Cindi wrote us about her child being born left-handed when there isn’t an obvious hereditary link and said she'd found a few articles linking left-handedness to prenatal ultrasounds. So I gathered up my notes on this topic to share with you.
Sinistrality or being sinistral means "left-handed," oriented toward the left, or going counter-clockwise.There you have a new "word for the day."
8-15 % percent of the population is left-handed as a result of heredity. One of my sisters is a “lefty,” and my housemate tells me many of his relatives (born before the introduction of prenatal ultrasound) are left-handed—by heredity. However, in recent decades there has been a puzzling rise in left-handedness. When the rate of left-handedness rises above 9 % in offspring born to right-handed parents and above 35% for children of left-handed parents--something other than heredity is impacting the unborn. Doctors have known for a long-time that when left-handedness is not genetically-determined, it can be a sign of brain damage. Prenatal ultrasound has been suggested as the common factor, or “insult,” causing the new rise in left-handedness.(1)
An increase in non-right-handedness (left-handed or ambidextrous) has been associated with ultrasound exposure from early studies (Salvesen, Bakketeig et al. 1992; Salvesen, Vatten et al. 1992; Salvesen, Jacobsen et al. 1993; Salvesen, Vatten et al. 1994).(2,3,4,5). This effect is significant because it implies that ultrasound can change the lateralization of the brain, which represents a significant shift in brain development. At the time of these studies in the early 90’s, ultrasound output was much lower, and examinations much shorter than today. Recent FDA regulation allows for a delivery of 8 times higher intensity!
In another study (Keiler, 2001)(6), left-handedness and prenatal ultrasound was studied in a cohort of men born in Sweden between 1973 and1978 who enlisted for military service. One group comprised of 6,585 men were born in hospitals that used ultrasound routinely (the “exposed” group). The other group, 172, 537 men, were born in hospitals without ultrasound (“unexposed” men).
Among men born between 1973 to 1975, no difference was found in rate of left-handedness between the exposed and unexposed groups.
As the use of prenatal ultrasound increased between 1976 and 1978, left-handedness in the “exposed group” increased 30 percent above the normal hereditary incidence; furthermore, when mothers received more than one ultrasound, there was a greater incidence of left-handedness in their offspring.(7)
On her “The Healthy Home Economist” website, Sarah points out that premature babies are five times more likely to be left-handed, and that the brain of the developing male fetus develops more slowly than the female, and puts boys at greater risk for ultrasound injury.
Something to think about.
I’ll be back with a few more interesting studies I found later this week.