IQ and Birthweight Linked in Normal Birthweight Children, Too

Join Our Community of Science Lovers!

In recent years, a number of studies have shown that low birthweight babies have lower IQ test scores at school age. Now findings reported in the current issue of the British Medical Journal indicate that a link between size at birth and IQ also exists in normal birthweight children. According to the study, bigger babies go on to receive higher scores on childhood intelligence tests.

Thomas Matte of the New York Academy of Medicine and his colleagues probed the relationship between birthweight and measured intelligence at age seven in more than 3,000 children, most of who had normal birthweights. Even after accounting for maternal age, race, education, socioeconomic status and birth order, the team found a direct association between the two.

The relationship was especially pronounced in boys. For example, whereas a one-kilogram increase in birthweight was linked to a 4.6 increase in IQ score in boys, the same birthweight increase in girls related to only a 2.8 increase.


On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.


"Considerable efforts continue to be directed at understanding causes of low birthweight, its neurodevelopmental consequences, and the mechanisms linking the two," the authors write. "Evidence from this and other studies suggests that these efforts should be broadened to examine the influences on fetal growth among those with normal birthweight and the neurodevelopmental consequences of such variation."

Kate Wong is an award-winning science writer and senior editor for features at Scientific American, where she has focused on evolution, ecology, anthropology, archaeology, paleontology and animal behavior. She is fascinated by human origins, which she has covered for nearly 30 years. Recently she has become obsessed with birds. Her reporting has taken her to caves in France and Croatia that Neandertals once called home to the shores of Kenya’s Lake Turkana in search of the oldest stone tools in the world, as well as to Madagascar on an expedition to unearth ancient mammals and dinosaurs, the icy waters of Antarctica, where humpback whales feast on krill, and a “Big Day” race around the state of Connecticut to find as many bird species as possible in 24 hours. Wong is co-author, with Donald Johanson, of Lucy’s Legacy: The Quest for Human Origins. She holds a bachelor of science degree in biological anthropology and zoology from the University of Michigan. Follow her on Bluesky @katewong.bsky.social

More by Kate Wong

It’s Time to Stand Up for Science

If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.

I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.

If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.

In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.

There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.

Thank you,

David M. Ewalt, Editor in Chief, Scientific American

Subscribe