Severe Polyhydramnios

Severe polyhydramnios is amniotic fluid with an index of 35 cm or more or a deepest vertical pocket of 16 cm or more. It is often symptomatic and is most associated with fetal anomalies (gastrointestinal obstruction, neurological disease, skeletal dysplasia), twin to twin transfusion, poorly controlled maternal diabetes and fetal anaemia. It matters because it carries the highest risk of preterm labour, cord prolapse, abruption and perinatal death.

• Risk factors: uncontrolled diabetes, monochorionic twins, fetal anomaly, alloimmunisation, parvovirus.
• Rapid increase over days suggests twin to twin transfusion or infection.

Women have a very tense abdomen, marked breathlessness, discomfort, difficulty lying flat, oedema of the legs and vulva, and reduced urine in extreme cases. Fetal parts cannot be felt and heart sounds are hard to hear.

• Fundal height more than 6 cm above dates.
• Shiny skin with striae.
• Differential diagnosis: ascites, ovarian cyst, large multiple pregnancy, macrosomia, moderate polyhydramnios, hydatidiform mole.
• Complications: preterm labour, premature rupture of membranes with cord prolapse, placental abruption, malpresentation, postpartum haemorrhage, maternal respiratory compromise, venous thrombosis, fetal death.

The approach is a detailed scan with extensive tests for the cause.

• Ultrasound: amniotic fluid index 35 cm or more or deepest vertical pocket 16 cm or more; anomaly scan, stomach bubble, swallowing, kidneys, spine, skull, chest, limbs, fetal movements; twin chorionicity and bladder sizes; fetal weight.
• 75 g oral glucose tolerance test and HbA1c; maternal blood group and antibody screen, syphilis, TORCH serology, parvovirus B19; middle cerebral artery peak systolic velocity.
• Amniocentesis for karyotype, microarray and infection PCR.
• Cervical length scan for the risk of preterm birth; fetal echocardiography.

The principle is to treat the cause, relieve symptoms by amnioreduction when needed and plan delivery in a unit with neonatal intensive care.

• Supportive: admit if symptomatic; rest in a semi sitting position; oxygen if saturation is below 94 percent; compression stockings for oedema; daily fetal movement counts; deliver in a facility with theatre and neonatal intensive care.
• Pharmacological: indomethacin 25 mg oral 6-hourly for no more than 48 hours before 32 weeks, with repeat scan of the ductus arteriosus and fluid; diabetes: isophane insulin 0.2 units/kg subcutaneous at bedtime plus soluble insulin 4 to 6 units subcutaneous before meals, adjusted by 2 units every 3 days, with metformin 500 mg oral with meals to 1 g 12-hourly (maximum 2.5 g daily); betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days; nifedipine 20 mg oral once then 10 to 20 mg every 6 to 8 hours for up to 48 hours for threatened preterm labour; enoxaparin 40 mg subcutaneous daily during admission; oxytocin 10 IU IM at birth and infusion of 20 IU in 1 litre sodium chloride 0.9 percent at 125 mL per hour for 4 hours.
• Procedures: amnioreduction of up to 2 to 3 litres, no faster than 1 litre per 20 minutes, with an 18 gauge needle under ultrasound, repeated as needed; intrauterine transfusion for fetal anaemia; laser coagulation of placental vessels for twin to twin transfusion; delivery at 37 to 38 weeks, earlier for contractions or fetal compromise; controlled amniotomy with the presenting part held.
• Special groups: women with diabetes need hourly glucose in labour with insulin infusion of 1 to 2 units per hour for glucose above 7 mmol/L; newborns have a nasogastric tube passed to exclude oesophageal atresia and glucose checked at 2 hours.
• Red flags: contractions, rupture of membranes, breathlessness at rest, abdominal pain, vaginal bleeding, reduced fetal movements.
• Follow-up: amniotic fluid index weekly; cervical length every 2 weeks; growth scans every 2 to 4 weeks; newborn examination and paediatric review.