Amniotic Fluid Sludge

Amniotic fluid sludge is echogenic particulate matter lying near the internal cervical os in the amniotic fluid, found on transvaginal ultrasound in the second trimester. It is made of cells, vernix and inflammatory debris and is linked to microbial invasion of the amniotic cavity and sterile intra-amniotic inflammation. It matters because it predicts preterm birth, membrane rupture and chorioamnionitis, especially with a short cervix.

• Risk factors: short cervix, previous preterm birth, bleeding, genital infection, smoking.
• Sludge with a short cervix greatly raises the chance of birth before 34 weeks.
• It does not always mean infection, but infection must be excluded.

Women usually have no symptoms. Some have pelvic pressure, watery discharge or contractions, and examination may be normal.

• Found at the cervical length scan or anomaly scan.
• Often accompanies a short or funnelled cervix.
• Differential diagnosis: vernix or blood clot in the fluid, meconium, amnionitis, cervical funnelling, normal particulate matter after amniocentesis.
• Complications: preterm labour, preterm rupture of membranes, chorioamnionitis, neonatal sepsis, extremely preterm birth, pregnancy loss.

The approach is transvaginal ultrasound with infection assessment.

• Transvaginal ultrasound: dense echogenic aggregates in the fluid near the internal os, cervical length, funnelling, amniotic fluid index; repeated every 1 to 2 weeks.
• Maternal temperature, pulse, uterine tenderness; full blood count and C-reactive protein; high vaginal and rectovaginal swab; urine culture.
• Amniocentesis in specialist units for glucose below 1.1 mmol/L, white cell count, Gram stain and culture, to exclude intra-amniotic infection.
• Screen for bacterial vaginosis, chlamydia, gonorrhoea, syphilis and HIV.

The principle is to treat infection if found, to support the cervix when short and to prepare for preterm birth.

• Supportive: pelvic rest; stop smoking; avoid heavy lifting; teach the symptoms of preterm labour and leaking fluid; antenatal review every 2 weeks; birth in a facility with neonatal intensive care when below 34 weeks.
• Pharmacological: micronised progesterone 200 mg vaginal at night from diagnosis to 36 weeks for a cervical length below 25 mm; metronidazole 400 mg oral 12-hourly for 7 days for bacterial vaginosis; for confirmed intra-amniotic infection give ampicillin 2 g IV 6-hourly plus gentamicin 5 mg/kg IV once daily plus azithromycin 500 mg IV or oral daily, and deliver; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if delivery is likely; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks; nifedipine 20 mg oral once then 10 to 20 mg every 6 to 8 hours for up to 48 hours for contractions without infection.
• Procedures: McDonald cervical cerclage at 16 to 24 weeks for a cervical length below 25 mm with a previous preterm birth, with sludge but no infection or bleeding; removal at 36 to 37 weeks, or at once for infection, rupture or labour; no cerclage if infection is confirmed.
• Special groups: women with confirmed intra-amniotic infection are delivered at any gestation after antibiotics start; women with HIV continue tenofovir 300 mg, lamivudine 300 mg and dolutegravir 50 mg oral once daily.
• Red flags: fever, uterine tenderness, foul discharge, contractions, leaking fluid, bleeding, fetal tachycardia.
• Follow-up: cervical length and sludge scan every 1 to 2 weeks to 28 weeks; full blood count and C-reactive protein if symptoms; antenatal review every 2 weeks; neonatal team informed of the risk.