Infant resuscitation is associated with an increased risk of left-handedness.

The etiology of left lateral preference is not well understood, but some studies have suggested that it can be caused by complications at birth. The authors used data from the Child Health and Development Study, a large prospective study of pregnancy and child development conducted 1959-1966 in the San Francisco Bay Area of California, to examine the association between specific birth stressors and hand and foot preference. The study population consisted of 6,968 5-year-olds with no severe congenital abnormalities, and the authors controlled for potential demographic confounders and familial left-handedness. Infants who required resuscitation after delivery or who were twins or triplets were about twice as likely to demonstrate left hand preference at age 5 years (odds ratio (OR) = 1.8, 95% confidence interval (CI) 1.3-2.5, and OR = 2.2, 95% CI 1.2-4.0, respectively). Left-footedness was also significantly associated with the same stressors. No other individual stresses were significantly associated with left-lateral preference, and a composite measure indicated only a weak association. Although males, blacks, and those with left-handed siblings are more likely to show left lateral preference, these variables do not confound the association between birth stress and left lateral preference. These results indicate that specific types of birth stress are strongly associated with left hand and foot preference; however, much of the left laterality in non-clinical populations remains unexplained.