Oligohydramnios Due to Membrane Rupture

Oligohydramnios due to membrane rupture is reduced amniotic fluid caused by leakage through ruptured membranes, whether at term or preterm. It is the commonest cause of oligohydramnios in the second and third trimesters. It matters because infection, cord compression, abruption and, with rupture before 24 weeks, pulmonary hypoplasia can follow, and the gestation decides management.

• Risk factors: previous preterm rupture, smoking, genital infection, cervical surgery, multiple pregnancy, polyhydramnios, antepartum bleeding.
• Latency to labour is longer at earlier gestation.
• Preterm rupture is a leading cause of preterm birth.

Women report a gush or continuous trickle of clear fluid, with wet underwear and no contractions at first. Fundal height may be small and the fetus easily felt.

• Fluid pooling in the posterior fornix on speculum examination.
• Fever, uterine tenderness and fetal tachycardia mean infection.
• Differential diagnosis: urinary incontinence, vaginal discharge, mucus plug show, cervicitis, bacterial vaginosis, urine leakage from a fistula.
• Complications: chorioamnionitis, cord prolapse, placental abruption, preterm labour, pulmonary hypoplasia, limb contracture, neonatal sepsis, stillbirth.

The approach is to confirm rupture and measure fluid, and to exclude infection and labour.

• Sterile speculum examination: pooling of fluid, fluid on coughing, nitrazine paper turning blue (pH above 6.5), ferning on microscopy.
• Placental alpha microglobulin 1 or insulin-like growth factor binding protein 1 test on vaginal fluid where available.
• Ultrasound: amniotic fluid index, deepest vertical pocket, fetal weight, presentation, cord position; cardiotocography; avoid digital examination unless in labour.
• Maternal temperature, pulse, full blood count, C-reactive protein; high vaginal and rectovaginal swab for group B streptococcus.

The principle is antibiotics, steroids for preterm rupture and delivery at 34 weeks or at term, with early treatment of infection.

• Supportive: admit; no vaginal examinations; sanitary pad changed and checked 4-hourly; temperature 4-hourly; daily fetal movement counts; oral water 2 to 3 litres daily.
• Pharmacological:
  • Amoxicillin 500 mg oral 8-hourly plus erythromycin 250 mg oral 6-hourly for 7 days for rupture before 37 weeks (avoid amoxicillin-clavulanate).
  • Betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days.
  • Magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks.
  • Benzylpenicillin 5 million units IV then 2.5 million units 4-hourly during labour for group B streptococcus or rupture for 18 hours or more at term.
  • Ampicillin 2 g IV 6-hourly plus gentamicin 5 mg/kg IV once daily for chorioamnionitis.
  • Oxytocin 10 IU IM at birth.
• Procedures: expectant care to 34 weeks in the absence of infection, abruption or fetal compromise; induction or caesarean section at 34 weeks and at once for infection, abruption or abnormal tracing; induction at term with misoprostol 25 micrograms vaginal 6-hourly (maximum 4 doses) or oxytocin; amnioinfusion in labour for variable decelerations.
• Special groups: previable rupture before 24 weeks carries a risk of pulmonary hypoplasia, and counselling about expectant care or termination is needed; penicillin allergy with a severe reaction uses clindamycin 900 mg IV 8-hourly.
• Red flags: temperature above 38 degrees Celsius, foul-smelling liquor, uterine tenderness, fetal tachycardia above 160 beats per minute, bleeding, cord prolapse, contractions.
• Follow-up: inpatient monitoring with white cell count and C-reactive protein every 2 days; amniotic fluid index weekly; newborn sepsis check; postnatal review at 6 weeks.