Fetal macrosomia

Last revised by Dr Henry Knipe on 12 Nov 2020

Fetal macrosomia (also sometimes termed large for gestational age) is usually defined when the estimated fetal weight (EFW) is greater than the 90th percentile. According to this definition, it affects up to 10% of all live births. Some also use an increased birth weight (i.e. >4500g) in its definition. 

Certain authors also use the 95th centile as the cut off and according to this definition, ~5% of fetuses would be affected 8.

It typically presents in the 3rd trimester. There may be some predilection for male fetuses.

Often manifests with truncal obesity and therefore the abdominal circumference (AC) will be one of the first parameters to increase. The AC is also considered one of the best parameters 8.

According to some reports, an EFW of >4000 g within a week's window from birth along with an increased amniotic fluid index (>20 cm) and relevant clinical factors are associated with fetal macrosomia at birth in ~70% of cases 3.

Early delivery or elective Cesarian section are management options. Prognosis in a majority of cases is usually good.

Most complications are related to issues with delivery and include:

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