Complications of the Placenta: An Overview

Placental disorders are complication of pregnancy that involve the placenta. This is an organ that exists from the late first trimester of pregnancy, until birth, when it is delivered with the baby. During pregnancy, the placenta supports the fetus by functioning in respiration (it enables exchange of gases between the maternal and fetal blood), excretion (waste products move from the fetal blood vessels to maternal blood vessels), immunity (it allows antibodies from the mother to transfer from the maternal blood into the fetal blood), nutrition (nutrients move from maternal blood to fetal blood), and endocrine function (it produces human chorionic gonadotropin, estrogen, and progesterone).

The placenta is involved in certain disorders manifesting as maternal disease throughout the body, notably preeclampsia (a condition characterized by high blood pressure and problems with one or more internal organs, especially the kidney) and HELLP syndrome (a condition characterized by high blood pressure, problems with blood cells, and problems with the liver and other organs). However, pregnancy and delivery are also frequently disrupted by placental complications that are localized to the placenta itself. Such conditions include the following:

Placenta previa: This is a condition in which the placenta is low in the uterus. Placenta previa is subcategorized by the particular position of the placenta, namely whether it is merely close to the cervical os (the opening of the cervix) or partly or fully covering the os. In any of these cases, placenta previa can cause bleeding during pregnancy and delivery, as the fetus is pushing down against the endocervical canal. Should the woman go into labor, severe bleeding becomes more likely as the placenta is blocking the birth canal. Given it’s obstructive nature, placenta previa also increases the likelihood of preterm birth.

Risk factors for placenta previa include a previous cesarean delivery, uterine surgery, and multiple gestation, meaning that you are carrying twins or a higher order pregnancy. Placenta previa is typically diagnosed through ultrasound and can be managed with bed rest, close monitoring, intravenous fluids, and transfusion of blood products in the event of hemorrhage. Cesarean delivery is required and generally is planned to be performed around 36 to 37 weeks gestation for a singleton pregnancy (earlier for twins). This is to reduce the risk of spontaneous labor that would cause bleeding as the fetus moves into or through the cervix.

Placenta accreta: This is a condition in which the placenta is attached too deeply into the uterus and consequently can become difficult to separate from the uterine wall after delivery. Normally, the placenta is attached only through the endometrium, the innermost layer of uterus. In placenta accreta, however, the placenta reaches through the endometrium and is up against the myometrium (the muscular layer of the uterus) or penetrates into the myometrium. The condition is subcategorized based on how deep the penetration goes. During and following delivery of the baby, placenta accreta can cause severe bleeding, while also elevating the risk of uterine rupture. This is because, when the placenta does finally separate from the placenta, it can take parts of the myometrium with it.

Risk factors for placenta accreta include a previous previous placenta accreta, previous cesarean delivery, uterine surgery, and multiple gestation. Typically, the condition is diagnosed through ultrasound and in such cases doctors will plan for a caesarean birth. In cases of hemorrhage, the mother can be treated with medications to control bleeding, intravenous fluids, and, if needed, transfusion of blood products. In severe cases, doctors may need to perform a cesarean hysterectomy, meaning that the baby is delivered surgically and the uterus is removed.

Abruptio placentae: Also known as placental abruption, this is a condition in which the placenta separates from the uterine wall at any time prior to delivery. Such abruption can cause severe bleeding and fetal distress and also increases the risk of preterm birth and stillbirth. Risk factors for placental abruption include high blood pressure, smoking and use of certain other drugs such as cocaine, and multiple gestation. Placental abruption is typically diagnosed through ultrasound and fetal monitoring, and it is usually managed with immediate caesarean delivery. As with placenta previa and accreta, hemorrhage can be treated with fluid resuscitation and, if needed, transfusion of blood products.

Vasa previa: Vasa previa is condition in which fetal blood vessels of the placenta and/or umbilical cord membranes run unprotected near, or through the cervix. Normally, the placenta exists as a single structure, from which the umbilical cord emerges and enters the fetus. Also normally, the cord blood vessels —consisting of the umbilical vein carrying oxygenated blood from the placenta to the fetus and two umbilical arteries carrying deoxygenated blood from the fetus to the placenta— are surrounded by a protective substance called Wharton’s Jelly. In one type of vasa previa, however, parts of these vessels are present without the Wharton’s Jelly covering, so that are vulnerable to rupture. In another type of vasa previa, the placenta includes an accessory lobe, meaning that a portion of the organ is physically separate from the rest of it, but the accessory lobe is connected to the rest of the placenta by placental blood vessels. As with umbilical vessels without the jelly, blood vessels running between placental lobes can run through or near the cervix and are vulnerable to rupture.

Risk factors for vasa previa include previous vasa previa, multiple gestation, and a previous cesarean delivery. Vasa previa can cause bleeding and fetal distress. As with the other conditions, bleeding can necessitate intravenous fluids, and, when severe, transfusion of blood products. As you may suspect from reading about the other conditions, cesarean delivery.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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