Ultrasound Diagnosis of Fetal Macrosomia Found Inaccurate

By: SUSAN LONDON, Family Practice News Digital Network

VANCOUVER, B.C. – An ultrasound diagnosis of fetal macrosomia at term is inaccurate in the majority of cases, and this inaccuracy may be contributing to unnecessary cesarean deliveries, new data suggest.

In an observational cohort study of 235 pregnancies at term in which ultrasound measurements led to a diagnosis of fetal macrosomia, only about a third of the infants were actually macrosomic at birth. Additionally, these pregnancies with ultrasound-diagnosed fetal macrosomia were more than twice as likely as all pregnancies in the population to end in cesarean delivery, according to results reported at the annual meeting of the Society of Obstetricians and Gynaecologists of Canada.

Ultrasound-estimated fetal weight "is not very accurate, and we have to counsel patients on that, when they come to ultrasounds and they are worried that they are going to have this [enormous] monstrosity of a baby," lead investigator Dr. Alese Wagner said in an interview. "You can tell them [that] most of the time, we are off."

She further recommended that physicians keep this new information in mind when it comes to recommending delivery interventions for a pregnancy in which the ultrasound suggests macrosomia.

Surprisingly, the accuracy of ultrasound in assessing fetal weight is similar to that found with simple clinical palpation, according to Dr. Wagner, a third-year resident in the department of obstetrics and gynecology at the University of Calgary in Alberta.

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