Significance of Biparietal Diameter Differences between Twins

Abstract

Ultrasound scanning provides a safe and accurate diagnostic technique for identifying twin pregnancies as well as measuring the biparietal diameters (BPD) of individual twin fetuses. The ability to evaluate each twin separately is of paramount importance, as twins of dissimilar size have both increased risks at delivery and in the neonatal period. Dissimilar twin growth, when severe, should be reflected in differences in birth weight and diameter. A 25% difference in fetal weight has been found to significantly alter height, weight, head circumference, and IQ score in grade school when compared to the larger twin. Paradoxically, the small-for-dates infant gains weight faster, has fewer respiratory problems, and is discharged sooner than prematures of similar weight. This study was undertaken to determine if the difference in BPD could be useful as an estimate of relative fetal growth between individual fetuses.