South Korean nationwide population study finds strong association between low birth weight and subsequent ADHD

Since 1989, South Korea has had a single-payer healthcare insurance system, the Korean National Health Insurance Service. This facilitates nationwide population studies.

A South Korean study team used the national health claims database to retroactively examine the relationship between birth weight and subsequent diagnosis of ADHD for all 2.36 million children born in the country between 2008 and 2012. After excluding children who had since died, who had missing birth weight records, missing income information, or who weighed under400 grams at birth, 2,143,652 children remained in the study cohort.

Gestational age at birth was not available, so could not be taken into consideration.

To reduce the impact of confounding factors, odds ratios were adjusted for sex, history of congenital or perinatal diseases, income, and birth year.

Children with more normal birth weights in the range of 2.5 to 4 kilograms were used as the reference group.

Children with birth weights greater than this reference group were found to be no more likely to develop ADHD than those in the reference group.

At the other end of the spectrum, children with birth weights under a kilogram were 2.2 times more likely to be diagnosed with ADHD than those in the reference group.

That dropped to 1.7 times more likely for those with birth weights from 1 to 1.5 kilograms; 1.5 times more likely in the 1.5-to-2-kilogram range, and 1.4 times more likely in the 2-to-2.5-kilogram range. This dose-response curve, accelerating steeply with lower birth weights, points to a strong association.

For autism spectrum disorder (ASD), the association was even stronger. Again, there was no significant association with higher-than-normal birth weight. But children in the 2-to-2.5-kilogram range were 1.9 times as likely to be diagnosed with ASD; those in the 1.5-to-2 kilogram tranche over three times as likely; those in the 1 to 1.5-kilogram tranche five and halftime as likely, and those under 1 kilogram over ten times as likely.

The authors concluded, “In this national cohort, infants with birth weights of < 2.5 kg were associated with ADHD and ASD, regardless of perinatal history. Children born with LBW [low birth weight] need detailed clinical follow-up.”

In Gyu Song, Han-Suk Kim, Yoon-Minho, You-na Lim, Duk-Soo Moon, Seung Han Shin, Ee-Kyung Kim, Joonsik Park, Jeong Eun Shin, Jungho Han, and Ho SeonEun, “Association between birth weight and neurodevelopmental disorders assessed using the Korean National HealthInsurance Service claims data,” Scientific Reports (2022)12:2080, published online,