Chorioamnionitis refers to the infection of the innermost layer of cells (a membrane) that covers an embryo or fetus. This is also called intra-amniotic infection. It affects nearly 4% of pregnancies worldwide. It’s also one of the leading causes of pre-term deliveries (1).
This article is pending medical review.
Written by Alessandra Papitto
Reviewed by Sophie Oppelt, Katarzyna Przybył and Carolin Becker
Edited by Juliëtte Gossens
Chorioamnionitis is a common complication during pregnancy. It’s caused by inflammation of parts of the placenta, usually caused by bacterial infections. Because the disease can cause harm both to the pregnant person and the fetus, it can be helpful to know about it.
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What is chorioamnionitis?
What Is Chorioamnionitis?
Chorioamnionitis (pronounced as kor-i-oh-am-ni-on-i-tis) is the inflammation of the membranes lining the embryo or fetus, which are called the chorion and amnion of the placenta. The chorion (outer) and amnion (inner) are the layers that surround the embryo during pregnancy. They are important for nutrient delivery and exchange between the baby and the birthing parent’s body (2).
The inflammation is usually caused by a bacterial infection. These bacteria typically come from the genitals, such as the vagina and the lower cervix. They then travel upward through the cervix towards the uterus. In some cases, the bacteria come from your blood. In other cases still, the infection is caused by invasive prenatal testing. In these tests, a needle is stuck through your belly and into the placenta to take away a bit of tissue or fluid. You can read more about those tests here.
Chorioamnionitis most often happens when your membranes (the chorion and amnion) have ruptured. This is also known as your “water breaking”. When your membranes have ruptured, they are more vulnerable to infection. That’s because there’s now an entrance for bacteria to come through. But chorioamnionitis can develop even with intact membranes.
Everybody carries lots of bacteria with them all the time (our so-called commensal flora). They play an important role in our immune system and our gut health, for example. There are also bacteria in your vagina that help keep it healthy. They are usually harmless, but in some cases they can cause an infection. Over 70% of women carry bacteria in their vagina and cervix that commonly cause chorioamnionitis. But it’s good to know that only a small percentage of people who carry those bacteria will develop chorioamnionitis when they’re pregnant. Scientists are not quite sure why chorioamnionitis develops in some people but not in others (2).
When bacteria cause an infection, your immune system (and that of your baby) respond to that infection. It releases all sorts of small proteins (known as cytokines) to alert the body that there’s an infection. This response can lead to injury or rupture of the membranes (the chorion and amnion) and the cervix. It can also lead to pre-term birth. And sometimes, the infection and your body’s response to it can cause injury and malformation of the fetus (2, 3).
What symptoms you’ll get from chorioamnionitis can vary. This is based on which bacteria caused the infection and how your and your baby’s immune systems respond to them. You can read more about possible symptoms below.
What Are the Risk Factors for Chorioamnionitis?
Chorioamnionitis develops in 1 to 4% of all births. It’s also part of the cause of pre-term birth in 40 to 70% of cases (3). You’re more likely to develop chorioamnionitis if it’s your first pregnancy, or if you’ve had chorioamnionitis in previous pregnancies.
As we already hinted at above, an important risk factor is carrying bacteria in your vagina and cervix that can cause chorioamnionitis. Some people simply carry fewer species of bacteria that lead to infection. And if your normal, healthy vaginal bacteria have been damaged (like when you have a yeast infection), other bacteria might have more chance to cause chorioamnionitis (2, 3).
When you’re already in labor, an important risk factor for developing chorioamnionitis is the length of labor. And more specifically, how long your membranes have been ruptured (which can happen before you go into labor). The more time passes, the higher the risk of infection (3).
Lastly, habits such as smoking and drinking alcohol lead to a higher risk of developing chorioamnionitis.
Diagnosis and Symptoms
As is the case for many infections, one of the main symptoms of chorioamnionitis is getting a fever, usually higher than 38.0 °C (100.4 F). The fever is the first alarm bell from your body, caused by the production of small proteins by your immune system (see above). A fever can help the body fight bacteria and other microbes by making the cells of your immune system more efficient at their job. A fever is the most important sign of chorioamnionitis. If you get a fever, contact your doctor or midwife.
Other common symptoms include a high heart rate (over 100 beats per minute), discharge from your uterus, pain in your belly or pelvis, and amniotic fluid that smells bad (which you can smell if your water breaks).
Your doctor might want to do more testing if they suspect an infection, including monitoring your fetus. If you have chorioamnionitis, the heart rate of your fetus might be increased (over 160 beats per minute).
