The authors look at samples of amniotic fluid taken during amniocentesis at 16 weeks' gestation, and relate the fetal level of testosterone (which is present in... » 

The authors look at samples of amniotic fluid taken during amniocentesis at 16 weeks' gestation, and relate the fetal level of testosterone (which is present in fetuses of both sexes, although in different quantities) to behavior at ages 1, 2, and 4 years. They argue that the amniotic fluid provides a window into the child's past -- a chemical record of that child's time in the womb -- that allows informed prediction about the child's future brain, mind, and behavior. «