A thesis submitted to the Faculty of Health Sciences,
University of the Witwatersrand
in fulfilment of the requirements for the degree of Doctor of Philosophy
Johannesburg, South Africa
2017.Background
Exposure to biological and psychosocial risks, particularly during the first three years
of life, affects brain development and compromises the short- and long-term health
and development of children, as well as their educational achievement and long-term
productivity. This study sought to determine the effects of maternal and child
environmental and psychosocial exposures during pregnancy and the first two years
of the child’s life on growth and development outcomes in early childhood (up to 5
years) in an urban South African birth cohort.
Methods
Data used for this study was from the Birth to Twenty Plus (Bt20+) longitudinal birth
cohort study, initiated in 1990 in the greater Johannesburg metropolitan area, South
Africa. First, the associations between exposure to nine maternal risks, assessed in
1228 women, and subsequent infant birth weight was assessed. Second, the study
examined the effects of risk exposure to the mother (and child) during pregnancy and
the first year of a child’s life on stunting at age 2 years in 1098 mother–child pairs.
Finally, the associations between ten demographic and psychosocial exposures
occurring during the third trimester of pregnancy and the first two years of a child’s
life and child development age 5 were examined in 636 mother-child pairs.
Multivariable regression analyses were used to investigate associations between
exposures and outcomes. Further analysis was undertaken to assess whether early
life growth mediated the associations between maternal and household exposures
and child development outcome at age 5.
Results
Unwanted pregnancy (or ambivalence) was associated with a ~156 g reduction in
infant birth weight (β = −0.32, 95% confidence interval (CI): −0.51, −0.14). Tobacco
use during pregnancy was negatively associated with BWZ (β = −0.32, 95% CI:
−0.59, −0.05). Exposure to both these risks was associated with cumulative
reductions in birth weight.
Approximately 1 in 5 children were stunted at age 2 years, with males at greater risk
than females. Higher maternal education was protective for females (adjusted odds
ratio (AOR) = 0.35; 95% CI: 0.14, 0.87), while higher household SES was protective
for males (AOR for richest SES group = 0.39; 95% CI: 0.16, 0.92).
Males scored significantly lower than females on the developmental measure at age
5. Improved child developmental outcome was associated with higher birthweight for
both sexes and superior linear growth in males. R-DPDQ scores increased by 0.84
units for every 1 SD increase in relative linear growth between birth and two years (β
= 0.84 [95% CI 0.30, 1.39]). Socio-economic status (for both sexes) and maternal
education for males were significant predictors of better child development. Growth
status did not mediate the effects of socio-economic status (either sex) or maternal
education (males) on developmental outcome.
Conclusion
Social factors, especially social determinants such as household SES and maternal
education, were associated with early childhood growth and development in this
context. Prenatal (using birthweight as a proxy) and postnatal growth were important
for child development. Males were particularly vulnerable to poor growth and
development in this cohort. The effects of household SES and maternal education on
child development at 5 years were not mediated by linear growth between birth and 4
years.LG201
