Birth weight and IQ

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Aftenposten, one of the leading newspapers in Norway, ran a story on Saturday about a study on birth weight and IQ conducted by Martha Gunn Eide, a researcher at the University of Bergen. (Eide is a medical doctor and this research represents her work toward a Doctorate of Medicine degree. Her thesis is entitled “Associations of Perinatal Conditions with Adult Body Size and Intelligence: A Register-based Cohort Study in Norway 1967-1999.”)

Below the fold are some highlights from the article (apologies for the rough quality of my translation!) >>

“Store babyer faar hoeyest IQ” ["Big babies get highest IQ"]

The birth weight of a newborn baby boy has significance for intelligence, course [success] and income….

[Martha Gunn] Eide defends in a few days her Dr. Med. degree at the University of Bergen. She has completed a very comprehensive study based on the combined data of nearly 400,000 male children.

“Are there grounds to believe there is a correlation between birth weight and IQ also in girls?”

“There is no call to believe that this would be appreciably different for girls,” says Eide, who is affiliated with The Department of Public Health and Primary Health Care, Faculty of Medicine at the University of Bergen.

Her study is based on information from the Medical Birth Register, Vernepliktsverket [compulsory military service department], the Statistics Central Bureau and the Rikstrygdeverket [Social Insurance department]. With this Eide has followed ca. 317,000 baby boys that were born in Norway between 1967-1979 through 18 years, as they met the [military] recruitment in period 1984-1999.

“The data are comprehensive facts analyzed for all boys in Norway over a 13 year period,” says the Bergen researcher, who has worked four years on the project.

5200 gram

“What we find is that birth weight is important for IQ. Higher birth weight, higher IQ,” says Kjell G. Salvanes [1], professor in Social Economics at the Norwegian School of Economics and Business Administration in Bergen….

Professor Salvanes has, together with two other international researchers, Sandra E. Black in Los Angeles and Paul J. Devereux in Dublin, investigated which factors are responsible for who takes higher degrees and get jobs with the highest pay….

godless discussed birth weight and IQ here while musing on C-sections as artificial selection.

[1] From the Cradle to the Labor Market? The Effect of Birth Weight on Adult Outcomes – Sandra E. Black, Paul J. Devereux, Kjell Salvanes

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16 Comments

  1. cannot get much info there re details of the study. 
     
    to makle sense the study would necessarily have to have excluded from analysis infants w b wts < 1500 and preferably < 2500 gms. as we alrerady know that low bwt infants can have cognitive impairmrnt at rates higher than normal. it would also need to exclude infants with intrauterine growth retardation, and infants of diabetic mothers . just some prelim stuff i can think of offhand. 
     
    would love to see a translated link that has reference to materials and methods!

  2. “data of nearly 400,000 male children.” 
     
    this makes me think that the study was done using some form of a nationalized birth registry etc.  
     
    while birth registry data from Norway is rather good most times, if you do not exclude preterm infants etc. You will get a large skew from these outliers. Also, if you do not exclude preterm infants it is rather ho hum as everyone has known this for decades. 
     
    now if the study looks at kids who were between 2500-4000gm b wt and comes to the same conclusion that would be very interesting. And be a good strting point for further hypothesis generation.

  3. would love to see a translated link that has reference to materials and methods 
     
    Yes — I did try looking around for more detailed info but without any luck. 
     
    She defended her dissertation today (Mon), so perhaps her thesis and/or other publications by her will become available in the near future.

  4. Womb Needed For Proper Brain Development 
     
    http://www.sciencedaily.com/releases/2005/11/051122205607.htm 
     
    ?These findings indicate that the normal early maturation of the brain may be compromised when it takes place outside of the womb,? said Witelson. ?We found that in very premature babies, a part of the brain doesn?t show normal growth after birth, and in fact some parts of the brain didn?t change at all from the day the babies were born until they reached what would have been a full-term birth date.? 
     
    The length of time in the womb may be more important than birth weight. Perhaps 10-month babies average higher IQ even after adjusting for birth weight. Or perhaps both size and gestation period are important.

  5. Well, if anyone’s really interested, her thesis can apparently be purchased by contacting Eide directly >> 
     
    For kjøp/bestilling av avhandlingen kontakt kandidaten direkte. 
     
    Her details are here >> 
     
    http://www.uib.no/info/dr_grad/2005/EideMartha.htm 
     
    It’s not clear to me whether the thesis is in English or Norwegian — the title is given in English on the university’s page about her. ??

  6. Fly: 
     
    “10-month babies” may have a higher iq but it would manifest in baby heaven. 
     
    in a singleton prgnancy, if we graph mortality rates vs gestation. Mortality keeps decreasing till you get to 38-40 weeks ( 9 months) after that there is a vey sharp uptick. Most likely consequent to increasing uteroplacental insufficiency. Most 10 month infants would either be dead or severely neurocompromised.

