Interpretation
There is a paucity of existing studies that stratify children born at the same gestational week according to their birth weight percentile (or vice versa). Several systematic reviews6-10, 20 that evaluated the relationship between early-term delivery and cognitive or academic outcomes are consistent with the conclusions of our review. In terms of foetal growth, although there is a systematic review and meta-analysis with good quality showing that SGA is detrimental to cognitive development,96 we found no extant systematic reviews synthesizing evidence on cognitive development or academic performance in children with LGA. Analysis by gestational age or LGA separately is unable to answer whether these effects are additive to or moderate each other.
Firstly, observational studies are required that allow the investigation of the effect of LGA or relative birthweight at each gestational week on cognitive and academic outcomes. A new study published after March 2023 utilized four cohort studies (N: 30 643)97 and reported that relative birthweight (birth weight percentile per gestation) and gestational week are two exposure factors that independently affect cognitive scores in childhood and are thus additive. IQ linearly increased by 4.2 points as birth weight centiles increased from the 1st to the 69th percentile before completely plateauing (i.e. no more IQ gain at larger birth weight). Above 32 weeks gestation, each GA week gained was associated with a 0.3 IQ increase similar to previous study reports.98Future studies are needed to report relative birthweight per gestational week and its effect on cognitive outcomes for obstetric decision-making.
Secondly, the most desirable would be to have a randomized clinical trial comparing the effect of early-term induction for LGA versus expectant delivery on shoulder dystocia with long-term follow-up of cognitive and academic outcomes on the of the child. Considering the suggested small effect sizes, this will require large participant numbers.