Labour with Fetal Macrosomia

Labour with fetal macrosomia is labour in which the baby is expected to weigh more than 4000 g, or above the 95th centile for gestation. It results from maternal diabetes, obesity, excess weight gain, post term pregnancy, previous macrosomic baby and constitutional size. It matters because it raises the risk of shoulder dystocia, birth injury, prolonged labour, postpartum haemorrhage and caesarean section, and ultrasound weight estimates are wrong by up to 15 percent.

• Risk factors: diabetes (including undiagnosed gestational diabetes), body mass index above 30 kg/m2, gestation above 41 weeks, previous large baby, male fetus, age above 35 years.
• Shoulder dystocia risk rises with birth weight and is higher in diabetic women.
• Planned management starts before labour.

Fundal height is above dates and the fetus feels large, with a high or poorly fitting head. Progress in labour may be slow, and the second stage prolonged.

• Fundal height 3 cm or more above dates.
• Maternal discomfort and breathlessness.
• Differential diagnosis: wrong dates, polyhydramnios, multiple pregnancy, fibroid, constitutionally large baby, hydrops, abdominal mass.
• Complications: shoulder dystocia, brachial plexus injury, clavicle fracture, perineal tears, postpartum haemorrhage, uterine rupture, prolonged labour, caesarean section, neonatal hypoglycaemia.

The approach is to estimate fetal weight and check for diabetes before and early in labour.

• Ultrasound: estimated fetal weight, abdominal circumference above the 95th centile, liquor volume; accept an error of up to 15 percent.
• 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, if not done; capillary glucose in labour.
• Pelvic assessment and review of past birth weights and shoulder dystocia.
• Cardiotocography throughout labour.

The principle is to counsel on options, deliver in a facility with senior staff, monitor progress closely and be ready for shoulder dystocia.

• Supportive: birth in a facility able to do caesarean section; senior obstetrician and neonatal team informed; empty the bladder; maternal position changes; continuous cardiotocography; two cannulae; group and cross-match; shoulder dystocia drill reviewed.
• Pharmacological: insulin infusion 1 to 2 units per hour with hourly glucose (target 4 to 7 mmol/L) in diabetic women; oxytocin 10 IU in 1 litre Ringer's lactate (10 mU/mL) started at 12 mL per hour (2 mU/minute) and doubled every 30 minutes to a maximum of 192 mL per hour (32 mU/minute) for inadequate contractions without disproportion; cefazolin 2 g IV as a single dose before caesarean section; oxytocin 10 IU IM after birth, then 20 IU in 1 litre at 125 mL per hour for 4 hours; tranexamic acid 1 g IV over 10 minutes if bleeding exceeds 500 mL.
• Procedures: induction at 38 to 39 weeks for diabetes or a large baby, or elective caesarean section when estimated fetal weight is above 4500 g in diabetic women or above 5000 g in non diabetic women; avoid mid cavity vacuum or forceps with a large baby; shoulder dystocia manoeuvres (McRoberts position, suprapubic pressure, delivery of the posterior arm, rotational manoeuvres) if needed; episiotomy when it helps; caesarean section for arrest of dilatation or descent.
• Special groups: newborns of diabetic women 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; a woman with a previous shoulder dystocia is offered caesarean section.
• Red flags: prolonged second stage, turtle sign, abnormal fetal heart rate, bleeding above 500 mL, scar pain.
• Follow-up: newborn weight, glucose and arm movement checks; maternal perineal care; glucose test at 6 to 13 weeks postpartum for gestational diabetes; review at 6 weeks.