I was having a casual conversation at a family get together a while ago about left-handedness and Dr. D's theory that it is related to stress in the womb affecting the development of the part of the brain controlling coordination and dexterity. Little did I know that my niece sitting next to me is left-handed and her mother (my sister) was sitting nearby questioning that theory based upon her pregnancy. My sister did not feel she had a difficult pregnancy medically speaking, although she was a bit nauseous and didn't have a big appetite early on.

Contrast that with women you know that had rough or unplanned pregnancies that experienced multiple difficulties throughout their pregnancies that ended up with right handed children. Certainly, there are other signs such as asymetry that point to fetal stress, so why is this not consistently the case in left-handedness?

Is it perhaps that there is one limited period in a woman's pregnancy where this particular development of the brain is the most vulnerable to stress and therefore left-handedness is determined?

Here's another interesting tidbit. One of my twin sons is a lefty (and slightly ambidextrous), the other strictly right handed. My left-handed Explorer son also has more physical asymetry than Nomad son. There's no doubt their birthmother experienced a fair amount of stress during her pregnancy with them.

Any lefties or parents of lefties care to share their thoughts and opinions?

Check for symmetry of fingerprint patterns as well.

http://www.ncbi.nlm.nih.gov/pubmed/22332424

I am left handed and asymmetrical in prints. Dr. D asked if my mom was doing summersaults with me. She told me her pregnancy was very happy and stress free.... except that she was on medication for ulcerative colitis.

She also worked at a dental office a few years prior and they regularly "played" with mercury.

I kind of wonder now if the colitis was related to her body trying to rid herself quickly of that toxin because of the pregnancy. Just a thought.

I was very sensitive to a tiny filling I had replaced.

As far as I know, I am the only lefty in my family.  I am strong left dominant.  I do not know of any fetal stress I might have experienced, but there is a possibility that my mother did try to keep her weight down while pregnant.

My father was a leftie.  He was born to dirt-poor homesteaders in Appalachia.  His parents worked harder than hard, farming, plowing with horses, living in a house with no electricity or running water, apart from the hand pump outside the door.  They grew all their own veggies, including the fruit from their orchard, slaughtered their own meat, eggs from their chickens.  Maybe exhaustion affected his mother.

I'm ambidextrous. My mom was under a lot of stress while pregnant with me. She was living with her in-laws while Dad was fighting in the war. Very stressful she told me.

My husband [pos A] and I are both mainly right handed but sometimes favour using our left hand, some games, computer mouse,  .... but not for writing.

All 3 of our children, all A's are left handed.  I was under a lot of stress with the first, possibly some the second, but not with the third.  All pregnancies and births were normal with little nausea - only vomited once during first preg and never with the others.

Our middle child, our only daughter, married to an O right hander has 2 left handed sons - no idea of BT.  Other grandson, oldest boy's son, is still ambidextrous but time will tell.

Interesting observations

I think the theory is not absolute, but what I read(elsewhere)was that if left-handedness is not hereditary, it may be caused by stress during pregnancy.
My parents weren't happy, so that was the apparent stress with me. I also surely wasn't planned as I came too soon after my older sibling. As far as I know, my mom had a physically easy pregnancy & fast delivery with me. My sister was breech, but delivered with forceps (thankfully not a c-section).
But surely(mostly?) there are stressful pregnancies with right-handed kids born. There are other ways to manifest the stresses.
Only one set of my fingerprints isn't symmetrical.
We are fearfully & wonderfully made in spite of problems our parents had!!

One of my brothers is a leftie; and there must have been some fetal stress, because he weighed under 5# at birth.

Both my husband (O) and I (A) are righties, but both of our kids(O's) are lefties. I had a very hard time conceiving, so I was on large doses of Clomid fertility pills. I was very stressed in the months preceding conception , but once pregnant I was blessed with great joy, and excellent health! So... was it the drugs, or the stress of trying to get pregnant that 'caused' the left handedness? My  oldest brother is a lefty, and I believe my Grandma was supposed to be, but her teachers forced her to switch.

