Sonographic birth-weight prediction in obese patients using the gestation-adjusted prediction method

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Medical Imaging

Background:

• Ultrasound is a key tool for predicting fetal birth weight.
• Accuracy of ultrasound birth weight prediction can be reduced in women with elevated body mass index (BMI).
• The gestation-adjusted projection (GAP) method offers a way to improve ultrasound-based birth weight prediction.

Purpose of the Study:

• To assess the accuracy of the GAP method for predicting birth weight in obese versus non-obese pregnant women.
• To determine if maternal BMI affects the reliability of the GAP method for birth weight prediction.
• To evaluate the GAP method's effectiveness in excluding fetal macrosomia across different BMI categories.

Main Methods:

• Retrospective review of 1382 singleton pregnancies with fetal ultrasound at 34 to 36+6 weeks gestation.
• Participants were subclassified based on pre-pregnancy BMI into control and obese groups (Class I, II, III).
• Analysis of variance was used to compare predicted and actual birth weights, assessing prediction error and accuracy in identifying macrosomia.

Main Results:

• Mean birth weight prediction error for the GAP method was within 4% across all BMI groups, with a 95% error range of -5% to +5%.
• The GAP method predicted actual birth weight within 20% error in over 90% of cases for all groups.
• The method demonstrated over 90% specificity in excluding macrosomia, with negative likelihood ratios between 0.4 and 0.6, irrespective of maternal obesity.

Conclusions:

• The GAP method, utilizing ultrasound measurements between 34 and 36+6 weeks gestation, provides accurate birth weight predictions.
• This prediction method is effective within a 20% error margin in over 90% of cases, regardless of maternal BMI.
• The GAP method reliably excludes fetal macrosomia with over 90% accuracy, making it a valuable tool for all pregnant women.