The placenta is a key organ of pregnancy. It provides a connection between the developing fetus in the womb and the uterine walls of the mother. This placental connection is responsible for providing nutrients to the fetus, eliminating wastes generated by fetal growth, gas exchange for fetal respiration, immune defense factors and hormones that support pregnancy. The umbilical cord that connects the fetus to the uterus develops from the placental tissue.
The placenta is a fetomaternal organ, which means that it has both fetal and maternal parts. The fetal part of the placenta (technically known as chorion frondosum) develops from the blastocyst, whereas the maternal part of the placenta (technically known as decidua basalis) develops from the uterus. The blastocyst is the tissue from which the fetus develops. The placenta starts to develop as soon as the blastocyst burrows and implants into the uterine tissue.
Thereafter, the placenta keeps growing throughout pregnancy. The human placenta is a disc-shaped organ. The blood supply connecting the mother’s circulatory system to the fetal circulatory system is completely established by the end of the first trimester of pregnancy. The placenta does not let all substances and cells pass through. It acts as a barrier to the passage of many microbes.
However, despite the barrier function of the placenta, some infections are able to pass from the mother to the fetus. After the birth of the fully developed baby, the placenta separates from the uterine wall and is expelled. The expulsion of placenta usually occurs within thirty minutes after the birth of the baby. This phase of placental expulsion is also referred to as the third stage of labor.
What is an infected placenta?
Chorioamnionitis refers to a bacterial infection of the chorionic and amniotic membranes that surround the developing fetus. The amniotic fluid and the placenta may also get infected in this condition, leading to various complications such as preterm birth and serious infection of the fetus and the mother. Chorioamnionitis (also known as intra-amniotic infection or IAI) often occurs before or during labor, and is commonly associated with preterm births.
Bacteria that cause infection of the placenta usually reach this organ either by ascending through the vagina or through the blood supply from the mother. Infections caused by bacteria from the vagina are technically referred to as ascending infections, whereas infections caused via the mother’s bloodstream are referred to as hematogenous infections. Most ascending infections are usually caused by bacteria. However, hematogenous infections may be caused by non-bacterial pathogens as well.
Infection of the placenta causes infiltration of leukocytes into the infected region, resulting in cloudiness of the amniotic fluid. The infected tissue may also display vascular congestion and tissue swelling (technically referred to as villitis). Infection of placenta can lead to premature rupture of membranes (commonly abbreviated as PROM) and preterm labor. Maternal complications include pelvic abscess, bacteremia, postpartum hemorrhage, thromboembolism, and poor wound healing. Fetal complications include low apgar score indicating poor fetal development, pneumonia, sepsis, cerebral palsy, meningitis, seizures and death.
Read more on miscarriage.
Signs and Symptoms
The signs and symptoms that pregnant women with infected placenta may display varies on a case-to-case basis. Some patients may show only a few low-intensity symptoms, whereas others may display atypical symptoms. This may lead to missed diagnosis. The following are some of the signs and symptoms associated with placental infection:
- Tenderness in the abdomen or pelvic (uterine) area.
- A foul-smelling, yellowish or greenish discharge from the vagina.
- Rapid heart rate in both the mother (in excess of 100 beats per minute) and the fetus (more than 160 beats per minute).
- Fever (more than 100.4 °F).
Confirmed diagnosis of placental infection also requires a complete blood test to detect an increase in the white blood cell count. Sometimes, amniocentesis may be done to test for subclinical infection. However, amniocentesis is usually avoided as far as possible, since it may lead to further complications.
Read more on premature baby.
Causes of Infected Placenta
There are two main routes through which the placenta may become infected. The most common way is through the vaginal route. Ascending bacterial infections are the most common causes of infected placenta or chorioamnionitis. In fact, the bacterial species responsible for causing urogenital infections are also responsible for causing chorioamnionitis. The normal flora of the placenta is usually distinct from the microbes that cause chorioamnionitis.
Under normal circumstances, the microenvironment of the cervix and the vagina prevent pathogens from reaching the uterus. However, certain factors may promote the ascending bacterial infections. Such facilitating factors include poor urogenital hygiene, immunodeficiency (such as in HIV-positive mothers), and an anatomically short cervix. Frequent vaginal examinations during the final month of pregnancy also increase the risk of chorioamnionitis. Prolonged labor is another risk factor in developing chorioamnionitis.
The second route through which the placenta can get infected involves the maternal bloodstream (hematogenous route). Hematogenous infections of the placenta can be caused not just by bacteria, but also by other pathogens. The most common pathogenic causes of hematogenous placental infection include:
- Others like syphilis, listeriosis and tuberculosis
- Cytomegalovirus (commonly abbreviated as CMV)
- Herpes simplex virus (commonly abbreviated as HSV)
These hematogenous causes of placental infection are also referred to by the term TORCH (formed by stringing together the first letter of each of the above five groups of pathogens).
Treatment for Infected Placenta
Treatment of infected placenta or chorioamnionitis is mainly through antibiotics. The antibiotics used for the treatment are usually broad spectrum antibiotics. Intravenous route of administration is preferred to prevent both maternal and fetal complications of the infection. Due to the serious nature of the complications, the antibiotic therapy is usually started even before the confirmatory results of the culture test are known.
The treatment may continue even after the birth of the baby, and both the mother and the baby may be given different antibiotics. In case of acute chorioamnionitis, it may become necessary to induce immediate delivery. This is especially the case when signs of fetal distress are present. However, the immediate delivery option depends on the stage of the pregnancy, and is not possible in all cases of acute chorioamnionitis.