The prevalence and clinical significance of amniotic fluid 'sludge' in patients with preterm labor and intact membranes

Objective: To determine the prevalence and clinical significance of amniotic fluid (AF) 'sludge' observed during transvaginal ultrasound examination of the cervix in patients with preterm labor and intact membranes, and in those with uncomplicated pregnancies. Methods: This retrospective study included patients with preterm labor and intact membranes (h = 84) and those with uncomplicated term pregnancies (n = 298). The outcome variables included the occurrence of documented microbial invasion of the amniotic cavity (MIAC), histological chorioamnionitis, examination-to-delivery interval, admission to the neonatal intensive care unit (NICU), a composite neonatal morbidity, perinatal death, and delivery within 48 h, 7 days, and < 35 weeks and < 32 weeks. Statistical analysis included Chi-square test, stepwise logistic regression analysis and survival analysis. Results: The prevalence of AF 'sludge' was 1% (3/298) in patients with uncomplicated term pregnancies and 22.6% (19/84) in those with preterm labor and intact membranes. Among patients with preterm labor and intact membranes: (1) cervical length ≤ 15 mm was present in 58.3% (49/84) of the patients; (2) the prevalence of MIAC and histological chorioamnionitis was 12.1% (7/58) and 32.9% (25/76), respectively; (3) the rate of spontaneous preterm delivery within 48 h, 7 days, and < 32 weeks and < 35 weeks of gestation was 13.6% (8/59), 28.8% (17/59), 39.5% (17/43) and 50.8% (30/59), respectively; (4) patients with AF 'sludge' had a higher frequency of positive AF cultures [33.3% (6/18) vs. 2.5% (1/40), P = 0.003] and histological chorioamnionitis [77.8% (14/18) vs. 19% (11/58), P < 0.001] than those without AF 'sludge'; (5) a higher proportion of neonates born to patients with AF 'sludge' was admitted to the NICU [64.3% (9/14) vs. 12.9% (8/62), P < 0.01], had a composite neonatal morbidity [36.8% (7/19) vs. 13.8% (9/65), P = 0.04] and died in the perinatal period [36.8% (7/19) vs. 4.6% (3/65), P = 0.001] than those born to women without 'sludge'; (6) a higher proportion of patients with AF 'sludge' had spontaneous delivery within 48 h [42.9% (6/14) vs. 4.4% (2/45), P = 0.001], within 7 days [71.4% (10/14) vs. 15.6% (7/45), P < 0.001], < 32 weeks [75% (9/12) vs. 25.8% (8/31), P = 0.005] and < 35 weeks [92.9% (13/14) vs. 37.8% (17/45), P < 0.001] than those without AF 'sludge'; and (7) patients with AF 'sludge' had a shorter examination-to-delivery interval than those without AF 'sludge' [AF 'sludge' median, 1 (IQR, 1-5) days vs. no AF 'sludge' median, 33 (IQR, 18-58) days; P < 0.001]. Conclusion: The presence of AF 'sludge' in patients with preterm labor and intact membranes is a risk factor for MIAC, histological chorioamnionitis and impending preterm delivery.