Such placentas are described as bilobed/bilobular/bipartite, trilobed/trilobular/tripartite, and so on. If there is a clearly discernible main lobe and auxiliary lobe, the latter is called a succenturiate placenta. Sometimes the blood vessels connecting the lobes get in the way of fetal presentation during labor, which is called vasa previa. Gene and protein expression
About 20,000 protein coding genes are expressed in human cells and 70% of these genes are expressed in the normal mature placenta. Some 350 of these genes are more specifically expressed in the placenta and fewer than 100 genes are highly placenta specific. The corresponding specific proteins are mainly expressed in trophoblasts and have functions related to female pregnancy. Examples of proteins with elevated expression in placenta compared to other organs and tissues are PEG10 and the cancer testis antigen PAGE4 and expressed in cytotrophoblasts, CSH1 and KISS1 expressed in syncytiotrophoblasts, and PAPPA2 and PRG2 expressed in extravillous trophoblasts. Physiology
Development
The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium, very early on in pregnancy at about week 4.The outer layer of the late blastocyst, is formed of trophoblasts, cells that form the outer layer of the placenta. This outer layer is divided into two further layers: the underlying cytotrophoblast layer and the overlying syncytiotrophoblast layer. The syncytiotrophoblast is a multinucleated continuous cell layer that covers the surface of the placenta. It forms as a result of differentiation and fusion of the underlying cytotrophoblasts, a process that continues throughout placental development.
Drug and alcohol use can contribute to pruritus as well so it is worthwhile to gather a social history. Those who use cocaine and amphetamines may experience pruritus due to feelings of abnormal cutaneous sensations called delusions of parasitosis, also known as "meth mites". Opioid users can also experience pruritus so examining a patients medication list can be beneficial. Diagnostic criteria
The French Psychodermatology Group is a subgroup of the French Society of Dermatology made up on psychiatrists, dermatologists and psychologists. They met in 2007 to propose diagnostic criteria for this disease in hope of preventing further misdiagnosis of this condition. They believed the term "functional itch disorder" was the best phrase to describe this condition, avoiding the use of the word "psychogenic". To diagnose a patient with functional itch disorder, the patient should meet three required criteria and three of seven optional criteria.Diagnostic Criteria:
3 Required criteria
Localized or generalized pruritus without a primary skin lesion
Chronic pruritus, characterized as being greater than 6 weeks
There is no somatic cause present
7 Optional criteria (need 3 to diagnose)
A chronological relationship of pruritus with one or several life events that can have psychological consequences
Changes during the nighttime
More present during rest or inaction
There is a coupled psychological disorder
Pruritus that could be improved with pyschotropic drugs
Pruritus that could be improved by psychotherapies

Treatment
The treatment for this condition has not been well studied but the most common options are psychotherapy and medicines geared toward psychiatric conditions. Stress reduction and relaxation techniques have also been shown to be helpful for alleviating this condition.