Brainy?

Peter had a physical with his pediatrician on Monday.  Dr. Selim commented that Peter had a good year – very few infections or health issues, especially when you consider the rough start he had.  I have to agree.  Peter continues to hit his milestones in accord with his adjusted age, and it’s looking like he won’t need surgery to repair his hydrocele.  However, his measurements still betray the fact that he was a preemie:

Weight = 18 lbs, 12 oz = 2 percentile

Height = 27 in = 0.1 percentile

Head circumference = 48.3 cm = 89 percentile

The percentiles I listed above are based on his actual age; if you compare him to babies born on his due date, he is 11 percentile for weight, 4 percentile for height, and 97 percentile for head circumference.  That makes the height and weight measurements look better, but I’m still left wondering where Peter got his big noggin.

Although Peter is undeniably adorable, he does look quite disproportionate when I compare him to the other babies in his playgroup.  He is as tall as the 7-month-olds, but his head is as big as that of a 20-month-old.  Peter’s head circumference tracked 50 percentile for his adjusted age as a newborn, and I used to be able to guess how old other babies were based on the size of their heads.  However, in the past 6 months or so, Peter’s head circumference has shot up by 2 standard deviations on the growth chart, and I’ve lost my sense of scale with regard to baby head sizes.

I’m glad that Peter’s pediatrician ordered a cranial ultrasound after his last check-up.  If I had not already been reassured that Peter does not have hydrocephalus, I would probably be worrying rather than marveling right now.

I recently read that babies with big noggins tend to be late walkers.  They have higher centers of gravity, so it is more difficult for them to balance.  So far, Peter is able to stand unassisted for 5 seconds or slightly longer, but I don’t think he’s going to start walking for at least another month.  He needs time to improve his balance.  I can be patient; Peter’s bear crawl is quite endearing.

Peter’s pediatrician mentioned that in his experience, children with big heads tend to be bright.  I thought he was just pulling my leg, but then I found this article.

For me, the take-home message was that I should be glad that Peter’s head grew so dramatically in his first year of life.  Barring hydrocephalus or other neurological issues, head circumference in infants and children correlates quite well to brain volume.  Older studies have shown that for very low birth weight infants, good head growth during the first year of life correlates to intelligence later in life.  This particular study looked at full-term infants, but it also showed that the head growth during infancy is a significant predictor of IQ at 8 years of age.  Head growth between ages 1 and 4  and between ages 4 and 8, on the other hand, was not correlated with IQ at age 8.

Since Peter moved 2 standard deviations up the growth chart for head circumference during his first year of life, his full-scale IQ at age 8 should be a whopping 3.12 points higher than some hypothetical other child with a medical history similar to that of Peter and whose mother treated him exactly the same way that I treat Peter but who tracked 50 percentile for head circumference throughout infancy.

If you’re thinking that other environmental and genetic factors are likely to have a much greater influence on Peter’s IQ at age 8 than his head growth as a baby, I’d have to agree with you.  It’s unlikely that Peter will be the next Isaac Newton (did I ever mention that Newton was a preemie?), but I’m happy that his head is growing well, nonetheless.

And no, Peter is not standing unassisted in this photo.  He is cheating by leaning against the refrigerator.

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