Main findings
This systematic review and meta-analyses found that there were no studies before 13 March 2023 that had investigated cognitive scores, cognitive impairment, or low academic performance in early-term births at LGA. Existing studies have analysed the effects of LGA against AGA or early-term births (37 to 38 weeks GA) compared to full-term births (39 to 41 weeks GA) on cognitive outcomes independently, or utilized one of these exposures as a confounder to adjust for this factor in the association with cognitive outcome. Children born at early term were found to have slightly lower cognitive scores, a slightly increased risk for common cognitive impairment, and low academic performance compared to children born at full term. Within the group of early-term born those born at 37 weeks GA tended to have a slightly larger risk than those born at 38 weeks compared to those born full-term. This suggests that there may be a dose-response relationship between GA and cognitive outcome. Compared to AGA children, LGA children had slightly higher cognitive scores, less common cognitive impairment, and fewer had low academic performance in childhood. However, this latter evidence is of low certainty.
According to Cohen’s D of means, a 2-point intelligence quotient (IQ) difference refers to a very small effect size95 (e.g. -0.14 standard difference in means * 15 points = -2.10 IQ difference). When early-term deliveries were examined separately by week of gestation, only a very small clinically significant difference in IQ was found between children born at 37 weeks compared to those born at 40 weeks while no significant difference was found for those born at 38 weeks GA compared to those born full term. Considering that 16-31% of foetuses are born early term, the effect of early term on the overall population IQ may be between 0.4 to 0.7 IQ points maximum, a very small effect. LGA versus AGA birth very slightly favoured those born LGA but the difference was not clinically significant.
There was no study published before 13 March 2023 that considered both gestational age and LGA, i.e. relative birth weight for gestation and its effect on cognitive and academic outcomes. Thus, two possibilities cannot be ruled out, the first being that the small effect of early-term birth may be partly due to confounding by SGA foetuses more often delivered at early term. SGA is a known factor associated with lower cognitive outcomes.96 Accordingly, the small benefit of LGA may be confounded by the gestational age at birth due to the diversity of LGA definitions. The second is that gestational week and weight percentile at birth have additive effects on cognitive development, so that in early-term born LGA babies the two effects may offset each other to some extent.97