Clinical significance of the presence of amniotic fluid 'sludge' in asymptomatic patients at high risk for spontaneous preterm delivery

Abstract

Objectives: To determine the clinical significance of the presence of amniotic fluid (AF) 'sludge' among asymptomatic patients at high risk for spontaneous preterm delivery.

Methods: This retrospective case-control study included 281 patients with (n = 66) or without (n = 215) AF 'sludge', who underwent transvaginal ultrasound examination between 13 and 29 completed weeks of gestation. Patients with threatened preterm labor, multiple gestation, fetal anomalies, placenta previa or uterine contractions were excluded.

Results: The prevalence of AF 'sludge' in the study population was 23.5% (66/281). The rates of spontaneous preterm delivery at < 28 weeks, < 32 weeks, < 35 weeks and < 37 weeks of gestation were 14.7% (29/197), 21.3% (46/216), 28.7% (62/216) and 42.1% (91/216), respectively. Patients with 'sludge' had: (1) a higher rate of spontaneous preterm delivery at < 28 weeks (46.5% (20/43) vs. 5.8% (9/154); P < 0.001), < 32 weeks (55.6% (25/45) vs. 12.3% (21/171); P < 0.001) and < 35 weeks (62.2% (28/45) vs. 19.9% (34/171); P < 0.001); (2) a higher frequency of clinical chorioamnionitis (15.2% (10/66) vs. 5.1% (11/215); P = 0.007), histologic chorioamnionitis (61.5% (40/65) vs. 28% (54/193); P < 0.001) and funisitis (32.3% (21/65) vs. 19.2% (37/193); P = 0.03); (3) a higher frequency of preterm prelabor rupture of membranes (PROM) (39.4% (26/66) vs. 13.5% (29/215); P < 0.001), lower gestational age at preterm PROM (median 24.7 (interquartile range (IQR), 22.3-28.1) weeks vs. 32.3 (IQR, 27.7-34.8) weeks; P < 0.001); and (4) shorter median ultrasound-to-delivery interval ('sludge' positive 127 days (95% CI, 120-134 days) vs. 'sludge' negative 161 days (95% CI, 153-169 days); P < 0.001) and ultrasound-to-preterm PROM interval ('sludge' positive 23 days (95% CI, 7-39 days) vs. 'sludge' negative 57 days (95% CI, 38-77 days); P = 0.003) than those without 'sludge'. AF 'sludge' was an independent explanatory variable for the occurrence of spontaneous preterm delivery at < 28 weeks, < 32 weeks and < 35 weeks, preterm PROM, microbial invasion of the amniotic cavity (MIAC) and histologic chorioamnionitis. Moreover, the combination of a cervical length < 25 mm and 'sludge' conferred an odds ratio of 14.8 and 9.9 for spontaneous preterm delivery at < 28 weeks and < 32 weeks, respectively.

Conclusions: AF 'sludge' is an independent risk factor for spontaneous preterm delivery, preterm PROM, MIAC and histologic chorioamnionitis in asymptomatic patients at high risk for spontaneous preterm delivery. Furthermore, the combination of 'sludge' and a short cervix confers a higher risk for spontaneous preterm delivery at < 28 weeks and < 32 weeks than a short cervix alone.

Figure 1

A) Transvaginal ultrasound image showing the presence of dense aggregates of particulate matter (amniotic fluid ‘sludge’) in the proximity of the internal cervical os; B) Similar image showing a slight detachment of the fetal membranes (white arrows) at the level of the internal cervical os. The ‘sludge’ contour is well defined, confirming that ‘sludge’ is located in the amniotic cavity.

Figure 2

Frequency of spontaneous preterm delivery at <28 weeks of gestation according to cervical length and the presence or absence of AF ‘sludge’: [<15 mm: ‘sludge’ (+) 53.8% vs. ‘sludge’ (-) 12.1%; p=0.001]; [15-25 mm: ‘sludge’ (+) 27.3% vs. ‘sludge’ (-) 2.3%; p=0.02]; and [>25 mm: ‘sludge’ (+) 37.5% vs. ‘sludge’ (-) 4.3%; p<0.001].

Figure 3

Frequency of spontaneous preterm delivery at <32 weeks of gestation according to cervical length and the presence or absence of AF ‘sludge’: [<15 mm: ‘sludge’ (+) 69.2% vs. ‘sludge’ (-) 24.2%; p<0.001]; [15-25 mm: ‘sludge’ (+) 36.4% vs. ‘sludge’ (-) 13.6%; p=0.1]; and [>25 mm: ‘sludge’ (+) 37.5% vs. ‘sludge’ (-) 7.4%; p=0.006].

Figure 4

Kaplan-Meier survival analysis of the ultrasound-to-delivery interval (days) according to the presence or absence of AF ‘sludge’ in asymptomatic high-risk patients for preterm delivery. Patients with ‘sludge’ (dotted line) had a shorter ultrasound-to-delivery interval than those without AF ‘sludge’ (solid line). [AF ‘sludge’ positive, median: 127 (95% CI: 120-134) days vs. AF ‘sludge’ negative, median: 161 (95% CI: 153-169) days; log rank test, p<0.001].