What is Large for Gestational Age (macrosomia)?

Large for gestational age, or macrosomia (LGA) is defined in the UK (see NICE guideline NG207) as an estimated fetal weight (EFW) above the 95th centile at or after 36 weeks.

There are many causes for LGA. The commonest cause is constitutional – which means healthy and large – often there is strong family history of bigger babies being born in the parents’ families with no ill effects. Other causes include diabetes, and very rare cases, there may be an underlying genetic syndrome of overgrowth.

You obstetrician will talk you through your birth options if you are carrying a large baby. You have 3 options: conservative management (waiting for labour to start naturally), induction of labour, and rarely if the baby is thought to be very large, elective caesarean birth.

There is uncertainty about the benefits and risks of induction of labour compared to expectant management, but:
－ with induction of labour the risk of shoulder dystocia is reduced compared with expectant management
－ with induction of labour the risk of third- or fourth-degree perineal tears is increased compared with expectant management
－ there is evidence that the risk of perinatal death, brachial plexus injuries in the baby, or the need for emergency caesarean birth is the same between the 2 options.

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