Birthweight and Academic Achievement Through Adolescence

Studies of birthweight and academic achievement have focused on low or very low birthweight thresholds or continuous birthweight and early childhood academic outcomes. This study examines the relationship between birthweight and children's academic achievement across the entire birthweight distribution and throughout childhood and adolescence.

Birth certificates for children born in Iowa from 1989 to 2010 are linked to standardized school math and reading tests through 2017 to 2018. Birthweight is examined in 100-g ranges. Outcomes are math and reading scores over grades 2 through 11. Differences in achievement by birthweight are estimated in a regression controlling for child, maternal, and school/testing covariates, pooling grades and separately for elementary, middle, and high school.

The sample is nearly 75% of the birth population and includes over 592,000 unique children and 3.9 million child-grade observations. Academic achievement generally improves with higher birthweight but in smaller increments. Gaps in standard deviations (SDs) of math (reading) scores are 0.55 to 0.75 (0.28-0.53) SDs at 501 to 1000 g, 0.34 to 0.44 (0.18-0.29) SDs at 1001 to 1800 g, and 0.15 to 0.27 (0.11-0.19) SDs at 1801 to 2700 g compared to the median/mean birthweight range of 3401 to 3500 g. Math gaps at lower birthweights are overall larger than reading. Gaps are persistent over school years but appear to narrow by high school.

There are meaningful academic achievement gaps below median/mean birthweight that persist throughout childhood and adolescence. It is important to consider detailed birthweight data rather than pre-established thresholds for informing medical and learning interventions and to bolster these interventions to address developmental and learning gaps.