Ultrasound as a primary screening tool for detecting low birthweight newborns: A meta-analysis

As low birthweight (i.e., birthweight < 2500 g) is a major determinant of neonatal mortality and morbidity, the pre-delivery detection of low birthweight is clinically advantageous. This study was performed to determine whether ultrasound is suitable for use in primary screening to detect low birthweight newborns.

The primary outcomes included sensitivity, specificity, and positive and negative likelihood ratios of ultrasound detection of low birthweight newborns. Ten databases, including PubMed, were searched. All English language studies that provided true- and false-positive and true- and false-negative results regarding the pre-delivery ultrasound detection of low birthweight newborns were eligible for inclusion in the analysis. Study quality was assessed using the Quality Assessment of Diagnostic Accuracy Studies. Bivariate diagnostic meta-analysis was performed and hierarchical summary receiver operating characteristic curves were constructed.

Studies of relatively good quality were included in the analysis to evaluate crown-rump length (n = 12); femur length (n = 5); formulas of Campbell, Hadlock, and Shepard (n = 9); and uterine artery blood flow (n = 7). All showed low sensitivity (=0.24-0.58) regardless of specificity (=0.60-0.96). The formulas of Campbell, Hadlock, and Shepard were usable for a confirmation strategy only (positive and negative likelihood ratios = 14.8 and 0.44, respectively), but crown-rump or femur length, and uterine artery blood flow were not usable for an exclusion or confirmation strategy (positive and negative likelihood ratios = 1.4-2.8 and 0.71-0.85, respectively).

Primary screening does not have to confirm low birthweight, but should almost always categorize low birthweight as a positive result and exclude normal birthweight. Therefore, ultrasound is not suitable as a primary screening tool to detect low birthweight newborns.