimal. However for children in households with parents who have never worked or who have no educational qualifications, around a quarter of the effect associated with socioeconomic status appears to be related to the fetal environment measures (based on comparison of indirect effect with total effect, see Table 3).

As part of a wider sensitivity analysis, we also investigated whether there were differentials in the association by the sex of the child (see Additional file 1: Tables S8 and S9). The effect size for socioeconomic position variables for males and females were broadly consistent with the main-effects models estimated in Table 2.

For most children there appears to be no notable socioeconomic pathway through in utero development. However, for children in households in the most socioeconomically challenging situations there is evidence of a small but notable effect. Children growing up in circumstances of socioeconomic disadvantage, manifested through parental occupation and parental education, were more likely to experience abnormal or doubtful vision and fine motor, social, and hearing and language development. Deficits in gross motor skills were not associated with parental occupation but were very slightly more likely among children of parents without educational qualifications or whose highest qualification was O Grade/S Grade. The findings of this study are consistent with Dammann et al. [26] who observed an association between socioeconomic background and intelligence and language skills but not visuomotor development. More recently, Hung et al. identified that children born to socioeconomically disadvantaged parents were more likely to exhibit neurological abnormalities and that this could not be explained by differences in perinatal factors [1]. A meta-analysis of studies investigating gross motor skills and socioeconomic background suggested that findings were inconsistent [27].

The longitudinal dataset created in this study contains information on fetal environment, child development measures, and parental socioeconomic position. MM Black, CR Hess and J Berenson-Howard [28] note that gaps in development by socioeconomic position are typically first observed in toddlerhood. The use of information from a number of reviews from 6 to 8 weeks to 48 months increases the likelihood of correctly measuring development and reduces the problems associated with a single point of observation. A further advantage of using the Scottish Longitudinal Study over other cohort or longitudinal survey datasets is that there is very little loss to follow up. There is also an established history of linking Scottish Morbidity Record (SMR) health data to the SLS. Many previous studies on child development have been based on small sample sizes. Using the SLS is much lower cost and use of secondary data minimises intrusion for data subjects.

The findings of this study suggest that children growing up in circumstances of disadvantage are more likely to have poor development outcomes and this is consistent with other studies [29]. The causal pathways for this relationship are not clear though [30]. It is plausible that socioeconomic disparities in brain structure may explain part of this association [30] and this offers a potential avenue for future study. We cannot identify from the information available within this study where the cause of abnormal or doubtful development was due to genetic conditions or lifestyle factors that pre-date birth (such as alcohol use or use of other drugs which may be detrimental during pregnancy). The developmental measures analysed in this study may be indicative of poor or delayed cognitive skills but also of chronic disabling conditions. N Spencer and L Strazdins [31] and CM Blackburn, NJ Spencer and JM Read [32] have identified an association between socioeconomic disadvantage in early childhood and subsequent development of chronic disabling conditions. What this study may also suggest is that the environment in which children grow up is consequential and that family behaviours differ [33]. Differences in access to resources such as nutrition, access to health care, housing cognitively stimulating materials and experiences and parental expectations and styles have been proposed as possible reasons for the gradient in child development by socioeconomic position [4]. Differential exposure to stress and coping responses to stress are another feasible explanation for the socioeconomic gradient in child development outcomes [4].Without further information on factors occurring in the early years of a child’s life, it is challenging to investigate how these factors moderate, mediate and transact to affect the relationship between socioeconomic position and child development [33].

After adjustment for measures of fetal environment, socioeconomic position was a strong predictor of development of hearing and language, vision and fine motor skills, and social skills but not gross motor skills. For most children this gradient appears to be produced not in utero but either differences in early life environment or possibly a pathway affecting both a mother’s socioeconomic position and her offspring’s development (e.g. genetic/epigenetic). For children of parents with no educational qualification, a poor fetal environment does appear to make a major contribution to the chance of child development abnormalities but the majority of the effect still appears to be through the post-natal environment.

In order to tackle socioeconomic inequalities in child development for most children, a focus on differences in early life environments may be most important. For children in the poorest socioeconomic position interventions should also focus on both early life environment and the health and behaviours of mothers during pregnancy. Future research should examine other factors in early childhood that may influence child development, such as antenatal and postnatal stress [35], to explore whether these mediate the relationship between socioeconomic disadvantage and child development.