Sounding out lefties in the womb.

Sounding out lefties in the womb 

Should we buy blue of pink? Routine fetal ultrasound scanning has taken some of the anxiety out of this gender guessing for many prospective parents. Now, for the first time, researchers are using the same sonographic techniques to uncover the earlierst hints of a baby's handedness.

Scanning 224 fetuses with ultrasound, psychologist Peter G. Hepper and colleagues at the Queen's University in Belfast, Ireland, discovered that 94.6 percent preferred sucking their right thumb. Just 12 fetuses, or 5.4 percent, favored the left thumb, the team reports in the Oct. 4 NATURE.

"We have clear evidence of handedness in the womb," Hepper told SCIENCE NEWS. These results underscore the theory that most lefties inherit their left-handed tendency rather than pick up the preference by watching mom and dad, he says.

Lefties identified in the womb were also more likely to turn their head to the left after birth, one very early sign of left handedness, Hepper notes. The researchers suspect these newborn southpaws will go on to favor their left hand later in life and plan to test this theory by monitoring these same babies as they develop motor skills that will allow them to grasp toys and other objects with either hand.