Sonographic birth-weight prediction in obese patients using the gestation-adjusted prediction method.
OBJECTIVE
Ultrasound birth-weight prediction may be more accurate if assessed at 34 to 36 + 6 weeks' gestation and extrapolated using the gestation-adjusted projection (GAP) method than if done at term. Because ultrasound is less accurate in women with elevated body mass index (BMI), we assessed the accuracy of GAP birth-weight prediction in obese as compared to non-obese women.


METHODS
We performed a retrospective review of 1382 women with singleton pregnancies who had undergone fetal ultrasound examination at between 34 + 0 and 36 + 6 weeks, subclassified by pre-pregnancy BMI. Analysis of variance was used to compare predicted and actual birth weight.


RESULTS
1025 controls and 357 obese women were included. The obese women were divided by BMI: 159 in Class I (BMI, 30-34.9 kg/m(2)); 105 in Class II (BMI, 35-40 kg/m(2)) and 93 in Class III (BMI > 40 kg/m(2)). Mean systematic (percent) birth-weight prediction error was within 4% for all groups, with a 95% error range between - 5% and + 5%. The GAP method was able to predict actual birth weight within 20% for all groups in over 90% of cases. For all groups, the GAP method correctly excluded the presence of macrosomia with >or= 90% specificity. Negative likelihood ratios for the prediction of macrosomia were between 0.4 and 0.6 for all groups, regardless of obesity.


CONCLUSIONS
The GAP method of birth-weight prediction using ultrasound measurement at 34 to 36 + 6 weeks predicts birth weight within 20% error in over 90% of cases, and is able to exclude macrosomia with over 90% accuracy regardless of maternal BMI.
Department of Obstetrics and Gynecology, Division of Maternal Fetal Medicine, University of Rochester Strong Memorial Hospital, Rochester, NY, USA. loralei_thornburg@urmc.rochester.edu
L L
LL
Thornburg
C
C
Barnes
J C
JC
Glantz
E K
EK
Pressman
D000328:Adult; D000886:Anthropometry / Q000379:methods*; D001724:Birth Weight; D015992:Body Mass Index; D016022:Case-Control Studies; D005260:Female; D005320:Fetal Macrosomia / Q000000981:diagnostic imaging; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D009518:New York; D009765:Obesity / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000000981:diagnostic imaging*; D011263:Pregnancy Trimester, Third; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal