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Advances in obstetrical ultrasound, combined with ancillary magnetic resonance imaging and rapid molecular testing of amniotic fluid, have greatly improved the diagnostic capabilities when assessing the fetus with suspected intrauterine growth restriction (IUGR). Placental villi are covered by the fetally derived epithelial layer termed villous trophoblast; this is a distinct lineage under separate transcriptional control from the extravillous trophoblast (EVT) in mammalian placentae. The maternal-fetal interface, or decidua, is rich in cell lineages of the maternal immune system, in particular large granular lymphocytes and uterine natural killer (NK) cells. The net effect of abnormal maternal perfusion of the placental villi is one or more of the following: spiral artery thrombosis and unstable perfusion. The developmentally abnormal placenta, characterized by decidual bed pathology, structurally abnormal villi with defective or damaged areas of syncytiotrophoblast is prone to thrombosis.
The development of effective anticoagulant drugs available for use in pregnancy has resulted in dramatic improvements for a number of potentially life-threatening conditions. These include the treatment and prevention of venous thromboembolism and the thrombotic complications of antiphospholipid antibody syndrome, as well as the management of pregnant women with mechanical heart valves. The most commonly used class of drug includes heparin, a highly-charged macro-molecule that does not cross the placenta, in contrast to the potentially teratogenic and fetotoxic oral drug warfarin. This review will focus on our current lack of understanding of the wider actions of heparin and examines the possibility that large numbers of pregnant women are presently being treated inappropriately with heparin.
Comparative studies of placentation across mammals have been greatly facilitated by the availability of phylogenetic trees for the entire range of placental mammals based on molecular data. The three basic placenta types defined by Grosser on grounds of increasing invasiveness epitheliochorial, endotheliochorial, and hemochorial have routinely served as a basis for comparative discussions. Primates differ starkly from all other placental mammal orders because the two extreme kinds of placentation are represented, while the moderately invasive is not. Reliable inference of the primitive condition is an essential starting-point for successful reconstruction of the evolution of placentation in placental mammals. Having considered the general background to evolution of the placenta in primates, it is now possible to focus specifically on catarrhines Old World monkeys, apes, and humans. The architecture of the placenta is notably different in New World monkeys (platyrrhines), which diverged from catarrhines at least 40 mya.