Mild Polyhydramnios

Mild polyhydramnios is excess amniotic fluid with an amniotic fluid index of 24 to 29.9 cm or a deepest vertical pocket of 8 to 11 cm. It is the most frequent degree, and most cases are idiopathic or related to mild maternal hyperglycaemia. It matters because outcomes are usually good, but diabetes and fetal anomalies must still be excluded.

• Risk factors: diabetes, multiple pregnancy, fetal anomaly, maternal obesity, red cell alloimmunisation.
• Rarely causes symptoms.

Women are usually well, and the fundal height may be 2 to 3 cm above dates. Some report mild discomfort or breathlessness.

• Fundal height larger than dates.
• Fetal parts easily palpable.
• Differential diagnosis: wrong dates, macrosomia, multiple pregnancy, maternal diabetes, fetal anomaly, fetal anaemia, normal variation.
• Complications: preterm labour, malpresentation, cord prolapse on rupture, abruption, postpartum haemorrhage, progression to moderate disease.

The approach is ultrasound with a search for diabetes and fetal anomaly.

• Ultrasound: amniotic fluid index 24 to 29.9 cm or deepest vertical pocket 8 to 11 cm, plus a detailed anomaly scan (stomach bubble, swallowing, spine, face, chest, kidneys, limbs), fetal growth.
• 75 g oral glucose tolerance test: fasting 5.1 mmol/L or more, 1 hour 10.0 mmol/L or more, 2 hours 8.5 mmol/L or more.
• Maternal blood group and antibody screen, syphilis test, TORCH serology and parvovirus B19 if indicated.
• Middle cerebral artery peak systolic velocity if anaemia is suspected; amniocentesis for karyotype if anomalies are found.

The principle is to treat diabetes if present and to observe, with delivery at 39 weeks for idiopathic disease.

• Supportive: rest; avoid overstretching activity; counselling about preterm labour symptoms; delivery in a facility with caesarean section; monitor fundal height.
• Pharmacological: gestational diabetes with glucose persistently above 5.3 mmol/L fasting or 7.8 mmol/L at 1 hour after meals despite diet: metformin 500 mg oral with meals increased to 1 g 12-hourly (maximum 2.5 g daily) or isophane insulin 0.2 units/kg subcutaneous at bedtime plus soluble insulin 4 to 6 units subcutaneous before meals; benzathine benzylpenicillin 2.4 million units IM once weekly for 3 weeks for syphilis; oxytocin 10 IU IM at birth.
• Procedures: repeat ultrasound in 2 to 4 weeks; induction at 39 weeks for idiopathic disease, 38 to 39 weeks with diabetes, with controlled amniotomy and a check for cord prolapse; caesarean section for obstetric reasons.
• Red flags: rapid increase in fundal height, breathlessness, contractions, rupture of membranes, reduced fetal movements.
• Follow-up: amniotic fluid index every 2 to 4 weeks; growth scans every 4 weeks; a nasogastric tube is passed in the newborn to exclude oesophageal atresia if there is frothing.