Wednesday 30 July 2014

Morning sickness and child intelligence


Morning sickness may mean healthier, intelligent baby opined the headline, and although no link was given, the journal and lead author were mentioned, which lead me to a brand new meta-analysis of the effects of treated and untreated morning sickness on child development. Within that analysis there is one 2009 paper by Nulman which included intelligence testing. So, the “news” is five years old, but interesting nonetheless.

Long-term Neurodevelopment of Children Exposed to Maternal Nausea
and Vomiting of Pregnancy and Diclectin. Irena Nulman, MD, Joanne Rovet, PhD, Maru Barrera, PhD, Dafna Knittel-Keren, MA, Brian M. Feldman, MD,
and Gideon Koren, MD. (J Pediatr 2009;155:45-50).

In a study comparing long term development of children whose mothers suffered from NVP to children born to women not experiencing NVP, Nulman et al. recruited 3 groups of children: 45 born to mothers with NVP treated with doxylamine–pyridoxine, 47 born to mothers with untreated NVP, and 29 born to mothers with no NVP. Children aged 3–7 years received a comprehensive set of psychological tests including measures of intelligence, neurocognitive abilities and behavior. Mothers were assessed for IQ, socioeconomic status and educational level and severity of their NVP symptoms. Although all children scored in the normal range for IQ, those who were exposed to NVP scored higher than the non-exposed group on performance IQ (P < 0.02), NEPSY verbal fluency (P < 0.003), phonological processing (P < 0.004), and McCarthy numerical memory (P < 0.004). Regression analysis adjusted for child’s sex and age identified the predictors of enhanced results to be NVP severity and maternal IQ.

Children’s intelligence was evaluated with the Wechsler Preschool and Primary Scale of Intelligence–Revised (WPPSI-R) or the Wechsler Preschool and Primary Scale
of Intelligence, Third Edition (WPPSI-III) which provided an index of Verbal IQ (VIQ), Performance IQ (PIQ), and Full-Scale IQ (FSIQ). Children also underwent: 6 NEPSY subtests (Visual Attention, Verbal Fluency, Comprehension of Instructions, Visuomotor Precision, Sentence Repetition, Narrative Memory); the Preschool Language Scale (PLS-III or PLS-IV); the Beery Developmental Test of Visual-Motor
Integration (VMI); Wide Range Assessment of Visual Motor Abilities (WRAVMA) Pegboard and Matching subtests, and 3 memory subtests of McCarthy Scales of Children’s Abilities (Pictorial Memory and Forward and Backward Numerical
Memory). All tests administered were applicable to the range of ages in the study cohort. In addition, mothers completed the Child Behavior Checklist (CBCL) and Conner’s Parent Rating Scale questionnaires to assess child behavior and attention problems for children aged 3 to 17 years. The physician also assessed children’s general health, weight, height, and head circumference. Maternal FSIQ was determined with the Vocabulary and Matrix Reasoning subtests of Wechsler Abbreviated Scale of Intelligence (WASI). SES was measured with the Hollingshead Four Factor Index, which provides a 5-point social class ranking (1 = high, 5 = low) on the basis of parents’ education and employment.

The key findings are in Table II.

                              NVP+diclectin(45)  NVP no diclectin(47)  No NVP(29)

Mother’s tests
WASI Full Scale IQ  107.5 sd 8.8           108.9 sd 11.7          106.3 sd 11.6     NS

Children’s scores

WPPSI Verbal IQ     112.2 sd 13.4          112.9 sd 13.57        110.3 sd 17.9      NS
Performance IQ       120.9 sd 13.9          112.6 sd 13.1           114.9 sd 14.2   P .010
Full Scale IQ             118.7 sd 13.4          114.6 sd 12.8           112.0 sd 15.5     NS

Comment: The mothers are slightly above average, the children apparently very much above average. Either the fathers are all extremely bright or the tests for the children are over-estimates, perhaps a standardisation issue. It would appear that Performance IQ is about 4 to 6 points higher in mothers who were treated for morning sickness, though this is not statistically significant in these small samples. There were significant differences in fluency, phonological processing, and pictorial and numerical memory.

NEPSY Verbal Fluency   11.85 sd 2.57      11.55 sd 2.50         9.93 sd 3.06   P = .013
Phonological Processing 11.02 sd 2.81       10.75 sd 3.31        9.07 sd 3.44   P = .033
McCarthy Pictorial Mem 12.43 sd 2.97      10.37 sd .32        10.62 sd 3.21   P = .017
Numerical Mem               11.68 sd 2.21       11.39 sd 2.30       9.77 sd 2.32   P = .018

If you close your eyes, forget about treatment, and just compare the results for those mothers who had nausea and vomiting against those who did not, the results look more clear cut, with a 7 point Performance IQ difference:

Test Scale/subtest                              NVP (n 92)                 No NVP (n29)    P value
WPPSI Performance IQ                  116.7 sd 14.1                109.6 sd 13.4       .02
NEPSY Verbal Fluency 1                     1.7 sd 2.5                     9.9 sd 3.1          .003
NEPSY Phonological Processing        10.9 sd 3.0                   9.1 sd 3.4          .004
McCarthy Numerical Mem Forwds    11.5 sd 2.2                   9.8 sd 2.3           .004

There is something here to warrant further investigation, even though the samples are small and there is some cherry-picking of significant results. It would certainly be good to follow up these children and test them now that they are older, because the measures of general intelligence will now be better predictors of the levels they will attain in adulthood.

