Polyhydramnios Secondary to Diabetes

Polyhydramnios secondary to diabetes is excess amniotic fluid in a woman with preexisting or gestational diabetes, caused by fetal hyperglycaemia leading to fetal polyuria and increased fluid production. It matters because it is a marker of poor glucose control and macrosomia and carries risks of preterm labour, cord prolapse and postpartum haemorrhage.

• Risk factors: HbA1c above 7 percent, obesity, macrosomia, late diagnosis of diabetes.
• Appears after 28 weeks.
• Improves with tight glucose control.

Women have a large uterus for dates, breathlessness, discomfort and oedema, and glucose readings are often above target. Fetal parts are difficult to feel.

• Fundal height 3 cm or more above dates.
• Thirst, polyuria and recurrent candidiasis.
• Differential diagnosis: idiopathic polyhydramnios, fetal swallowing disorder, fetal anomaly, fetal anaemia, multiple pregnancy, macrosomia, infection.
• Complications: macrosomia, shoulder dystocia, preterm labour, cord prolapse, abruption, postpartum haemorrhage, neonatal hypoglycaemia, stillbirth.

The approach is ultrasound with glucose profile and exclusion of other causes.

• Ultrasound: amniotic fluid index above 24 cm or deepest vertical pocket above 8 cm; abdominal circumference, estimated fetal weight, anomaly scan, fetal heart scan.
• Capillary glucose profile: fasting, 1 hour after each meal and at bedtime (targets fasting 3.5 to 5.3, 1 hour below 7.8 and 2 hours below 6.4 mmol/L); HbA1c; urine ketones.
• Maternal blood group and antibody screen, syphilis, TORCH serology, parvovirus B19.
• Amniocentesis for karyotype when anomalies are found.

The principle is tight glucose control, relief of symptoms and planned delivery at 38 to 39 weeks.

• Supportive: dietitian review with 40 to 45 percent carbohydrate; walking 30 minutes after meals; rest; counselling about preterm labour and cord prolapse; deliver in a facility with caesarean section and neonatal care.
• Pharmacological: isophane insulin 0.2 units/kg subcutaneous at bedtime plus soluble insulin 4 to 6 units subcutaneous 30 minutes before meals, adjusted by 2 units every 3 days; metformin 500 mg oral with meals increased to 1 g 12-hourly (maximum 2.5 g daily); indomethacin 25 mg oral 6-hourly for no more than 48 hours before 32 weeks for symptomatic severe disease, with repeat scan of the ductus arteriosus; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if delivery is likely, with insulin increased by 25 to 40 percent for 72 hours; 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 litres, no faster than 1 litre per 20 minutes, for tense symptomatic disease; induction at 38 to 39 weeks with controlled amniotomy; elective caesarean section if estimated fetal weight is above 4500 g; in labour hourly glucose (target 4 to 7 mmol/L) with soluble insulin infusion 1 to 2 units per hour for glucose above 7 mmol/L.
• Special groups: newborns feed within 30 minutes and 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; after delivery insulin is stopped in gestational diabetes and reduced to the pre-pregnancy dose in type 1 or type 2 diabetes.
• Red flags: glucose above 15 mmol/L, ketones, contractions, rupture of membranes, breathlessness, reduced fetal movements.
• Follow-up: amniotic fluid index every 2 weeks; growth scans every 2 to 4 weeks; 75 g oral glucose tolerance test at 6 to 13 weeks postpartum for gestational diabetes; yearly HbA1c.