Left handedness in offspring as a function of maternal age at parturition

2,228 college freshmen were tested for their handedness. The age of their mother at the time of their birth was determined. The safest childbearing ages (17 to 24 years) were used as a reference point. The risk of the child being left-handed steadily increases as the mother's age at the time of delivery increases. If the mother is 35 to 39 years old when she gives birth, the likelihood of left-handed offspring is 69% higher. If the mother is over 40 the likelihood of left handed offspring is 128% higher.