Amniotic fluid sludge is associated with earlier preterm delivery and raised cervicovaginal interleukin 8 concentrations

Abstract

Preterm birth is the leading cause of global neonatal mortality. Amniotic fluid sludge, thought to indicate intra-amniotic infection, may have potential as a clinical biomarker of preterm birth risk. This study aimed to analyse whether the presence of amniotic fluid sludge in pregnant participants with a known short cervical length, can help improve understanding of aetiology and guide management choice. A retrospective cohort study analysing the effects of amniotic fluid sludge presence on risk of preterm birth in high-risk asymptomatic pregnant participants with a short cervical length (<25 mm) at a large tertiary referral maternity centre in London. Amniotic fluid sludge was detected on routine transvaginal ultrasound scan. 147 pregnant participants with short cervical length were identified, 54 of whom had amniotic fluid sludge. Pregnant participants with amniotic fluid sludge were more likely to have a short cervical length (14 vs 19 mm, p <0.0001), and increased cervicovaginal fetal fibronectin concentrations at diagnosis, compared to pregnant participants without AFS (125 vs 45 ng/mL, p=0.0006). Pregnant participants with amniotic fluid sludge were at increased risk of mid trimester loss and delivery before 24 gestational weeks (RR 3.4 [1.2-10.3]). Furthermore, we showed that pregnant participants with amniotic fluid sludge have increased cervicovaginal interleukin 8 concentrations supporting the concept of amniotic fluid sludge as an indicator of an inflammatory response to microbial invasion (p=0.03). Neonatal outcomes were similar between the two groups. In our cohort of high-risk asymptomatic pregnant participants with a short cervical length, the presence of amniotic fluid sludge is associated with increased risk of delivery before 24 weeks gestation. Pregnant participants with amniotic fluid sludge were also more likely to have raised fetal fibronectin levels and inflammatory cytokines, particularly interleukin 8, in the cervicovaginal fluid supporting the concept that AFS is associated with an infective or inflammatory process. Future research should aim to further establish the clinical significance of amniotic fluid sludge presence and guide subsequent management.