Invasive Trophoblast Implantation and Placentation

The Great ape route and depth of trophoblast invasion is unique among primates. In lower primates such as Old World monkeys and Gibbons, the cytotrophoblast invades via the endovascular route and transforms the endometrial segments of the arteries. In gorilla, chimpanzee and human, there is additional invasion via the interstitial route as well as spiral artery transformation through the inner third of the myometrium. This unique placentation and associated failures may be the root cause of several pregnancy and delivery related disorders such as recurrent miscarriage, fetal growth restriction, preeclampsia, preterm birth, and postpartum hemorrhage. Given the numerous changes that had to occur at the genetic, cellular, and anatomic levels for this unique trophoblast implantation to evolve, and the fact that there are human specific changes in pathways known to play a role in Great ape trophoblast invasion (e.g. KIRs, HLAs, and Siglecs), it is likely that there are human specific changes within the process.