Chorioamnionitis

Chorioamnionitis (also called intraamniotic infection) is a serious type of infection that can occur during pregnancy when bacteria from the mother’s body travel up the birth canal and infect the fetal membranes and/or amniotic fluid. The infection typically originates from bacteria in the mother’s vagina which migrate upward towards the uterus. It is not a common event as only 2% of all pregnancies in the U.S. are affected by chorioamnionitis. Chorioamnionitis can pose a very serious threat to the health of baby because the infection in the fetal membranes will significantly disrupt the supply of nutrients and oxygen from mother to baby. Moreover, when left undiagnosed and untreated for too long a chorioamnionitis infection can actually be transferred to the baby which can cause serious brain damage. In addition to these risks, chorioamnionitis can also trigger premature delivery which comes with its own host of health risks for the baby.

What Causes Chorioamnionitis?

Chorioamnionitis is just like most other infections in that it is caused by unhealthy invading and growing within the body. The bacteria that causes chorioamnionitis is usually a common type of polymicrobial bacteria that originates in the colon or vagina of the pregnant mother. Bacteria such as ureaplasma and mycoplasma hominis are commonly found in the lower genital tract of most women. From there the bacteria grows, spreads and eventually migrates up through the birth canal in the direction of the uterus. Once the bacteria spreads to the uterus it quickly finds an environment for bacterial growth in the membranes and chorion of the placenta. The risk of a chorioamnionitis infection drastically increases when the fetal membranes / amniotic sac rupture prematurely or a long time before the baby is actually delivered. A history of urinary tract infections increases the risk of chorioamnionitis. Women who have what is known as a “short cervix” (i.e., a short distance between the cervix and uterus) are also at increased risk.

Diagnosing Chorioamnionitis

A diagnosis of chorioamnionitis is typically based entirely on clinical signs and findings. This is because taking a sample of the membrane or amniotic fluid for testing is simply not safe or practical under most circumstances. When time and circumstances permit, however, a sample of amniotic fluid can be extracted for testing using a ultrasound guided needle aspiration technique. The vast majority of chorioamnionitis cases get diagnosed based on clinical findings alone. The most important clinical symptom of chorioamnionitis is persistent maternal fever. The 2 measurable clinical symptoms used to diagnose chorioamnionitis are:

• Maternal Fever: low-grade fevers (below 101° F) during pregnancy are not uncommon, particularly during labor. However, a persistent low-grade fever or any fever over 101° F is a strong clinical sign of a potential infection. Fever is a documented clinical symptom in almost 100% of all chorioamnionitis cases. In fact, fever is usually required as a prerequisite to diagnosis.
• Tachycardia: maternal and fetal tachycardia (fast heart beat) are the second most common symptom of chorioamnionitis. For diagnostic purposes, maternal tachycardia is defined as a heart rate over 100 BPM and fetal tachycardia is anything over 160 BPM. Maternal tachycardia is reported in 60-80% of all chorioamnionitis cases and fetal tachycardia is report in 50-70% of cases. Tachycardia can be caused by a number of other things aside from infection. However, when the symptoms of maternal fever and tachycardia appear together they are considered a very strong indicator of chorioamnionitis.

There are 2 other, highly subjective clinical symptoms often used to help reach a diagnosis of chorioamnionitis: (1) fundal tenderness; and (2) a bad odor in the vagina or amniotic fluid. The main problem with uterine fundal tenderness is that it can be almost impossible to assess during labor. The mother is usually either in too much general pain and discomfort or numb from an epidural injection, both of which effectively mask any fundal tenderness. Foul odor is usually only present in cases where the infection has persisted for very long time. These 2 secondary symptoms of chorioamnionitis are only reported in about 25% of all cases.

Treatment of Chorioamnionitis

Chorioamnionitis can be very dangerous to the health of the baby, but if it is promptly diagnosed it can be effectively treated. Treatment for chorioamnionitis involves immediate and aggressive antibiotic therapy. Various studies have demonstrated that the prompt use of broad-spectrum antibiotics will drastically reduce the risks of harm to both baby and mother from a chorioamnionitis infection. Antibiotics will reduce the risk of neonatal sepsis by more than 80% when administered early on. The most commonly used antibiotic for treating chorioamnionitis ampicillin, which is typically given intravenously every 4-6 hours during labor and then a single dose following delivery.