  7. Fly: 
     
    ?These findings indicate that the normal early maturation of the brain may be compromised when it takes place outside of the womb,? said Witelson. ?We found that in very premature babies, a part of the brain doesn?t show normal growth after birth, and in fact some parts of the brain didn?t change at all from the day the babies were born until they reached what would have been a full-term birth date.” 
     
    The process of neuronal migration and then the neurons establishing synaptic links with each other is controlled by both the ” program” and the programs interaction with the environment and feedback. Believe me the Neonatal ICU environment is very different from the inside of a womb. 
     
    While I do not know specifically about the particular findings that the study cited is talking about, we do see on an ongoing basis, some small degree of ventricular dilatation in recovering prematures. The obvious assumption, which most of do not want to talk about is that this represents mild hydrocephalus ex vacuuo. ie the ventricles filling out a little to accomodate loss of brain tissue.

  8. Vic: ?Mortality keeps decreasing till you get to 38-40 weeks ( 9 months) after that there is a vey sharp uptick. Most likely consequent to increasing uteroplacental insufficiency. Most 10 month infants would either be dead or severely neurocompromised.? 
     
    Interesting. I was a 10-month baby. My mother feared that I was retarded because I didn?t speak until around age 4. At that age I began speaking in complete sentences. 
     
    I assume that in the US today birth would be artificially induced before 10 months.

  9. absolutely 
    no chance leaving it to chance 
    you would have a c section before 43 weeks and there is a trend to go in even by 41 weeks

  10. Fly, 
     
    My daughter’s mother was induced at 10-months, and my daughter was a c-section birth at almost 10-months. She was a large baby, was born eyes open, and has always been advanced for her age. At 2.5 yo she can count to 20, knows the alphabet and can spell her name and recognize it and a few other simple words. I hope she’ll be reading by 3 or 4 yo. 
     
    Interestingly her mother and I were both the heaviest at birth and highest IQ’ed of our respective siblings.

  11. I believe a study (by Ian Deary and collegues?) that came out within the last year or so showed that IQ is correlated with birth weight even within the normal range of birth weights. I might comment again if I find the PDF on my regular computer. 
     
    I wonder if the relationship is mediated by head weight. As babies are disproportionately big headed, it might be that heavier babies tend to have higher IQs later because their heads are heavier.

  12. Intelligence  
    Article in Press, Corrected Proof 
     
    Low birthweight and social disadvantage: Tracking their relationship with children’s IQ during the period of school attendance  
     
    Naomi Breslau, William T. Dickens, James R. Flynn, Edward L. Peterson and Victoria C. Lucia 
     
    Abstract: 
    Generalized estimating equations were used to examine the relation of low birthweight, an indicator of adverse perinatal events, and social disadvantage to IQ changes during the period of school attendance. Data are from a longitudinal study of low birthweight and normal birthweight children in two disparate communities, an inner-city and near-by suburbs in southeast Michigan (n = 773). Wechsler intelligence tests were administered at ages 6, 11 and 17. Low birthweight-related deficits (vs. normal birthweight) detected at the start of schooling were about 5 IQ points and these remained constant up to age 17. Initial IQ deficits associated with urban environment (vs. suburban) increased significantly from age 6 to 11, but no further by age 17. These trends were independent of one another: The low birthweight deficit was constant across social environments; the social disadvantage deficit was uniform across birthweight groups. The finding that the urban?suburban gap did not continue to widen after age 11 probably resulted from an atypical IQ decline of suburban children. The causes of this unexpected finding are unclear. 
     
    http://dx.doi.org/10.1016/j.intell.2005.10.003

  13. source* 
    http://tinyurl.com/8suk7 
     
    This contradicts other data I have seen that suggests that IQ increases up to a certain point and then goes down. So that a 6 and 10 pound baby would both be expected to have the same IQ. The book has a graph of the data that didnt on the page after the one I linked to. 
     
    * There did not appear to be a way to cut a small part of the text.

  14. This finding seems consistent with Rushton theory.

  15. Related interest: Bigger brain size matters for intellectual ability 
     
    http://www.eurekalert.org/pub_releases/2005-12/mu-bbs122205.php

  16. I’m not a scientist, so I’m lost at sea here, but thought I’d throw myself in as an outlier. 
     
    I was born at 14-weeks in a hospital in New York in 1963; weight was 3.4 pounds. Spent the year after in an incubator, surviving pneumonia and two hernia operations. Up until age 14-15, had serious but infrequent “dizzy spells” — which was alays explained as an inner ear imbalance owing to slow development. Otherwise healthy. 
     
    Unfortunately no idea about IQ, though I did graduate from college normally, later got MA and PhD, so can’t have too low an IQ, yes? (well, ok, maybe not…) 
     
    I guess I’d be critical of a study that claimed a direct connection between low birth weight and IQ/later success in life. Isn’t the lesson of all these types of studies that it is parental care and other quality of life variables that trump all?

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