By Martha Kerr
The method and its rate of accuracy are described in the journal Ultrasound in Obstetrics and Gynaecology.
Principal researcher Dr. Loralei L. Thornburg and colleagues at the University of Rochester, New York, reviewed the records of 1 382 pregnant women who underwent foetal ultrasound examinations when they were 34 to 36 weeks pregnant.
The group consisted of 357 obese women and 1 025 non-obese women. The obese women were further divided into three groups based on the severity of their obesity.
The ultrasound-based calculation "was able to predict actual birth weight within 20 percent for all groups in over 90 percent of cases," the research team reports. The test was also very good in determining whether the baby would be abnormally large.
"In general, ultrasound in pregnancy is one of the greatest tools available to the obstetrician, allowing us to objectively measure and evaluate the foetus," Thornburg commented during an interview with Reuters Health.
"Obesity, especially morbid obesity, significantly limits the visualisation and evaluation of the foetus by ultrasound... The greatest value of the (new calculation) method in obesity is the ability to exclude (abnormally large babies) in all groups of obese patients, and improve our ability to counsel patients regarding risks and delivery options," she said.
"Obese patients often require more ultrasounds during pregnancy than their non-obese counterparts, since monitoring and evaluation of foetal growth by physical examination in the obese patient is more difficult," Thornburg pointed out.