Psychology researchers at B.C.’s Simon Fraser University have shed some light on “mommy brain,” the well-known state of forgetfulness that often affects pregnant and new moms. Neil Watson and Claire Vanston studied 39 Vancouver women and found that those giving birth to boys did much better on memory tests requiring listening, computational and visualization skills than those having girls. The effect of the baby’s sex on memory was “large and enduring,” says Watson, beginning as early as 10 weeks’ gestation and lasting well past weaning. “We did not set out to examine the effect of fetal sex on a mother’s cognition, so the results took us completely by surprise,” he says. It’s unclear what exactly causes this disparity—but human chorionic gonadotropin (hCG), the hormone measured by pregnancy tests and reportedly higher in women carrying girls—may play a role.