Diabetes with Fetal Macrosomia

Diabetes with fetal macrosomia is diabetes of any type in pregnancy with an estimated fetal weight above the 90th centile, abdominal circumference above the 95th centile or birth weight above 4000 g. Maternal hyperglycaemia drives fetal hyperinsulinism and fat deposition. It matters because it raises the risk of shoulder dystocia, birth injury, caesarean section, postpartum haemorrhage and neonatal hypoglycaemia.

• Abdominal circumference growth above the 75th centile at 28 to 32 weeks signals poor control.
• Shoulder dystocia risk rises steeply at birth weight above 4500 g in diabetes.
• Tight glucose control reduces the risk.

Fundal height is larger than gestation, and women report heavy fetal movements, breathlessness and discomfort. Examination may show polyhydramnios and a large head and body.

• Fundal height more than 3 cm above dates.
• Glucose readings often above target.
• Differential diagnosis: polyhydramnios, wrong dates, multiple pregnancy, uterine fibroid, constitutional large baby.
• Complications: shoulder dystocia, brachial plexus injury, clavicle fracture, perineal tears, postpartum haemorrhage, caesarean section, neonatal hypoglycaemia and respiratory distress.

The approach is serial ultrasound with glucose review.

• Ultrasound at 28, 32 and 36 weeks: abdominal circumference and estimated fetal weight, liquor volume.
• Estimated fetal weight above 4000 g or abdominal circumference above the 95th centile confirms macrosomia; ultrasound error is up to 15 percent.
• Capillary glucose profile; targets fasting 3.5 to 5.3, 1 hour below 7.8, 2 hours below 6.4 mmol/L; HbA1c.
• Pelvic assessment and previous delivery history.

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

• Supportive: dietitian review; walking 30 minutes after meals; counselling on delivery choices; delivery in a facility with surgical and neonatal care.
• Pharmacological: intensify insulin by 2 units or 10 percent every 2 to 3 days (isophane insulin 0.2 units/kg at bedtime plus soluble insulin 0.1 units/kg before each meal as the starting plan); add metformin 500 mg oral with meals to 1 g 12-hourly (maximum 2.5 g daily); for induction use misoprostol 25 micrograms vaginal 6-hourly (maximum 4 doses) if there is no uterine scar, or a Foley catheter with 30 mL balloon if there is a scar; oxytocin infusion starting at 2 mU/minute, doubling every 30 minutes to a maximum of 32 mU/minute; oxytocin 10 IU IM after delivery of the baby; tranexamic acid 1 g IV over 10 minutes if bleeding exceeds 500 mL.
• 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: call for help, McRoberts position, suprapubic pressure, rotational manoeuvres, 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, turtle sign at delivery, prolonged second stage, glucose below 3.5 mmol/L.
• Follow-up: growth scans every 2 to 4 weeks from 28 weeks; glucose review weekly; postnatal glucose test or HbA1c at 6 to 13 weeks for gestational diabetes.