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