In this study of healthy Indian school-age children born in one maternity unit, cognitive scores were higher among ODM’s than controls. Both maternal GDM and higher cognitive performance in the children were associated with higher parental education and/or SES. However, the associations of GDM with better offspring learning, long-term storage/retrieval and verbal ability remained statistically significant after adjusting for these and all other potential confounding factors measured.
Strengths of the study were that we measured a battery of cognitive function tests specifically adapted for, and validated in, a South-Indian population and also collected data on a range of potential covariates/confounders. Limitations in our study were a relatively small number of ODM’s, lack of data on the severity of GDM and treatment, maternal diet and no information on parental intelligence and/or the home environment.
A recent case-control study reported a higher risk of language impairment in ODM’s compared to controls [2
]. A recent review has reported no difference in cognitive ability among children born to mothers with or without GDM; however, compared to controls, ODM’s performed less well in fine and gross motor functions. Further, this review reported inverse associations of offspring intelligence scores, attention, language development, learning, memory-span and mental and psychomotor development with the severity of GDM assessed by glycosylated haemoglobin level and ketonuria, suggesting that offspring cognitive performance could be within normal limits in well-controlled GDM [3
]. The reasons for our finding of higher cognitive function in ODM’s may be that there were no cases of severe or uncontrolled GDM in our study and/or that we were unable to completely adjust for the fact that in our population GDM was associated with higher maternal education, urban residence (and thus better schooling) and better childhood nutritional status (ODM’s had higher BMI). This effect may not be evident in studies in industrialized populations, where GDM tends to be associated with lower SES and lower maternal education [2
]. Alternatively, the fetus of a mother with GDM is exposed to higher concentrations of glucose and fatty acids transferred across the placenta from the maternal circulation [10
]. Theoretically these could enhance brain development. This is perhaps supported by our findings of positive association of maternal 120-minutes glucose concentrations with verbal ability and long-term retrieval/storage among controls; unfortunately we do not have data on maternal circulating fatty acids.
In conclusion, in this population of healthy Indian children, there was no evidence of lower cognitive ability in ODM’s. In fact some cognitive scores (two of the six cognitive parameters tested) were higher in ODM’s. This may be due to residual confounding. Although we adjusted for a number of confounding factors, no SES score can perfectly capture all the effects of SES, especially in India, which has a wide range of SES. Even in the SES matched analysis there were significant differences in other important factors, such as maternal education, age and BMI and child’s birthweight and current BMI, between cases and controls. Alternatively the difference may be due to biological effect. The study suggests for further research to examine the relationship between GDM and offspring cognitive ability in larger studies.