A window for the study of prenatal sex hormone influences on postnatal development.

In humans, the influence of prenatal sex hormones on the fetal brain and subsequent postnatal development has had limited study because of the apparent inaccessibility of hormone levels in normal fetuses. We propose that amniotic fluid obtained via midtrimester amniocentesis can be assayed for fetal hormone levels during the period thought to be important for sexual differentiation of the brain. Amniotic fluid samples from midgestation (N = 70) were assayed for levels of testosterone and follicle-stimulating hormone, and significant sex differences were observed (ps less than .001), with some degree of overlap between the sexes. The possibility of applying hormone levels obtained from amniotic fluid to the study of postnatal development is discussed.