Implantation of the PLACENTA in the bottom part of the UTERUS adjacent to or over the CERVIX. The condition may cause few problems during pregnancy or labour; it may, however, cause vaginal bleeding late in pregnancy or hinder vaginal delivery of the baby and this may necessitate obstetric intervention.
a condition in which the placenta is situated wholly or partially in the lower and noncontractile part of the uterus. When this becomes elongated and stretched during the last few weeks of pregnancy, and the cervix becomes stretched either before or during labour, placental separation and haemorrhage will occur. The cause is not known. In the more severe degrees of placenta praevia, where the placenta is situated entirely before the presenting part of the fetus, delivery must be by Caesarean section. In lesser degrees of placenta praevia, vaginal delivery may be considered.
The thick, spongy, disc-like mass of tissue which connects the EMBRYO with the inner surface of the UTERUS, the embryo otherwise lying free in the amniotic ?uid (see AMNION). The placenta is mainly a new structure growing with the embryo, but, when it separates, a portion of the inner surface of the womb – called the maternal placenta – comes away with it. It is mainly composed of loops of veins belonging to the embryo, lying in blood-sinuses, in which circulates maternal blood. Thus, although no mixing of the blood of embryo and mother takes place, there is ample opportunity for the exchange of ?uids, gases, and the nutrients brought by the mother’s blood. The width of the full-sized placenta is about 20 cm (8 inches), its thickness 2·5 cm (1 inch). One surface is rough and studded with villi, which consist of the loops of fetal veins; the other is smooth, and has implanted in its centre the umbilical cord, or navel string, which is about as thick as a ?nger and 50 cm (20 inches) long. It contains two arteries and a vein, enters the fetus at the navel, and forms the sole connection between the bodies of mother and fetus. The name ‘afterbirth’ is given to the structure because it is expelled from the womb in the third stage of labour (see PREGNANCY AND LABOUR).... placenta
Placental bleeding after the 24th week of pregnancy, which may result in complete or partial detachment of the placenta from the wall of the womb. The woman may go into shock. The condition is sometimes associated with raised blood pressure and PRE-ECLAMPSIA. (See also PREGNANCY AND LABOUR.)... abruptio placenta
a condition in which the placenta is abnormally strongly attached to the wall of the uterus with superficial penetration of chorionic *villi into the underlying *myometrium. Women with *placenta praevia and at least one previous Caesarean delivery are considered to be at high risk for placenta accreta. When placenta accreta is thought to be likely, consultant obstetric and anaesthetic input are vital in planning and conducting the delivery. Radiological input with temporary uterine balloon tamponade may be considered, and methotrexate has been used. The risk of haemorrhage, blood transfusion, and hysterectomy should be discussed. In placenta increta the chorionic villi extend into the myometrium; a placenta percreta occurs where the chorionic villi penetrate through the myometrial wall and can invade the bladder. An emergency hysterectomy is usually necessary in these rare cases.... placenta accreta
an uncommon but potentially disastrous complication of delivery, occurring in about 1 in 5000 deliveries, when unprotected fetal vessels run across the *lower uterine segment and cervix in front of the presenting part of the fetus. It is associated with a velamentous insertion of the cord (where the umbilical cord inserts directly into the membranes rather than the placenta) and in cases with normal cord insertion when the vessels run between the two lobes of a bilobed placenta. Vessels unsupported by placental tissue or the umbilical cord can tear when the cervix dilates or the membranes rupture, causing rapid fetal haemorrhage. Immediate Caesarean section to save the baby from *exsanguination is indicated. Fetal mortality for cases not recognized before the onset of labour is very high; appropriate use of prenatal ultrasonography may prevent perinatal death.... vasa praevia
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