Evaluation of fetal femur length to detect Down syndrome in a Thai population

Evaluation of the usefulness of the fetal femur length with respect to gestational age to detect Down syndrome in Korean subjects

OBJECTIVE

We investigated the usefulness of shortening of the fetal femur length (FL) to predict Down syndrome at different gestational ages in Korean subjects.

METHODS

This study involved 110 Korean Down syndrome fetuses and 602 randomly selected euploid controls. The expected FL for any biparietal diameter (BPD) was calculated based on the control group data. Subjects were divided into four groups according to gestational age periods: 14-18 weeks; 19-23 weeks; 24-28 weeks and 29-36 weeks. The value of measured/expected FL ratio to predict Down syndrome was analyzed for each group.

RESULTS

The values of FL for any BPD in Down syndrome patients were significantly different from those in the control group (p < 0.001). A low ratio of measured/expected FL increased the risk of fetal Down syndrome (p < 0.001) with a mean measured/expected FL in Down syndrome of 0.907 (SD 0.075). At a fixed false positive rate of 5%, the sensitivities of FL were lower than 32.8% (95% CI 0.705-0.915) in three second trimester groups, and 71.1% (95% CI 0.924-0.997) in the third trimester group.

CONCLUSION

Short FL is a poor marker of Down syndrome in the second trimester in Korean subject. It may be used as a screening marker only in the third trimester.

[Role of "subtle" ultrasonographic signs during antenatal screening for trisomy 21 during the second trimester of pregnancy: meta-analysis and CPDPN protocol of the Grenoble University Hospital]

OBJECTIVE

A meta-analysis about subtle ultrasonographic signs in second trimester of pregnancy.

MATERIALS AND METHODS

196 articles dealing with the subject--from 1985 to July 2002--were studied. Data on the 11 reported signs were collected from 92 theoretically and/or statistically valid studies. Then, the studies were selected according to several criteria: isolated characteristic, defined thresholds, calculable sensitivity and specificity. After checking for homogeneity, a likelihood ratio was calculated for some of the signs.

RESULTS

This meta-analysis of the second trimester ultrasonographic signs of Down's syndrome enabled us to estimate the likelihood ratio (LHR) of six signs. At 22 weeks'gestation (WG) these signs are: pyelectasis equal to or greater than 5 mm; nuchal fold thickness equal to or greater than 6 mm; persistence of choroid plexus cysts; shortness of the femur and humerus below the tenth percentile; hyperechogenic bowe; and nasal bone length less than 2.5 mm.

CONCLUSION

These validated ultrasonographic signs are independent of nuchal translucency thickness at 12 WG and of maternal serum biochemistry. This allows to calculate a combinate risk for nuchal translucency, maternal serum biochemistry and second trimester ultrasonographic signs when they are validated.