WHAAT?  Premature babies are brighter??

When I first saw the findings below I thought I was looking at another example of researchers getting their statistics back to front.  The logical and conventional view is that premature birth harms the baby to some degree.  And that is the official medical view too.  The authors of the study below were obviously pretty perturbed by their results too and turned themselves inside out trying to think of ways in which their very strong study got it wrong. And I think that they went close to isolating the problem, but did not have the psychometric background needed to get it exactly right

The thing that told me what was going on was the Dutch Famine Study.  In the closing phase of WW2, Nederland experienced a severe food shortage.  The mothers of babies born at that time did the best for their infants but a lot still went very hungry.  But a food shortage at that early age could be expected to handicap the infant to some degree, with brain damage being probable.  So when that birth cohort came up for conscription into the Dutch army 18 years later, there was great interest in what their average IQs would be.  Most armies do carry out ability testing as an aid to weeding out soldiers who would be more dangerous to their companions than to the enemy. Putting lethal weapons into the hands of dummies is not recommended.

So what did the Dutch psychologists discover?  Did they find that the average IQ for that year was low?  No. To the contrary, they found that the average IQ was unusually HIGH for that year.

So what had happened?  It was a eugenic effect.  As has repeatedly been shown, high IQ is a marker of general biological fitness -- and only the fit babies survived the famine.  The less fit were weeded out -- died.  So only the fit survived and they had higher IQs than average.

So you might by now see the strong analogy with the results below.  Less fit babies did not survive pre-term birth.  Those who did survive were generally  more fit biologically and hence of higher IQ.  It's actually interesting confirmation of the Dutch findings.  The other finding below, of a slight probability of physical impairment probably shows that even a selection effect cannot cancel out all the stresses and disadvantages that pre-term birth must be expected to impose

Long-term Cognitive and Health Outcomes of School-Aged Children Who Were Born Late-Term vs Full-Term

David N. Figlio et al.


Importance: Late-term gestation (defined as the 41st week of pregnancy) is associated with increased risk of perinatal health complications. It is not known to what extent late-term gestation is associated with long-term cognitive and physical outcomes. Information about long-term outcomes may influence physician and patient decisions regarding optimal pregnancy length.

Objective: To compare the cognitive and physical outcomes of school-aged children who were born full term or late term.

Design, Setting, and Participants:  We analyzed Florida birth certificates from 1994 to 2002 linked to Florida public school records from 1998 to 2013 and found 1?442?590 singleton births with 37 to 41 weeks' gestation in the Florida Bureau of Vital Statistics. Of these, 1?153?716 children (80.0%) were subsequently located in Florida public schools. Linear and logistic regression models were used to assess the association of gestational age with cognitive and physical outcomes at school age. Data analysis took place between April 2013 and January 2016.

Exposures: Late-term (born at 41 weeks) vs full-term (born at 39 or 40 weeks) gestation.

Main Outcomes and Measures:  There were a number of measures used, including the average Florida Comprehensive Assessment Test mathematics and reading scores at ages 8 through 15 years; whether a child was classified as gifted, defined as a student with superior intellectual development and capable of high performance; poor cognitive outcome, defined as a child scoring in the fifth percentile of test takers or having a disability that exempted him or her from taking the Florida Comprehensive Assessment Test; and Exceptional Student Education placement owing to orthopedic, speech, or sensory impairment or being hospitalbound or homebound.

Results:  Of 1 536 482 children born in Florida from singleton births from 1994 to 2002 with complete demographic information, 787 105 (51.2%) were male; 338 894 (22.1%) of mothers were black and 999 684 (65.1%) were married at time of birth, and the mean (SD) age for mothers at time of birth was 27.2 (6.2) years. Late-term infants had 0.7% of an SD (95% CI, 0.001-0.013; P = .02) higher average test scores in elementary and middle school, 2.8% (95% CI, 0.4-5.2; P = .02) higher probability of being gifted, and 3.1% (95% CI, 0.0-6.1; P = .05) reduced probability of poor cognitive outcomes compared with full-term infants. These cognitive benefits appeared strongest for children with disadvantaged family background characteristics. Late-term infants were also 2.1% (95% CI, −0.3 to 4.5; P = .08) more likely to be physically impaired.

Conclusions and Relevance: There appears to be a tradeoff between cognitive and physical outcomes associated with late-term gestation. Children born late-term performed better on 3 measures of school-based cognitive functioning but worse on 1 measure of physical functioning relative to children born full term. Our findings provide longer-run information for expectant parents and physicians who are considering delivery at full term vs late term. These findings are most relevant to uncomplicated, low-risk pregnancies.


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