My wife is pregnant with our third child, a boy. I'm concerned about his apparently large head circumference, and how it might relate to a potential developmental disability.
Our older son has PDD NOS or Autistic Spectrum D/O, He presented with a similar body structure as our unborn child. Labor and delivery was long and difficult, and my wife was induced. We suspected our son had problems. He could not suck well from day one, was diagnosed with cranial hypotonia at two years, couldn't sit well at one year, and didn't walked until 28 months.
My wife says our first son's in vitro movements were plentiful, but definitely of low intensity. The last two kids have 'packed a wallop' and are definitely discernible from our oldest.
My unborn son, now at 33 weeks, just had a Level II sonogram. The head was said to be in the 95th percentile, body size was average, but the ratio of the two was also high, but within normal limits. (Note that my wife and her older brother both have somewhat larger heads.)
My question is: can the disproportionate head to body ratio cause muscular problems? Does the difference in in vitro movement mean anything? Can you predict a likelihood of developmental delay given the similar bodily structure of our older son?
Taking the questions in order:
1. No, in general, a disorientate head to body ratio doesn't cause muscular or developmental problems in an otherwise healthy child. The size of our heads is strongly determined by our genes. Big heads run in families, and, alone, don't interfere with development.
2. Does the difference in in vitro movement mean anything? Yes and no. The problem is that fetal movements are very non-specific, affected by the baby's well-being, but also by temperament, positioning, and the experience of the mother. Too many variables mean this sign alone can't be relied on too much.
3. This question seems to be the key one. I asked a neurologist at a large pediatric hospital about the association between a large head and PDD. Apparently, there is a known correlation, at least after birth. But given how strongly correlated family head size is (you mentioned large heads run in your wife's family) it wouldn't be fair to make too much of this correlation.
We have a lot to learn about the PDD/autism spectrum. Depending upon the definition used, between 4 and 21 children out of every 100,000 carry this diagnosis. Boys outnumber girls by 3 to 1, and even more so when the symptoms don't include mental retardation.
We now believe that there must be some genetic component, because having one affected child means there is a 3 percent chance, overall, of having another affected one. (But there is a 97 percent chance of not having one, too.) There are certain inherited syndromes that involve PDD symptoms, though not necessarily a large head to body ratio. At some point, you may want to ask your primary care doctor for a referral to a geneticist or a pediatric neurologist.
Your questions are good and important ones, and those two specialists can best provide you the most updated answers.