High- but not low-grade histologic chorioamnionitis is associated with spontaneous preterm birth in a Swedish cohort

<b>Objective:</b> To examine whether different grades of placenta inflammation are associated with risk for spontaneous preterm birth, taking into consideration maternal and delivery factors. Placentas from spontaneous preterm births were compared with a control group from full-term deliveries. <b>Methods:</b> Placentas from 98 full-term, 71 late preterm (gestational week 34–37), and 65 early preterm (gestational week 22–33) singleton deliveries were analysed from the Karolinska University Hospital in Stockholm. The placentas were examined for histologic chorioamnionitis (HCA) grade 1 (low) and 2 (high). Mother, child, and delivery parameters were collected from maternity centre and delivery forms. <b>Results:</b> There was a relatively low incidence of HCA in the preterm groups (26.7% and 38.5% in the late and early preterm groups, respectively). HCA 2 was most common in the early preterm group and HCA 1 was most common in the full-term group. The odds of early preterm birth was <i>lower</i> for placentas with HCA 1 compared to HCA 2 (OR = 0.17) and higher for placentas with HCA 2 compared to no HCA (OR = 2.17). <b>Conclusions:</b> Despite a relatively low incidence of HCA in the preterm groups, HCA 2 seems to be associated with early preterm birth whereas HCA 1 seems to be part of the full-term delivery.