An infection of the placenta is known as chorioamnionitis. This term actually describes an infection of the chorion, amnion, amniotic fluid and/or placenta. It is also known as an intra-amniotic infection. An infected placenta can jeopardize the pregnancy and even the health of the mother.
An infection in the placenta can develop when bacteria enter through the birth canal (ascending infection) or by reaching the placenta through the mother’s blood stream (hematogenous). Most ascending infections are due bacteria although other pathogens may be involved, especially in hematogenous infections. The amniotic fluid may become cloudy and purulent with infiltration by leukocytes. This causes swelling of the tissue (villitis) and vascular congestion.
The infection can lead to preterm labor and premature rupture of membranes (PROM). Other complications in the fetus may include a lower apgar score (< 3) upon delivery, sepsis, respiratory tract infections like pneumonia, meningitis, cerebral palsy, seizures and even death. The complications for the mother may include bacteremia, pelvic abscess, post partum hemorrhage, pelvic abscess, poor wound healing and infection and thromboembolism.
Causes of an Infected Placenta
Most cases are due to an ascending bacterial infection and often the same bacteria involved in other urogenital infections are responsible for chorioamnionitis. The vagina and cervix maintain a microenvironment that prevents infections from reaching the uterus. This may be compromised thereby allowing pathogenic bacteria or even an overgrowth of healthy bacterial flora from reaching the placenta. Other risk factors may include poor urogenital hygiene, a short cervix and immunocompromised patients, like in HIV positive mothers.
While hematogenous spread of various pathogenic bacteria is possible, typically hematogenous infections that result in an infected placenta arise due to the TORCH infections :
- Others like syphilis, tuberculosis, listeriosis
- Cytomegalovirus (CMV)
- Herpes simplex virus (HSV)
Symptoms of an Infected Placenta
The clinical presentation can vary with only a few symptoms of low intensity present in some mothers. Diagnosis may therefore be confirmed with follow up blood tests like a complete blood count (raised WBC count) apart from the presence of clinical features. Some of the signs and symptoms of a placental infection includes :
- Abnormal vaginal discharge – may be yellow to green in color with a foul odor
- Abdominal/pelvic tenderness (uterine)
- Rapid heart rate (tachycardia) – mother (> 100 bpm) and/or fetus (>160 bpm)
At other times the symptoms are not typical of an infected placenta and the diagnosis can be missed without further investigation. Although an amniocentesis is avoided as far as possible, it may be necessary for a diagnosis in a subclinical infection.
Treatment of Placental Infection
Broad spectrum IV (intravenous) antibiotics are necessary to prevent maternal and fetal complications. This may be administered before assessing the results of a culture. The antibiotics may be continued by both mother and baby after birth, and the type of antibiotic used on both patients may differ. In acute chorioamnionitis, immediate delivery may be necessary especially if there are signs of fetal distress. However, this is dependent on the stage of pregnancy.