Optimising the timing for nuchal translucency measurement

Abstract

It appears from current evidence that the most effective screening strategy for Down syndrome will involve a combination of first trimester nuchal translucency and serum biochemistry, whether performed in the first or second trimester. The aim of this study was to determine the optimum gestation based upon menstrual dates at which to schedule nuchal translucency (NT) measurement for the evaluation of fetal Down syndrome risk. Five thousand eight hundred and thirty-five pregnancies had an ultrasound scan scheduled between 11 and 14 completed weeks of gestation based upon either the last menstrual period (n = 3199) or a prior ultrasound scan (n = 2636). For last menstrual period-based ultrasound scans, with advancing gestation the frequency of missed miscarriage significantly decreased (p = 0.009, chi squared test), as did the need to reschedule a further scan because the gestation of the scheduled scan was too early to measure NT (p < 0.0001, Chi-squared test). In contrast, with advancing gestation the rate of unsuccessful NT measurement because the crown-rump length (CRL) was greater than 84 mm significantly increased (p < 0.0001, Chi-squared test). Of the women who had had an earlier ultrasound, 42 (1.6%) had a missed miscarriage and 9 (0.3%) were over gestation at the time of the NT scan. These data suggest that when only the last menstrual period is known the optimum time to schedule a nuchal translucency measurement is at 12 to 13 weeks' gestation.

The Value of Repeated Evaluation After Initial Failed Nuchal Translucency Measurement

“…Similarly, physicians referring patients for NT screening can improve resource utilization by ensuring that women are scheduled at 12 to 13 weeks by menstrual dates, thereby decreasing the frequency of failed measurements for a CRL of less than 45 mm. 10 Finally, NT programs will require such data to optimally manage patient bookings, including scanning time, increased TVUS use, and followup visits as indicated.…”

Optimal crown–rump length for measuring the nuchal translucency

“…Not surprisingly, 8-12% of women referred for NT screening on the basis of menstrual dating are too early based on CRL or have an undiagnosed miscarriage. 3,4 Therefore, scheduling the NT evaluation at 12-13 weeks by menstrual dating improves the NT success rate. 3 However, this approach may not be valid in pregnancies with sonographically determined dating.…”

“…3,4 Therefore, scheduling the NT evaluation at 12-13 weeks by menstrual dating improves the NT success rate. 3 However, this approach may not be valid in pregnancies with sonographically determined dating. Therefore, we performed a retrospective cohort study to determine the optimal CRL for obtaining NT measurements and the reasons for failed attempts.…”

Promises and pitfalls of first trimester sonographic markers in the detection of fetal aneuploidy

“…However, screening for trisomy 21 is not the only goal of first trimester ultrasound, because detection of an increasing number of structural anomalies is feasible from 12 weeks onwards. When the effect of unsuccessful scans, secondary to issues as a nonviable pregnancy or the pregnancy being outwit the required gestation is taken into account, the optimal time again appear to be 12-13 weeks (Mulvey et al, 2002).…”