Wednesday, January 26, 2011

Sinistrality and Ultrasound

Dear Cindi and Birth Peeps,
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.



  1. I forgot to add my citations!
    1 Sarah ( Sept 28, 2010). Dopplers are a form of ultrasound. Referencing an article in Epidimiology 2001 on her website:

    2 Salvesen, K. A., L. S. Bakketeig, et al. (1992). "Routine ultrasonography in utero and school performance at age 8-9 years." Lancet 339(8785): 85-9.

    3 Salvesen, K. A., G. Jacobsen, et al. (1993). "Routine ultrasonography in utero and subsequent growth during childhood." Ultrasound Obstet Gynecol 3(1): 6-10.

    4 Salvesen, K. A., L. J. Vatten, et al. (1994). "Routine ultrasonography in utero and speech development." Ultrasound Obstet Gynecol 4(2): 101-3.

    5 Salvesen, K. A., L. J. Vatten, et al. (1992). "Routine ultrasonography in utero and subsequent vision and hearing at primary school age." Ultrasound Obstet Gynecol 2(4): 243-4, 245-7.

    6 Keiler, Halle (2001, Nov.). Sinistrality: a side effect of prenatal sonography—a comparative study of young men. Epidemiology. 12(6); 618-623.

    7 Sarah. (2010, Sept).

  2. Years ago(probably 4 years ago?), I read an article in Parents Magazine that said research showed that there was some correlation between the way your hair spirals on the back of your head and handedness - I believe clockwise is right-handed, and counterclockwise is either right- or left-handed. We do have the left-handedness gene in our family, but although my son's hair spirals the "wrong" way for left-handedness, he is left-handed. I always attributed this to the somewhat excessive ultrasounds I had during his pregnancy due to an ovarian cyst (and some unfounded concern that it would inhibit his growth). He was also born 6weeks early due to that cyst torsing, so I guess that didn't help either!

    Anyways, I find this to be such an important topic, so thank you!!

  3. So interesting. Thanks for posting! I guess I was wise to follow my gut and avoid ultrasounds during my first pregnancy. I did the same until my six months into my second pregnancy when my midwife deemed it medically necessary because of my rapid expansion. Lo and behold, that's how we found out I was carrying twins.

  4. Interesting, but too many confounders to believe for sure.
    The rise can likely also be attributed to the increase social acceptance of left handedness.
    In the Swedish study, there could have been many confounders. For example, increased heredity in the exposed group (did they look at this?), different exposures (diet, environmental, toxins), age of mothers/fathers, etc...the list goes on.
    Ultrasound has helped a lot of babies (e.g. diagnosing placenta previa, oligohydramnios, etc.) and significantly improved maternal care over the years.
    I think the brain is way too complex for such a simple explanation.

  5. Ultrasound is an amazing tool, but we don't know what's happening for babies while we are using it. Care providers need to respect the fact that we don't know what the effects of ultrasound are. There isn't sufficient evidence to support it's safety. Strangely, there hasn't been a lot of money put into studying the effects of this common procedure. Care providers who do respect this lack of knowledge still use ultrasound as a tool, but do it judiciously. Only when its medically necessary. And they are diligent at learning and practicing the arts of palpitation and pelvimetry, so that these important tools are not lost, and we can rely less on ultrasound. We also must remember that a doppler is an ultrasound. They should be used judiciously as well. And doctors/midwives have a responsibility to keep up to date on possible effects of all interventions used, so they can truly give informed consent to parents. Parents need to know ultrasound may not be safe, so they aren't headed to the mall every week to see their baby on a 3-D ultrasound machine! Seriously! Saying that this country overuses ultrasound is an understatement!
    I was reading Dr. Sear's "The pregnancy book" today and was impressed that he gave a decent explanation of what ultrasound does, why it may come with side effects, and why it should be used as a diagnostic tool, as the name implies, not so we can see the baby, again, and have a picture of it.