Moderate Polyhydramnios

Moderate polyhydramnios is excess amniotic fluid with an amniotic fluid index of 30 to 34.9 cm or a deepest vertical pocket of 12 to 15.9 cm. Causes include maternal diabetes, fetal swallowing disorders (oesophageal atresia, neurological disease), fetal anaemia, infection, chromosomal abnormality and twin to twin transfusion recipient. It matters because fetal anomalies are found in a considerable proportion, and symptoms of preterm labour and breathlessness are more frequent.

• Risk factors: diabetes, multiple pregnancy, fetal anomaly, alloimmunisation, parvovirus, cytomegalovirus.
• The proportion with a cause rises with severity.
• Many have a normal outcome after a full work up.

Women have a tense, large abdomen for dates, discomfort, breathlessness and sometimes oedema of the legs and vulva. Fetal parts are hard to feel and the heart sounds are distant.

• Fundal height more than 3 cm above dates.
• Difficulty in palpating the fetus.
• Differential diagnosis: macrosomia, multiple pregnancy, wrong dates, ascites, diabetes related polyhydramnios, fetal gastrointestinal obstruction, fetal anaemia, idiopathic polyhydramnios.
• Complications: preterm labour, premature rupture of membranes, malpresentation, cord prolapse, placental abruption on rupture, postpartum haemorrhage, maternal respiratory compromise.

The approach is a full scan and tests for the common causes.

• Ultrasound: amniotic fluid index 30 to 34.9 cm or deepest vertical pocket 12 to 15.9 cm; detailed anomaly scan with stomach bubble, swallowing, bowel loops, skull, spine, chest, kidneys; growth and abdominal circumference.
• 75 g oral glucose tolerance test; HbA1c if already known diabetes.
• Maternal blood group and antibody screen, syphilis, TORCH serology, parvovirus B19; middle cerebral artery peak systolic velocity.
• Amniocentesis for karyotype, microarray and infection PCR when anomalies, growth restriction or severe disease are present; fetal echocardiography.

The principle is to treat the cause, to relieve symptoms and to plan delivery at 38 to 39 weeks.

• Supportive: rest; avoid heavy work; semi sitting position for breathlessness; teach to report contractions, leaking fluid and reduced movements; deliver in a facility with caesarean section and neonatal care.
• Pharmacological: diabetes: metformin 500 mg oral with meals increased to 1 g 12-hourly (maximum 2.5 g daily) and 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; indomethacin 25 mg oral 6-hourly for no more than 48 hours before 32 weeks for symptomatic disease, with repeat ultrasound of the ductus arteriosus; benzathine benzylpenicillin 2.4 million units IM once weekly for 3 weeks for syphilis; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if delivery is likely; 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 to prevent bleeding.
• Procedures: amnioreduction of up to 2 litres, no faster than 1 litre per 20 minutes, for tense symptomatic disease; induction at 38 to 39 weeks with controlled amniotomy; intrauterine transfusion for fetal anaemia; caesarean section for obstetric reasons.
• 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 glucose checked at 2 hours, with glucose below 2.6 mmol/L treated by dextrose 10 percent 2 mL/kg IV over 10 minutes then 80 mL/kg per day, and a nasogastric tube is passed to exclude oesophageal atresia.
• Red flags: contractions, rupture of membranes, abdominal pain, breathlessness, vaginal bleeding after rupture, reduced fetal movements.
• Follow-up: amniotic fluid index every 2 weeks; growth scans every 4 weeks; newborn examination for anomalies.