Gestational sac volume measured by three‐dimensional ultrasound at 11 to 13 + 6 weeks of gestation: relation to chromosomal defects

Abstract

To determine the potential value of measuring the gestational sac volume (GSV) at 11 to 13 + 6 weeks of gestation in screening for chromosomal defects. The GSV was measured using three-dimensional (3D) ultrasound in 500 consecutive singleton pregnancies immediately before chorionic villus sampling (CVS) for fetal karyotyping at 11 to 13 + 6 (median 12) weeks of gestation. The fetal karyotype was normal in 417 pregnancies and abnormal in 83. In the chromosomally normal group, the mean GSV increased significantly with gestational age from a mean of 69 mL at 11 weeks to 144 mL at 13 + 6 weeks (the standard deviation was 27 mL). In the chromosomally abnormal group, the mean GSV for gestational age was not significantly different from normal in fetuses with trisomy 21, trisomy 18 and Turner syndrome, but it was smaller in those with triploidy and trisomy 13. However, the mean GSV for crown-rump length (CRL) was significantly larger in trisomy 18, smaller in triploidy and trisomy 13, and not different from normal in trisomy 21 and Turner syndrome. The mean CRL for gestational age was significantly smaller than normal in trisomy 18, triploidy and trisomy 13. The measurement of the GSV at 11 to 13 + 6 weeks of gestation is unlikely to provide useful prediction of the major chromosomal defects. In trisomy 13 and triploidy, the small GSV may be due to early onset fetal growth restriction and reduced amniotic fluid volume. In trisomy 18, the increase in GSV is probably due to the presence of associated fetal abnormalities that interfere with fetal swallowing.