Placental volume at 11-13 weeks' gestation in the prediction of birth weight percentile. 
To determine the value of placental volume measured by 3D ultrasound at 11-13 weeks' gestation in combination with maternal characteristics and serum pregnancy-associated plasma protein-A (PAPP-A) in the prediction of small and large for gestational age (SGA and LGA) neonates.  Maternal serum PAPP-A and placental volume were measured at 11-13 weeks in 3,104 singleton pregnancies.  Regression analysis was used to examine the contribution of maternal characteristics, placental volume and PAPP-A in the prediction of SGA and LGA neonates.  There was a significant association between placental volume and PAPP-A (r = 0.268, p < 0.0001).  Median placental volume and PAPP-A, expressed as multiples of the median (MoM) in appropriate for gestational age (AGA) neonates, were reduced in the SGA group (placental volume 0.88 MoM, vs. 1.00 MoM in AGA, p < 0.0001; PAPP-A 0.92 MoM vs. 1.00 MoM in AGA, p = 0.019) and increased in the LGA group (placental volume 1.09 MoM vs. 1.00 MoM in AGA, p < 0.0001; PAPP-A 1.15 MoM vs. 1.00 MoM in AGA, p = 0.015).  Maternal characteristics with either placental volume or PAPP-A detected about 30% of the SGA or LGA neonates, at a false positive rate of 10%.  Measurement of placental volume and serum PAPP-A can improve the prediction of SGA or LGA neonates provided by maternal characteristics alone.