Fetal volume at 11-14 gestational weeks: reference ranges and association with first trimester biochemical and biophysical markers.

Aims: To establish reference ranges for fetal volume (FV) measured by three-dimensional ultrasound (3D-US) at 11-14 weeks of gestation and to examine the possible association of FV with maternal/pregnancy characteristics and biochemical parameters. Methods: Prospective observational study on 240 fetuses at 11-14 weeks. FV was measured by 3D-US using Virtual Organ Computer-Aided Analysis. Pearson correlation coefficient (cc) and regression analysis were used. Results: FV increased exponentially with crown rump length and was unrelated to maternal weight (cc=-0.137, P=0.071), age (cc=0.009, P=0.899), parity (0.76), smoking status (t-test, P=0.149) and mode of conception (t-test, P=0.8). Z-scores (z) of FV was not associated with z-mean uterine artery pulsatility index (cc=-0.026, P=0.733), log 10 multiples of the median (MoM) free beta human chorionic gonadotrophin (cc=0.002, P=0.982), delta value (d) of nuchal translucency (cc=0.072, P=0.331) and d-fetal heart rate (cc=0.009, P=0.902), z-FV was significantly positively correlated with log(10) MoM pregnancy associated plasma protein-A (PAPP-A; regression coefficient=1.420976, R-2=0.0957, P<0.0001). Conclusions: FV is strongly related to PAPP-A even after adjustment for crown rump length with a mechanism unrelated to placental perfusion. FV is independent of the vast majority of first trimester parameters; hence, it is a promising marker of early fetal growth.