An anthropological perspective on the evolutionary context of preeclampsia in humans.

Preeclampsia/eclampsia is a dangerous condition unique to humans that is associated with an energetically expensive developing fetal brain and extremely invasive implantation of the trophoblast. We review here the evolutionary history of human pregnancy and childbirth to set a context for evolutionary hypotheses about the origin of preeclampsia. Humans are characterized by having large brains, bipedal locomotion and helpless newborns. These distinctive aspects of our biology arose independently but together constrain pregnancy and childbirth leading to an unusual mechanism of birth, cephalopelvic disproportion, shoulder dystocia, difficult labors, and neonates requiring high levels of parental care. Our cultural adaptation in the form of assistance during childbirth and intensive parental investment make it possible to balance those constraints. Preeclampsia probably arose only after the increase in human brain size and modern human mechanism of birth. Like the other risks of childbirth, preeclampsia also represents a risk associated with these distinctive aspects of human pregnancy and childbirth and is mitigated today by medical intervention. We speculate that, like assistance during childbirth, cultural intervention during pregnancy may extend into the past.