A comparison of symphysis-fundal height and ultrasound as screening tests for light-for-gestational age infants.

The clinical efficiency of serial measurement of symphysis-fundal height (SFH) for the prediction of light-for-gestational age (LGA) infants was compared with that of a single measurement of fetal abdominal circumference (AC) by ultrasound in the third trimester. To make the tests comparable the lower cut-off point of AC was altered until the specificity matched that of SFH. The sensitivity of the AC measurement (83%) was slightly better than that of the SFH measurement (76%) but this difference was not statistically significant. Each test had a false positive rate of about 60% which is comparable with clinical assessment. Screening with both tests and predicting LGA with abnormal results from either test improved the sensitivity to 93% but, as expected, decreased the specificity to 67% and the positive predictive value to 32%. If ultrasound facilities permit both tests should be used otherwise SFH measurements only could screen for LGA with ultrasound back-up for those with low SFH results.