Morning sickness, the authors speculate, may indicate that the child is receiving a better hormonal environment, boosting their system integrity at the cost of the mother having more physiological demands being made of her, and consequently feeling ill. It constitutes an interesting leading indicator of intelligence.

Incidentally, if anyone wants to replicate Dan Freedman’s baby studies on newborns, or Simon Baron-Cohen’s attentional studies on newborns, then if any of this stuff is true then within 30 hours of birth we should be able to pick up some predictors of later intelligence. Worth a look.

Finally, this being a monarchy, the newspaper story was illustrated with a Royal baby. This reminds me of a remark made to me some years ago: if intelligence depended upon the richness of the environment provided to babies, the Royal Family should be the brightest people in the world. Which they may be, your Royal Highness.


  1. Why did the mothers treated with doxylamine–pyridoxine have the highest IQs? Was this an artifact of the small sample size?

  2. I think it is because the anti-emetics helped the mothers stay healthy, and not get malnourished or dehydrated.

    Nausea and vomiting of pregnancy (NVP) is a poorly understood phenomenon seen in as much as 80% of pregnancies,
    with symptoms peaking between 5 and 12 weeks gestation.1 Although self-limited, NVP may have an unfavorable impact on women’s health. Approximately one-half to two percent of pregnant women experience the most severe form of NVP, hyperemesis gravidarum (HG),2 which is defined as persistent vomiting not related to other causes that may interfere with nutrition and fluid intake. HG is associated with ketonuria, electrolyte imbalance, dehydration, and weight loss. It is
    additionally associated with childhood behavioral difficulties in offspring.
    HG, the most common reason for hospitalization in the first trimester of pregnancy, may be prevented with timely treatment with anti-emetic drugs. In Canada, the only approved anti-emetic drug for use in pregnancy is diclectin, which contains 10 mg
    each of doxylamine and vitamin B6 in a delayed-release formulary. Separately, these components are used worldwide to control NVP.
    It has been postulated that NVP, which is a byproduct of altered secretion of hormones (namely human chorionic gonadotropin and thyroxine) to ensure adequate placental growth, is a marker for fetal protection deemed the ‘‘Maternal and Embryo Protection Hypothesis.’’ NVP is associated with favorable fetal outcomes, including reduced rates of miscarriage, stillbirth, preterm birth, intrauterine growth retardation, and congenital malformations.

  3. The size of the differences in IQ are much smaller than the standard deviation - which (to my mind) means the differences are not robust, and - even if true - are not usefully predictive at the individual level.

    The doxylamine antihistamine is a sedative, which would tend to reduce performance in an IQ test - except among people with high anxiety levels when it might increase performance - although this may be compensated (to some extent) by an empathic IQ tester allowing more time etc. I suppose there should have been a normal control group given the antihistamine, to tease out its effect on the IQ test.

    Twenty years ago Margie Profet's evolutionary explanation of pregnancy sickness was one of the things that got me into evolutionary psychology

    Having said all this - I would be surprised if pregnancy sickness did not correlate in some way with IQ, because pretty much everything else does, one way or the other.

    I am surprised, or not really, by the lack of research on the disadvantages of high IQ/ advantages of low IQ -

    but the reason is probably that some disadvantages (such as low fertility) are regarded (by high IQ people) as advantages - while some advantages (such as the kind of athleticism advantageous in agonistic conflict) are only apparent between races, not within.

    1. Thanks. Will read the links. The 7 point difference in Performance IQ is almost half a standard deviation, which I see as a sizeable effect. There is certainly a folk wisdom view that high IQ is a baleful gift, despite all the obvious and well supported advantages.

  4. Thank you for the response. My wife has had NVP with all seven of her pregnancies. There are quite a few claims that mineral deficiencies (e.g. magnesium) are the cause but I haven’t seen any definitive studies.

  5. I think we should note that NVP is said to be pretty usual, as high as 80% in some accounts!

    1. It’s interesting that the severity varies from woman to woman, and even from pregnancy to pregnancy for a particular woman. I wonder if severity correlates with childhood IQ.

      NVP is a very depressing thing for a woman to go through and I think the knowledge that it’s an indicator of smart and healthy children could help women to get through it.

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