The placenta is a temporary fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate maternal and fetal circulations, and is an important endocrine organ producing hormones that regulate both maternal and fetal physiology during pregnancy. The placenta connects to the baby via the umbilical cord, and on the opposite aspect to the maternal uterus in a species dependent manner. In humans, a thin layer of maternal decidual (endometrial) tissue comes away with the placenta when it is expelled from the uterus following birth. Placentas are a defining characteristic of placental mammals, but are also found in marsupials and some non-mammals with varying levels of development.
The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles (amniotes). It develops from an outer fold on the surface of the yolk sac, which lies outside the zona pellucida, known as the vitelline membrane in other animals. In insects it is developed by the follicle cells while the egg is in the ovary.
Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease there may be red blood cell breakdown, a low blood platelet count, impaired liver function, kidney dysfunction, swelling, shortness of breath due to fluid in the lungs, or visual disturbances. Pre-eclampsia increases the risk of undesirable outcomes for both the mother and the fetus. If left untreated, it may result in seizures at which point it is known as eclampsia.
Gestational hypertension or pregnancy-induced hypertension (PIH) is the development of new hypertension in a pregnant woman after 20 weeks' gestation without the presence of protein in the urine or other signs of pre-eclampsia. Gestational hypertension is defined as having a blood pressure greater than 140/90 on two occasions at least 6 hours apart.
Trophoblasts are cells that form the outer layer of a blastocyst. They are present four days post-fertilization in humans. They provide nutrients to the embryo and develop into a large part of the placenta. They form during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg to become extraembryonic structures and do not directly contribute to the embryo. After gastrulation, the trophoblast is contiguous with the ectoderm of the embryo and is referred to as the trophectoderm. After the first differentiation, the cells in the human embryo lose their totipotency and are no longer totipotent stem cells because they cannot form a trophoblast. They are now pluripotent stem cells.
Molar pregnancy is an abnormal form of pregnancy in which a non-viable fertilized egg implants in the uterus and will fail to come to term. A molar pregnancy is a gestational trophoblastic disease which grows into a mass in the uterus that has swollen chorionic villi. These villi grow in clusters that resemble grapes. A molar pregnancy can develop when a fertilized egg does not contain an original maternal nucleus. The products of conception may or may not contain fetal tissue. It is characterized by the presence of a hydatidiform mole. Molar pregnancies are categorized as partial moles or complete moles, with the word mole being used to denote simply a clump of growing tissue, or a growth.
Choriocarcinoma is a malignant, trophoblastic cancer, usually of the placenta. It is characterized by early hematogenous spread to the lungs. It belongs to the malignant end of the spectrum in gestational trophoblastic disease (GTD). It is also classified as a germ cell tumor and may arise in the testis or ovary.
Gestational trophoblastic disease (GTD) is a term used for a group of pregnancy-related tumours. These tumours are rare, and they appear when cells in the womb start to proliferate uncontrollably. The cells that form gestational trophoblastic tumours are called trophoblasts and come from tissue that grows to form the placenta during pregnancy.
Gestational choriocarcinoma is a malignant trophoblastic tumour arising from any gestational event during pregnancy in the reproductive female. Women with gestational choriocarcinoma may present with abnormal vaginal bleeding, persistent markedly elevated βhCG, or a history of prior pregnancy. Most patients develop gestational choriocarcinoma shortly after gestational anomalies, but pathology may occur after a long latency of years. It may occur during pregnancy. Often, it happens after a growth of some sort in the womb
Gestational trophoblastic neoplasia (GTN) is group of rare diseases related to pregnancy and included in gestational trophoblastic disease (GTD) in which abnormal trophoblast cells grow in the uterus. GTN can be classified into benign and malignant lesions. Benign lesions include placental site nodule and hydatidiform moles while malignant lesions have four subtypes including invasive mole, gestational choriocarcinoma, placental site trophoblastic tumor (PSTT) and epithelioid trophoblastic tumor (ETT). The choriocarcinoma has 2 significant subtypes including gestational and non-gestational and they are differentiated by their different biological feature and prognosis. Signs and symptoms of GTN will appear vary from person to person and depending upon the type of the disease. They may include uterine bleeding not related to menstruation, pain or pressure in pelvis, large uterus and high blood pressure during pregnancy. The cause of this disease is unknown but the identification of the tumor based on total beta-human chorionic gonadotropin (β-hCG) in the serum.
Jaagsiekte sheep retrovirus (JSRV) is a betaretrovirus which is the causative agent of a contagious lung cancer in sheep, called ovine pulmonary adenocarcinoma.
Confined placental mosaicism (CPM) represents a discrepancy between the chromosomal makeup of the cells in the placenta and the cells in the fetus. CPM was first described by Kalousek and Dill in 1983. CPM is diagnosed when some trisomic cells are detected on chorionic villus sampling and only normal cells are found on a subsequent prenatal test, such as amniocentesis or fetal blood sampling. In theory, CPM is when the trisomic cells are found only in the placenta. CPM is detected in approximately 1-2% of ongoing pregnancies that are studied by chorionic villus sampling (CVS) at 10 to 12 weeks of pregnancy. Chorionic villus sampling is a prenatal procedure which involves a placental biopsy. Most commonly when CPM is found it represents a trisomic cell line in the placenta and a normal diploid chromosome complement in the baby. However, the fetus is involved in about 10% of cases.
Placental growth factor is a protein that in humans is encoded by the PGF gene.
Achaete-scute complex homolog 2 (Drosophila), also known as ASCL2, is an imprinted human gene.
A placental disease is any disease, disorder, or pathology of the placenta.
Intermediate trophoblast is a distinct subtype of trophoblastic tissue that arises from the cytotrophoblast.
Villitis of unknown etiology (VUE), also known as chronic villitis, is a placental injury. VUE is an inflammatory condition involving the chorionic villi. VUE is a recurrent condition and can be associated with intrauterine growth restriction (IUGR). IUGR involves the poor growth of the foetus, stillbirth, miscarriage, and premature delivery. VUE recurs in about 1/3 of subsequent pregnancies.
A placental site nodule (PSN) is benign remnant from a previous pregnancy.
Early pregnancy bleeding refers to vaginal bleeding before 24 weeks of gestational age. If the bleeding is significant, hemorrhagic shock may occur. Concern for shock is increased in those who have loss of consciousness, chest pain, shortness of breath, or shoulder pain.
Extravillous trophoblast or, abbreviated, EVT, are one form of differentiated trophoblast cells of the placenta. They are invasive mesenchymal cells which function to establish critical tissue connection in the developing placental-uterine interface. EVTs derive from progenitor cytotrophoblasts (CYT), as does the other main trophoblast subtype, syncytiotrophoblast (SYN).
