How common is chorioamnionitis in the US?

Updated: May 08, 2018
  • Author: Fayez M Bany-Mohammed, MD; Chief Editor: Ted Rosenkrantz, MD  more...
  • Print

The prevalence of maternal chorioamnionitis in the United States varies with different publications, but it appears to be inversely correlated with gestational age at birth. In a 2014 study that assessed the entire US population and linked infant birth and death certificate files for the year 2008, the prevalence of chorioamnionitis was 9.7 per 1000 live births. [69] Studies that looked at placentas found histologic chorioamnionitis present in 3%-5% of term placentas and in 94% of placentas delivered at 21-24 weeks of gestation. [31]

The risk of chorioamnionitis increases based on health conditions and behaviors, as outlined in the Pathophysiology section. Furthermore, factors such as gestational age, economic conditions, and ethnic differences influence the incidence. Histopathology of the placenta suggests inflammation may occur in the normal course of parturition at term gestation, thus complicating the definition of chorioamnionitis. An increase in histopathologic chorioamnionitis is noted in cases of preterm birth as compared with delivery of the healthy term infant. Signs of placental inflammation are present in 42% of extremely low birth weight infants. [70] Most investigators agree that infection is directly or indirectly associated with 40%-60% of all preterm births. [71]

Infants exposed to maternal acute chorioamnionitis are at increased risk for early-onset sepsis (EOS). The risk is modified by gestational age and maternal treatment with intrapartum antibiotics. Data from the 1980s and 1990s showed that asymptomatic infants born at term gestation to mothers who received intrapartum treatment for clinical chorioamnionitis have a 1.5% incidence rate of positive blood cultures, whereas symptomatic term infants with chorioamnionitis born to mothers who received intrapartum treatment have a 13% incidence rate of positive cultures 13%. [72]

More recent reports continue to indicate that the risk of EOS in infants born to women with chorioamnionitis remains strongly dependent on gestational age, but this risk is much lower compared to old data. In three reports including 1892 infants born at 35 weeks or more of gestation to mothers with clinical chorioamnionitis, [73, 74, 75] the rates of EOS (positive blood culture at 4</ref> [76]  None of these studies stratified risk according to presence or absence of clinical signs of illness; however, more recent data from the National Institute of Child Health and Human Development (NICHD) Neonatal Research Network suggest the risk to be very low in asymptomatic late preterm and term neonates. [77]

Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!