Total intra-uterine volume and symphysis fundus height. Is there a relation?

The concordance between measurements of total intra-uterine volume (parallel planimetric area method) and symphysis fundus height and the efficacy of these measurements in predicting birthweight by centile range was prospectively investigated in a blind study of 81 measurement sets in 74 women in the third trimester of pregnancy. Gestational length was determined by early ultrasound scans in all cases. Reference curves were from separate populations. Correlation between the measurements was significant, both at 32 weeks (p = 0.015) and 36 weeks (p less than 0.001), but only 21% of the variation in intra-uterine volume at 32 weeks and 63% at 36 weeks' gestation was attributable to changes in fundal height. Intra-uterine volume was therefore not accurately reflected by fundal height. Fundal height and intra-uterine volume were in the same centile range in 34% of cases. Maternal height and weight did not correlate with intrauterine volume, but there were significant relations with fundal height, particularly at 36 weeks. Birthweight correlated better with volume (r = 0.665) than with fundal height (r = 0.461) at 32 weeks, while at 36 weeks there was little difference (r = 0.691 and 0.794). In 54% of volume and 47% of symphysis fundus measurements there was agreement with the same centile range of birthweight. Predictive capacity of volume measurements appeared better for the lower birthweight ranges.