Are there specific factors associated with prenatally undiagnosed foetal macrosomia?

Objective: Fetal macrosomia is known to increase maternal and neonatal complications, but 20%-50% of the macrosomic fetuses are prenatally undiagnosed. Our objective was to identify specific factors associated with undiagnosed fetal macrosomia in women without diabetes.

Methods: Retrospective case-control study in a tertiary maternity unit between January 1st and December 31st, 2016. Inclusion of all women delivering after 37 weeks of a single live-born macrosomic infant, i.e., with a birth weight ≥ 90th percentile for gestational age (GA). Women with pre-existing or gestational diabetes were excluded. To identify specific factors associated with undiagnosed foetal macrosomia, we compared risk factors for macrosomia, maternal characteristics, father's body mass index (BMI) and prenatal follow up between two groups depending on whether macrosomia was prenatally diagnosed or not.

Results: Among 428 macrosomic newborns, 224 (52.3 %) were prenatally undiagnosed. Known risk factors for macrosomia, maternal characteristics (such as low socio-economic level, low education level) and father's BMI were similar between the two groups. The prenatal follow up was comparable between the two groups. Ultrasound estimated foetal weight during the 3rd trimester was lower in the undiagnosed macrosomic foetuses compared to diagnosed macrosomic foetuses (2130±279 vs 2445±333, p<0.001).

Conclusions: No specific factor of undiagnosed macrosomia was identified, and women with prenatally undiagnosed fetal macrosomia had the same risk factors than women with diagnosed macrosomia. Our study suggests that our groups have different growth curves. This hypothesis has yet to be studied.