Press release - Published on 9.11.2026 09.49 # Placental inflammation may increase the fetal brain's vulnerability to oxygen deprivation during labor During labor, the risk of fetal oxygen deprivation is assessed largely using cardiotocography (CTG) monitoring. CTG is the most widely used method worldwide for monitoring fetal wellbeing during labor, but its interpretation remains challenging. Similar changes in the fetal heart rate do not necessarily indicate the same level of risk for every fetus.  In a study conducted by HUS researcher and midwife Mikko Tarvonen, fetuses exposed to inflammation showed fewer of the pro-nounced heart rate decelerations that are typically associated with oxygen deprivation in CTG monitoring than other fetuses. An international study led by researchers from HUS and University of Helsinki found that chorioamniotis, an inflammation of the placenta and fetal membranes, may both lower the fetal tolerance to oxygen deprivation and obscure the heart rate changes commonly used to recognize the risk. The study investigated how intrauterine inflammation affects the way full-term fetuses respond to oxygen deprivation during labor and how much oxygen deprivation is needed for brain injury to develop. ## Greater risk, subtler warning signs “Our most important finding was that fetuses exposed to inflammation showed fewer of the pronounced heart rate decelerations that are typically associated with oxygen deprivation in CTG monitoring than other fetuses. At the same time, their risk of oxygen deprivation-related risk of brain injury was higher,” says the corresponding author of the study, Midwife **Mikko Tarvonen** from HUS. Fetuses exposed to chorioamniotis may have developed brain injury following less severe oxygen deprivation when compared to babies who were not exposed to chorioamniotis. This finding is significant because, according to the study, similar changes in the CTG may not indicate the same level of risk for all fetuses. ## Large study based on data from more than 3,000 newborns The study analyzed data from 3,487 newborns. The researchers report that this is the largest pulished cohort of newborns diagnosed at birth with umbilical artery acidemia, meaning acidic pH of blood. The risk of chorioamniotis increases particularly when there is a prolonged period of time between the rupture of the membranes (water breaking) and delivery, which may allow bacteria to ascend from the birth canal into the uterus. Chorioamniotis was identified in 569 deliveries, which is 16,3 percent of the cases included in the study. In this study, chorioamnionitis was associated with a 4.6-fold increased risk of oxygen deprivation-related brain injury. ## Inflammation may reduce fetal tolerance to oxygen deprivation According to the study, the findings do not suggest that inflammation alone causes brain injury. Rather, inflammation may reduce the fetus’s tolerance to oxygen deprivation, allowing neurological damage to occur with less severe oxygen deprivation than in fetuses not exposed to inflammation. The researchers describe this as a “two-hit” model. “It appears that inflammation and oxygen deprivation may be more dangerous together than either of them alone. In a way, inflammation lowers the threshold at which oxygen deprivation can cause brain injury,” Tarvonen explains. ## Results provide new information for professionals managing deliveries First and foremost, the results of the study provide new information for the professionals who manage labor and delivery. “The results of the study do not mean that every child exposed to intrauterine inflammation will develop brain damage. Even though inflammation increases the risk, brain injury remains rare and does not occur in the majority of exposed infants. It is also not possible to predict a single fetus’s risk based on just fever or a single CTG finding,” Tarvonen states. According to the researchers, the findings may help develop more individualized fetal monitoring methods to be used during delivery. The aim is to interpret the CTG as part of a broader clinical picture, taking into account maternal, fetal and labor-related factors. Research article: [Clinical and histological chorioamnionitis, particularly when associated with funisitis, attenuate intrapartum fetal heart rate responses and increase vulnerability to hypoxic-ischemic brain injury at milder degrees of acidemia](https://www.ajog.org/article/S0002-9378(26)00412-6/fulltext "Clinical and histological chorioamnionitis, particularly when associated with funisitis, attenuate intrapartum fetal heart rate responses and increase vulnerability to hypoxic-ischemic brain injury at milder degrees of acidemia") *In university hospitals research is part of treatment: new research outcomes make treatment practises more efficient and help focus treatments correctly. 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