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 fetus 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.
Intrauterine growth restriction (IUGR), or fetal growth restriction, refers to poor growth of a fetus while in the womb during pregnancy. IUGR is defined by clinical features of malnutrition and evidence of reduced growth regardless of an infant's birth weight percentile. The causes of IUGR are broad and may involve maternal, fetal, or placental complications.
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.
Trophoblasts are cells that form the outer layer of a blastocyst. They are present four days after 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.
Oligohydramnios is a medical condition in pregnancy characterized by a deficiency of amniotic fluid, the fluid that surrounds the fetus in the abdomen, in the amniotic sac. It is typically diagnosed by ultrasound when the amniotic fluid index (AFI) measures less than 5 cm or when the single deepest pocket (SDP) of amniotic fluid measures less than 2 cm. Amniotic fluid is necessary to allow for normal fetal movement, lung development, and cushioning from uterine compression. Low amniotic fluid can be attributed to a maternal, fetal, placental or idiopathic cause and can result in poor fetal outcomes including death. The prognosis of the fetus is dependent on the etiology, gestational age at diagnosis, and the severity of the oligohydramnios.
Placental abruption is when the placenta separates early from the uterus, in other words separates before childbirth. It occurs most commonly around 25 weeks of pregnancy. Symptoms may include vaginal bleeding, lower abdominal pain, and dangerously low blood pressure. Complications for the mother can include disseminated intravascular coagulopathy and kidney failure. Complications for the baby can include fetal distress, low birthweight, preterm delivery, and stillbirth.
Antepartum bleeding, also known as antepartum haemorrhage (APH) or prepartum hemorrhage, is genital bleeding during pregnancy after the 28th week of pregnancy up to delivery.
A vertically transmitted infection is an infection caused by pathogens that use mother-to-child transmission, that is, transmission directly from the mother to an embryo, fetus, or baby during pregnancy or childbirth. It can occur when the mother has a pre-existing disease or becomes infected during pregnancy. Nutritional deficiencies may exacerbate the risks of perinatal infections.
Intrauterine hypoxia occurs when the fetus is deprived of an adequate supply of oxygen. It may be due to a variety of reasons such as prolapse or occlusion of the umbilical cord, placental infarction, maternal diabetes and maternal smoking. Intrauterine growth restriction may cause or be the result of hypoxia. Intrauterine hypoxia can cause cellular damage that occurs within the central nervous system. This results in an increased mortality rate, including an increased risk of sudden infant death syndrome (SIDS). Oxygen deprivation in the fetus and neonate have been implicated as either a primary or as a contributing risk factor in numerous neurological and neuropsychiatric disorders such as epilepsy, attention deficit hyperactivity disorder, eating disorders and cerebral palsy.
Placenta accreta occurs when all or part of the placenta attaches abnormally to the myometrium. Three grades of abnormal placental attachment are defined according to the depth of attachment and invasion into the muscular layers of the uterus:
- Accreta – chorionic villi attached to the myometrium, rather than being restricted within the decidua basalis.
- Increta – chorionic villi invaded into the myometrium.
- Percreta – chorionic villi invaded through the perimetrium.
Chorionic villi are villi that sprout from the chorion to provide maximal contact area with maternal blood.
Placental insufficiency or utero-placental insufficiency is the failure of the placenta to deliver sufficient nutrients to the fetus during pregnancy, and is often a result of insufficient blood flow to the placenta. The term is also sometimes used to designate late decelerations of fetal heart rate as measured by cardiotocography or an NST, even if there is no other evidence of reduced blood flow to the placenta, normal uterine blood flow rate being 600mL/min.
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.
Velamentous cord insertion is a complication of pregnancy where the umbilical cord is inserted in the fetal membranes. It is a major cause of antepartum hemorrhage that leads to loss of fetal blood and associated with high perinatal mortality. In normal pregnancies, the umbilical cord inserts into the middle of the placental mass and is completely encased by the amniotic sac. The vessels are hence normally protected by Wharton's jelly, which prevents rupture during pregnancy and labor. In velamentous cord insertion, the vessels of the umbilical cord are improperly inserted in the chorioamniotic membrane, and hence the vessels traverse between the amnion and the chorion towards the placenta. Without Wharton's jelly protecting the vessels, the exposed vessels are susceptible to compression and rupture.
A placental disease is any disease, disorder, or pathology of the placenta.
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.
Placental villous immaturity is chorionic villous development that is inappropriate for the gestational age.
Ureaplasma urealyticum is a type of bacteria that can cause infection of the urinary tract and vagina. It can be passed from mother to infant during birth, or be sexually transmitted. Ureaplasma urealyticum can be found in a majority of sexually active people, most of whom are asymptomatic. It can also be found in cultures in cases of pelvic inflammatory disease. It is not a commensal of the healthy uterine or amniotic microbiome. Infection with U. urealyticum can contribute to neonatal infection and negative birth outcomes.
Breus' mole is a massive, subchorionic, tuberous hematoma, formed out of maternal blood in the uterus in pregnancy. It was first described by Karl Breus in 1892.
Massive perivillous fibrin deposition refers to excessive deposition of fibrous tissue around the chorionic villi of the placenta. It causes reduced growth of the foetus, and leads to miscarriage in nearly 1 in 3 pregnancies affected. There are typically no symptoms, and it is rarely detected before birth. The cause is unknown, but may be autoimmune. Diagnosis is based on the histology of the placenta. There are currently no known treatments. MPFD is very rare, but recurrence is around 18% in those affected.
