Placental volume measured by three-dimensional ultrasound at 11 to 13 + 6 weeks of gestation: relation to chromosomal defects.

OBJECTIVE To determine the potential value of measuring the placental volume at 11 to 13 + 6 weeks of gestation in screening for chromosomal defects. METHODS The placental volume was measured using three-dimensional ultrasound in 500 consecutive singleton pregnancies immediately before chorionic villus sampling for fetal karyotyping at 11 to 13 + 6 (median, 12) weeks of gestation. RESULTS The fetal karyotype was normal in 417 pregnancies and abnormal in 83. In the chromosomally normal group the mean placental volume increased significantly with gestation from a mean of 51 mL (5th and 95th centiles: 31.2 and 82.4 mL) at 11 weeks to 91 mL (5th and 95th centiles: 55.7 and 147.2 mL) at 13 + 6 weeks. In the chromosomally abnormal group the mean placental volume for gestational age was not significantly different from normal in trisomy 21 and Turner syndrome, but it was smaller in trisomies 13 and 18. CONCLUSIONS The measurement of the placental volume at 11 to 13 + 6 weeks of gestation is unlikely to be a useful predictor of the major chromosomal defects. In trisomies 13 and 18 the small placental volume may be due to early-onset fetal growth restriction, which could be the consequence of impaired placental function.