Skip to main content
Baby Corner logo
Login | Sign Up

Heavier Birth Weight Equals Higher IQ

Katrina Wharton |19, October 2014


A paper out of Northwestern University's Institute for Policy Research looked at the effect of weight at birth and later cognitive abilities. The researchers used birth and school records for all children born from 1992 to 2002 born in Florida to discover the effect of birth weight on IQ.

The researchers found that the cognitive effects of birth weight remained constant through schooling, when factoring for family backgrounds and other variants such as school quality. According to the research, poor neonatal outcomes on adult health are set early.

This certainly isn't the first study to find a link between heavier babies and better intellectual outcomes. A 2001 study, published in the British Journal of Medicine, and conducted by Britain's Medical Research Council, found that birth weight influenced IQ, at least until age 26 when the results evened out.

The researchers looked at 3900 British men and women born in the year 1946 who were followed from birth and had IQ tests administered at age 8, 11, 15, 26 and 43. The study only included babies who weighed over 5 pounds, 5 ounces at birth, which is considered normal birth weight. From those over normal weight, those on the heavier side had higher IQ results. Researchers found that the most reliable indicator of intelligence was the test result at age 8.

The researchers found the data to be consistent regardless of gender, birth order, mother's age or education or father's social class. However, lead researcher, Marcus Richards, a psychologist, warns parents of smaller babies not to despair.

"Birth weight is only one of numerous factors that influence cognitive function. It may not actually be a very powerful one."

He states that parental involvement in a child's education, from attending PTA meetings to overseeing a child's homework can be huge factors.

In 2013, a study out of the University of Adelaide, showed that increased head circumference and weight gain in the first month of life was linked to higher IQ in early school years.

The study, conducted by Adelaide Public Health, and published in the journal, Pediatrics, looked at data from 13,800 children born at full term. The study's results showed that children who weighed 40 percent more than their birth weight during the first month had achieved an IQ of 1.5 more points at the age of 6 than babies who gained 15 percent of their birth weight. Babies who had the largest head circumference measurements tested with higher IQ levels.

Dr. Lisa Smithers, lead author of the study, said, "Head circumference is an indicator of brain volume, so a greater increase in head circumference in a newborn baby suggests more rapid brain growth."

She further explained the IQ results, "Those children who gained the most weight scored especially high on verbal IQ at age 6. This may be because the neural structures for verbal IQ develop earlier in life, which means the rapid weight gain during that neonatal period could be having a direct cognitive benefit for the child."

The researchers were aware of previous studies looking at early diet after birth and IQ, however, this was the first study that looked specifically at the baby weight gains in the initial month after birth.

Dr. Smithers sees encouragement of newly breastfeeding mothers as a priority in light of the study results. "We know that many mothers have difficulty establishing breastfeeding in the first weeks of their baby's life," she said.

While it cannot be advised how to develop heavier babies, most researchers tend to agree that the heaviest babies are generally produced by healthy and well-built mothers. This isn't a reason to overeat, however, as babies born to mothers who are too heavy face negative results.

The researchers included David Figlio, Professor at Northwestern University; Johnathan Guryan, Associate Professor at Northwestern University, Krzysztof Karbownik, a visiting Scholar at Northwestern University; and Jeffrey Roth, Research Professor of Pediatrics at University of Florida.

Related Articles

Baby Weight Gain During the First Year

Can Babies Swim at Birth?

New Study Shows Infants Learn Language Before Birth

Speech Development in the First Year

The Importance of Touch to Your Baby


Showing 1 - 2 out of 2 Comments
Add Comment or question.

Clivy Jan 28, 2017 09:10:50 PM ET

I weighed about 7.6 lbs at birth, but would not consider myself smart. Though I do have the highest science grades in my class, and I was one of only 2-3 students who actually got an A on their science notes.

Reply | Report

cwhite910 Oct 30, 2014 05:59:47 PM ET

I guess my son will be smart than. He was born 8.4 lbs.

Reply | Report

Add Comment

You are commenting as .

Baby Photo Contest - WIN!
Enter your baby into Baby Corner's free baby photo contest for a chance to win prizes!

Vote Today
Upload & Manage Your Photos

August 2019 Baby Photo Contest Winner
August 2019 Baby Photo Contest Winner
Congratulations Mishapauli14!!

Your Baby Month by Month
Learn what to expect during your baby's first years with our month by month baby calendar. Choose your baby's age below to see how your baby is developing.

1 Week
2 Weeks
3 Weeks
4 Weeks
2 Months
3 Months
4 Months
5 Months
6 Months
7 Months
8 Months
9 Months
10 Months
11 Months
12 Months
13 Months
14 Months
15 Months
16 Months
17 Months
18 Months
19 Months
20 Months
21 Months
22 Months
23 Months
24 Months

New Today at Baby Corner