Gestational Diabetes with Macrosomia

Gestational diabetes with macrosomia is glucose intolerance first found in pregnancy with a fetus above the 90th centile or an abdominal circumference above the 95th centile.

Fetal hyperinsulinism from maternal hyperglycaemia causes excess growth. It matters because it raises the risk of shoulder dystocia, birth trauma, caesarean section, postpartum haemorrhage and neonatal hypoglycaemia.

Risk factors: maternal obesity, excessive weight gain, previous macrosomia, post term pregnancy.

Good glucose control reduces the risk.

Ultrasound weight estimates are accurate to about 15 percent.

Fundal height is more than 3 cm above dates, with large fetal parts and sometimes polyhydramnios. Women may report breathlessness and discomfort.

Glucose often above target.

Excess weight gain.

Differential diagnosis: wrong dates, polyhydramnios, multiple pregnancy, uterine fibroid, constitutional large baby, preexisting diabetes.

Complications: shoulder dystocia, brachial plexus injury, perineal tear, postpartum haemorrhage, caesarean section, neonatal hypoglycaemia, later obesity and diabetes in the child.

The approach is ultrasound with glucose review.

• 75 g oral glucose tolerance test: fasting 5.1 mmol/L or above, 1 hour 10.0 mmol/L or above, 2 hours 8.5 mmol/L or above.
• Ultrasound at 28, 32 and 36 weeks: abdominal circumference, estimated fetal weight, liquor volume.
• Capillary glucose profile with targets fasting below 5.3, 1 hour below 7.8, 2 hours below 6.4 mmol/L; HbA1c.
• Pelvic assessment and past delivery history.

The principle is tight glucose control and a planned delivery with shoulder dystocia preparation.

• Supportive: dietitian review; walking 30 minutes after meals; limit weight gain; counselling on mode of delivery.
• Pharmacological: start 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 as soon as targets are missed or abdominal circumference is above the 90th centile; adjust by 2 units every 3 days; induction with misoprostol 25 micrograms vaginal 6-hourly (maximum 4 doses) or Foley catheter 30 mL balloon if scarred uterus; oxytocin infusion starting at 2 mU/minute and doubling every 30 minutes to a maximum of 32 mU/minute; oxytocin 10 IU IM after delivery of the baby.
• Procedures: induction of labour at 38 weeks to 38 weeks and 6 days; elective caesarean section if estimated fetal weight is above 4500 g; shoulder dystocia drill with McRoberts position, suprapubic pressure, rotational manoeuvres and delivery of the posterior arm.
• Special groups: neonates feed within 30 minutes, check glucose at 2 to 4 hours, treat glucose below 2.6 mmol/L with dextrose 10 percent 2 mL/kg IV over 10 minutes; women with previous shoulder dystocia are offered caesarean section.
• Red flags: reduced fetal movements, prolonged second stage, turtle sign at delivery, bleeding above 500 mL.
• Follow-up: growth scans every 2 to 4 weeks; 75 g oral glucose tolerance test at 6 to 13 weeks postpartum; yearly HbA1c.