Duke University Medical Center
say ultrasounds are valuable tools during pregnancy, but may not be the best way to calculate birth weight.
Miscalculations in birth weight cannot always detect macrosomia, a condition when a baby weighs more than 8 pounds, 13 ounces or more at birth.
"Eighty percent of babies that have this condition can't be identified properly through ultrasound," said obstetrician Dr. Gerard Nahum.
Nahum said a new formula is making better birth weight predictions.
"We can predict at 37 weeks how big the baby is, and then at 38, 39, and all the way up to 42 weeks," he said.
Six factors are considered in the equation: The mother's height, weight before pregnancy, her third trimester weight gain, the mother's gestational age at delivery, number of previous pregnancies and the baby's sex.
Nahum then inserts the information into an equation and calculates birth weight.
"We can pick up more than 50 percent of babies who have this condition of being too large," Nahum said.
According to a new study, the formula is accurate within a pound and is expected to decrease risk for the mother in the delivery room.