Épaisseur de la clarté nucale A 11–14SA : courbes et équations françaises

The introduction of the absolute risk for the detection of fetal aneuploidies in the first-trimester screening

PURPOSE

Maternal age is a crucial factor in fetal aneuploidy screening, resulting in an increased rate of false-positive cases in older women and false-negative cases in younger women. The absolute risk (AR) is the simplest way to eliminate the background maternal age risk, as it represents the amount of improvement of the combined risk from the maternal background risk. The aim of this work is to assess the performance of the AR in the combined first-trimester screening for aneuploidies.

MATERIALS AND METHODS

A retrospective validation of the AR in the combined first-trimester screening for fetal aneuploidies, in an unselected population at Altamedica Fetal-Maternal Medical Center in Rome, between March 2007 and December 2008.

RESULTS

Of 3845 women included in the study, we had a complete follow-up on 2984. We evaluated that an AR < 3 would individuate 22 of 23 cases of aneuploidy with a detection rate of 95.7% (95%CI 87.3-100), a false-positive rate of 8.7% (95%CI 7.7-9.7) and a false-negative rate of 4.3% (95%CI 0-12.7).

CONCLUSIONS

In our study, the AR ameliorates the detection rate for aneuploidy. Further research and a prospective study on a larger population would help us to improve the AR in detecting most cases of aneuploidy.

Effects of exogenous progesterone on fetal nuchal translucency: an observational prospective study

OBJECTIVE

Nuchal translucency (NT) seen ultrasonographically at 11-14 weeks' gestation is a sensitive marker for Down syndrome. Despite its important role for Down syndrome screening, its use is still considered controversial due to high false-positive rates. We speculated that progesterone could lead to abnormal blood flow patterns and, subsequently, to increased NT. Our primary endpoint was to evaluate the effects of exogenous progesterone on NT thickness compared to controls. The secondary endpoint was to evaluate these effects in a subgroup at low risk for fetal aneuploidies, identifying the strongest factors influencing NT variation. The tertiary endpoint was to evaluate, within the treatment group, if there is any difference in NT according to the type of progesterone administered, route of administration, and dose regimen.

STUDY DESIGN

All women who came to measure NT at 11-14 weeks' gestation (crown-rump length between 45-84 mm) were considered eligible. We divided patients into 2 groups: women receiving exogenous progesterone and controls. Afterwards, 3 NT scans were performed for each case, and the largest value, accurate to 2 decimal points, was recorded.

RESULTS

In all, 3716 women were enrolled and analyzed. In a crude analysis, NT (P < .05) increased in the exogenous progesterone group. The same results were obtained in the low-risk group (P < .05). The factorial analysis of variance model confirmed a correlation between altered NT and gestational age (P < .0001) and progesterone exposure (P < .05). The characteristics of treatment (route, formulation, dose) were examined separately and no statistically significant differences among the subgroups were observed.

CONCLUSION

Exogenous progesterone increases NT.

Fetal nuchal translucency thickness in different cut-off points for aneuploidy screening in the south of Vietnam

AIMS

The purpose of this study was to define the most suitable cut-off point for fetal nuchal translucency thickness in a screening program for aneuploidy and trisomy 21 in the south of Vietnam.

MATERIAL & METHODS

Two thousand and five hundred cases of singleton pregnancies were followed prospectively from the first trimester to the delivery. The rate of aneuploidy was calculated by seeking a relationship to increased fetal nuchal translucency thickness then calculating the sensitivity and specificity of different cut-off points in thickness measurement to find the most suitable point for screening.

RESULTS

The prevalence of fetal abnormality was 1.5% (95% CI 1.1-2.1), and 1.2% (95% CI 0.8-1.7) of aneuploidy cases found and the commonest was trisomy 21. A cut-off point at 2.4 mm showed the highest level of sensitivity and specificity for the detection of aneuploidy (65.5 and 95.7%) and trisomy 21 (75.0 and 95.1%), with a false-positive rate of 4.3 and 4.9%, respectively.

CONCLUSION

Using a cut-off point of nuchal translucency at 2.4 mm has potential for aneuploidy and trisomy 21 screening in the south of Vietnam.

Likelihood ratio-based quality control for nuchal translucency measurements at 11-14 weeks of gestation

OBJECTIVE

To develop a quantitative quality control process of nuchal translucency (NT) measurement at 11-14 weeks of gestation based on the mixture model, characterized by analysis of the corresponding distribution of the likelihood ratio (LR).

METHODS

Based on the published mixture model for NT measurement in the first trimester, we simulated the expected distribution of NT and the corresponding LR. This approach was then tested for the quality control of 15 048 NT measurements performed by four operators trained and certified by The Fetal Medicine Foundation. The new quality control approach based on LR was compared with existing processes based on NT plots, multiples of the median (MoMs) and analysis of the 95(th) centile.

RESULTS

Each operator contributed 2176-4730 examinations. Median, 5(th) and 95(th) centile of NT values ranged from 1.4 to 1.6, 1.0 to 1.0 and 2.2 to 2.6 mm, respectively. Median of NT-MoM values ranged from 0.83 to 0.95. Analysis of the distribution of NT measurements confirmed departure from the assumptions of the delta-NT and NT-MoM models. Analysis of LR distributions demonstrated a significant difference between observed and expected distributions for all operators (P < 10(-4) ).

CONCLUSION

An LR-based quality control process is feasible at 11-14 weeks of gestation. Because it is more sensitive to measurement bias around the critical area of the 95(th) centile, its use should be encouraged.