Sex differences in brain growth emerge in the wombThis study addresses the age-old question of whether nature plays a role in shaping sex differences in the brainAlex TsompanidisCambridge researchers have revealed a detailed picture of how the human brain grows from mid-pregnancy through the first weeks after birth and identified that sex differences in brain growth are apparent from mid-pregnancy onwards.There has long been debate over exactly how early in human brain development sex differences first emerge, and what causes them. Our study has documented the presence of prenatal sex differences in the growth of the human brain. "The next step is to test if the observed sex differences in human brain growth are driven by prenatal sex steroid hormones, such as testosterone and estrogen. For example, the early sex differences in the brain may be due to prenatal sex steroids, and autistic people are exposed to elevated levels of prenatal sex steroid hormones. Mapping brain growth and sex differences across prenatal to postnatal development.