You might also need to get blood tests done. If you have an infection, you might have a high white blood cell count and your blood sugar (glucose) can also be high. These are all signs that can point your doctor in the right direction for diagnosis.
It's also possible that chorioamnionitis doesn’t cause any of the mentioned symptoms. This means you’re asymptomatic. Instead, you and your doctor may only notice it when you’re going into pre-term labor or if your membranes rupture pre-term (known as pre-term pre-labor rupture of membranes or PPROM) (3, 4).
How Can My Baby Be Affected?
Chorioamnionitis can make you sick. But in 40 to 70% of cases, it can also result in complications for your baby (5-8).
These issues can include:
Pneumonia (an infection of the lungs)
Meningitis (an infection of the membranes covering the brain and spinal cord)
Neurological (brain and nerve) problems
Issues with bone growth
Septic shock (an extreme response to infection)
In the worst cases, chorioamnionitis can cause stillbirth of a baby. Fortunately, this is very rare.
Prevention and Treatment
Prevention is the most important strategy in the fight against chorioamnionitis. This includes making sure to avoid situations in which you’re exposed to poor hygiene as much as possible. This applies especially to sanitation (toilets) and to foods prone to bacterial contamination. Your doctor can tell you which foods are best avoided during pregnancy. Most commonly, this includes foods such as raw dairy or meat products. But which foods are a risk depends on your area.
If your water breaks prematurely, your doctor might give you antibiotics early on to limit the risk of chorioamnionitis (2).
Treatment of chorioamnionitis depends on different factors, such as your age and how healthy you generally are. The best therapy usually includes taking antibiotics. Which antibiotics you need depends on which bacteria or microbes caused your infection. It also depends on where you are in the world, because microbes can be resistant to antibiotics in ways that differ between regions and countries. If you have a high fever, your doctor might also want to give you medication to reduce your fever (2).
Chorioamnionitis is a rare but dangerous pregnancy complication. By avoiding poor hygiene and listening to your health care provider’s advice, you’re already helping to lower your risk. But chorioamnionitis can develop anyway, and it’s not your fault if it does. Make sure to listen to your body and contact your doctor if you get sick or if your water breaks before you expect it to. This way, you can get treated quickly!
Vellamgot AP, Salameh K, Habboub LHM, Pattuvalappil R, Elkabir NA, Siam YS, et al. Suspected clinical chorioamnionitis with peak intrapartum temperature <38°C: the prevalence of confirmed chorioamnionitis and short-term neonatal outcome. BMC Pediatrics. 2022;22(1):197. DOI: 10.1186/s12887-022-03239-9
Tita AT, Andrews WW. Diagnosis and management of clinical chorioamnionitis. Clinics in Perinatology. 2010;37(2):339-54. DOI: 10.1016/j.clp.2010.02.003
Tita ATN. Intraamniotic infection (clinical chorioamnionitis). In: Berghella V, Barss VA (eds.). UpToDate. 2022.
Suzuki S. Association Between Clinical Chorioamnionitis and Histological Funisitis at Term. Journal of Neonatal-Perinatal Medicine. 2019;12(1):37-40. DOI: 10.3233/NPM-17155
Jain VG, Willis KA, Jobe A, Ambalavanan N. Chorioamnionitis and neonatal outcomes. Pediatric Research. 2022;91(2):289-96. DOI: 10.1038/s41390-021-01633-0
Wolfs TG, Jellema RK, Turrisi G, Becucci E, Buonocore G, Kramer BW. Inflammation-induced immune suppression of the fetus: a potential link between chorioamnionitis and postnatal early onset sepsis. The Journal of Maternal-Fetal & Neonatal Medicine. 2012;25(Supplement 1):8-11. DOI: 10.3109/14767058.2012.664447
Galinsky R, Polglase GR, Hooper SB, Black MJ, Moss TJ. The consequences of chorioamnionitis: preterm birth and effects on development. Journal of Pregnancy. 2013;2013:412831. DOI: 10.1155/2013/412831
Williams MC, O’Brien WF, Nelson RN, Spellacy WN. Histologic chorioamnionitis is associated with fetal growth restriction in term and preterm infants. American Journal of Obstetrics and Gynecology. 2000;183(5):1094-9. DOI: 10.1067/mob.2000.108866
Please note: the information we provide to you here is for educational purposes only. If you’re experiencing any discomfort or have any complaints or questions about your health, please contact your doctor or other relevant health professional. We don’t provide medical advice.