Intrapartum Ultrasonography for Detecting Fetal Macrosomia

Objective: To compare the accuracy of three ultrasound methods to estimate fetal weight within 48 hours before delivery, in order to recognize macrosomia, defined as birth weight greater than 4000 g. Methods: A prospective and ultrasonic study was performed on a sample of singleton pregnancies between 37 weeks and 41 weeks plus 6 days of gestation. Fetal weight was evaluated with Estimated Fetal Weight (EFW) formula, with the measurement of the Abdominal Circumference (AC) and with the assessment of the Abdominal Circumference corrected with the constant “c” (ACc). Results: 1030 patients with single pregnancy were included, 67.28% of them were primiparous, average Body Mass Index (BMI) at birth was 27.37 and macrosomia was found in 77 (8,08%) fetuses. EFW showed a sensitivity of 61.53%, a specificity of 90.72%, a positive predictive value (PPV) of 27.58% and negative predictive value (NPV) of 97.46%, to recognize birth weight of more than 4000 g. AC greater than 375 mm presented a sensitivity of 53.24%, a specificity of 93.21%, a PPV of 41.41% and a NPV of 95.67%, to detect macrosomic fetuses. ACc greater than 375 mm showed a sensitivity of 66.23%, a specificity of 88.65%, a PPV of 34.35% and a NPV of 96.68%, to predict macrosomia. The mean absolute error when the neonatal weight was greater than 4000 g, with EFW was 9,23%, with AC were 11,02% and with ACc was 9,32%. Conclusions: In this study was shown that either EFW, or AC-only, or ACc are useful tools to detect fetal macrosomia. The measurement of AC and Acc seem to be the easiest methods to learn and to be used every time. During the first stage of labor, ultrasound scan associated to clinic evaluation, provides further elements to physician, to allow a better management of delivery. The finding of a NPV greater than 95% with the three methods, leads to exclude macrosomia with a good approximation, even in case of clinic hypothesis