Umbilical cord diameter at 11-14 weeks of gestation: relation to chromosomal defects.

OBJECTIVE To determine the potential value of measuring umbilical cord diameter (UCD) at 11-14 weeks of gestation in screening for chromosomal defects. METHODS The UCD was measured in 1323 fetuses immediately before chorionic villus sampling for karyotyping at 11-14 weeks of gestation. In the group of chromosomally normal fetuses, regression analysis was used to determine the association between UCD and crown-rump length (CRL). UCD was compared in normal fetuses and those with chromosomal abnormalities. RESULTS The median gestation was 12 (range, 11-14) weeks. The UCD was successfully measured in all cases. The fetal karyotype was normal in 1150 pregnancies and abnormal in 173, including 97 cases of trisomy 21. In the chromosomally normal group the UCD increased significantly with CRL from a mean of 2.9 mm at a CRL of 45 mm to 4.4 mm at a CRL of 84 mm. The UCD in the group of fetuses with trisomy 21 was significantly smaller than normal. Conversely, there were no significant differences from normal in the UCD of fetuses with other chromosomal abnormalities. CONCLUSION At 11-14 weeks of gestation the UCD of fetuses with trisomy 21 is significantly smaller than normal but the magnitude of the difference is too small for useful inclusion of this measurement in screening.