The mature placenta measures about 15 to 20 cm in when the placenta attaches too deeply into the uterine wall diameter and 2 to 3 cm in thickness, covers 25% to 30% but does not penetrate the myometrium. Placenta increta of the uterine surface, and weighs 500 g to 600 g at term. (about 15% of all cases) occurs when the placental villi The surface area of the villi of human placenta is estimated penetrate deep into the muscular layer of the myometrum. to be about 10 m2. The microvilli on the syncytiotrophoblast In the remaining 10% of all cases, placenta percreta pen-increase the effective area for metabolic exchange to more etrates through the entire uterine wall and attaches to an-than 90 m2. After birth, the uterus continues to contract, other organ such as the bladder, rectum, intestines, or reducing the luminal surface and inducing placental separa-large blood vessels. It is the most serious complication of tion from the uterine wall. The entire fetal portion of the pla-placentation and may cause rupture of the uterus and other centa, fetal membranes, and the intervening projections of complications related to its attachment. A retained abnordecidual tissue are released. During uncomplicated labor, mal placenta or placental fragments may cause massive the placenta separates from the uterine wall and is delivered postpartum bleeding and need to be manually removed. approximately 30 minutes after birth. Placenta increta and percreta are often treated by perform-
One of the most severe complications of labor results ing a hysterectomy. from abnormal placentation (abnormal attachment of After physiologic delivery of the placenta, the endomethe placenta on uterine wall). If decidual tissue during im-trial glands and stroma of the decidua basalis regenerate. plantation is disrupted, the placenta invades deep into the Endometrial regeneration is completed by the end of the uterine wall. This may cause one of the three clinical condi-third week postpartum except at the placental site, where tions, known as placenta accreta, placenta increta, or pla-regeneration usually extends for another three weeks. Durcenta percreta. Classification depends on the severity and ing the first week after delivery, remnants of the decidua deepness of the placental attachment. Placenta accreta, are shed and constitute the red-brown uterine discharge accounting for approximately 75% of all cases, occurs known as lochia rubra.
regulate maternal nutrient storage to the nutrient requirements of the fetus. It is also involved in transporting nutrients across the placental barrier from mother to the fetus.
 Other growth factors stimulate cytotrophoblastic growth (e.g., fibroblast growth factor, colony-stimulating factor [CSF-1], platelet-derived growth factor, and interleukins [IL-1 and IL-3]) or inhibit trophoblast growth and proliferation (e.g., tumor necrosis factor).
The vagina is a fibromuscular tube that joins internal reproductive organs to the external environment.
The vagina is a fibromuscular sheath extending from the cervix to the vestibule, which is the area between the labia minora. In a virgin, the opening into the vagina may be surrounded by the hymen, folds of mucous membrane extending into the vaginal lumen. The hymen or its remnants are derived from the endodermal membrane that separated the developing vagina from the cavity of the definitive urogenital sinus in the embryo.