I did a google search on the topic to see how much other information is out there on the subject. There are many different theories on left-handednes, but no one clear cause:

Stress hormones leading to oxygen deprivation
Fetal position in the womb
Sonograms, particularly in the 2nd and early 3rd trimester
Heredity (2 lefty parents have about a 30% chance of having lefty child)
Oxygen deprivation at birth

There were many articles that pointed to the correllation between asymmetry and left-handedness, which many of us already know. Also, these articles pointed to a higher incidence of learning disabilities in lefties, which I would agree with based upon my experience home schooling 2 left-handed children. I'm sure that isn't always the case, though.

I have a nephew that had some oxygen deprivation at birth who's a leftie.  My younger son is a leftie and I had a relatively easy pregnancy with him. Played tennis until a week or two before he was born. I had more stress with my older son since my mother in law died when I was just a couple of months along and I had some bleeding.  Interesting theory though.

This is epigenetic, not just genetic or just environmental. Some people are genetically  more "prone to" being left-handed, and only a small amount of stress in the womb can make that trait come about. Others are "less prone to" left-handedness, and a very stressful prenatal environment will show up in other ways. Some people may even be genetically left-handed, and will end up being left-handed even if everything "goes right" during the pregnancy- though I am curious if that's truly genetic or epigenetics "passed down" from one or both parents.

I remember reading about that, though I can't remember if it was from Dr D or another  book about epigenetics I found at the library. Some epigenetic things are caused by the parents' or even grandparents' experiences, not necessarily what the individual actually experienced in utero. It makes biological sense- say a women experienced a famine (or several famines) in her lifetime, but was well fed during her pregnancies? Shouldn't her children be equally prepared to survive famines as she is? Those same "famine surviving" adjustments lead to obesity and diabetes with today's access to food and processed carbs.

Ruthie,

Dr. D talked about the epigenetic factors explaining why women who experienced famine in their pregnancies often had children that became obese later in life (or sometimes early in life). The science behind it makes sense and is well documented. He explains that in detail in The Genotype Diet book, as well as some of research behind why fetal stress can cause left-handedness, though this still remains somewhat of a mystery.

When I was googling fetal stress and left-handedness the other day, some articles were making a strong correllation between learning disabilities and other signs of asymmetry related to left-handedness. While some studies show there is a causative genetic link to left-handedness, they couldn't conclude that was the only reason because approximately only 20%-40% of lefties were born to 2 left-handed parents. If genetics were the primary reason for left-handedness, then the percentages of children born to left-handed parents should be closer to 90%.

I think my left-handed niece I referred to probably inherited her left-handedness, due to the fact that my sister had a pretty easy pregnancy and she does not suffer from learning disabilities or low I.Q. But I still think my left-handed son and daughter probably suffered oxygen deprivation or fetal stress resulting in their left-handedness. They most certainly have learning apparent learning disabilities. My daughter also has cranio-facial abnormalities and my son has a lot of allergies, both of which were mentioned as common correllations with left-handedness.

I was remembering listening to a testimony a couple years ago when Tim Tebow was a rising star with the Denver Broncos. His parents talked of Tim being their "miracle baby" and just how truly amazing their story was. I don't remember all the details, but to make a long story short, there were no doctors during that time that gave them any hope she would give birth to a living, breathing baby. The mother had physical issues that put her at risk, and doctors were telling her to abort, or that the baby would most certainly die. I remember hearing that after giving birth to Tim, the doctors discovered the placenta was very abnormal and not attached to the uterine wall for an unknown period of time. Nobody could explained how Tim was born alive, but they knew it was divine intervention and that their prayers were answered. I'm saying all this because Tim is a left-handed quarterback and there was most certainly a lot of fetal stress and significant oxygen deprivation present before birth.