Embryonic reference values for nuchal translucency thickness and ductus venosus blood flow at 8-10 + 6 gestational weeks.

PURPOSE: To measure embryonic nuchal translucency (NT) thickness and ductus venosus (DV) blood flow indices using transvaginal two-dimensional sonography and Doppler ultrasound at 8-10 + 6 weeks.

METHODS

Transvaginal scans were performed for 149 normal and three abnormal embryos (trisomy 18 with ventricular septal defect (VSD), tricuspid insufficiency (TR), and intrauterine fetal death with trisomy 21) at 8-10 + 6 weeks. NT thickness, S wave (cm/s), D wave (cm/s), "a" wave (cm/s), S/a, pulsatility index (PI), and resistance index (RI) of DV were measured, and reference values for each parameter were determined.

RESULTS

NT, S, D, S/a, PI, and RI increased linearly with advancing gestation (p < 0.01). The 'a' (mean, 5.55 cm/s; SD, 1.8 cm/s) value was constant at 8-10 + 6 weeks of gestation. There were significant linear correlations between NT, S, D, S/a, PI, and RI, and crown-rump length (CRL) (p < 0.01). The "a" value remained unchanged with increasing CRL during this period. NT thickness (2.8 mm) in the trisomy 18 patient with VSD was high at 10 + 6 weeks, and reversed "a" wave was evident in the patient with TR at 10 + 1 weeks. In a fetus with intrauterine fetal death with trisomy 21 at 11 weeks and 6 days, NT thickness was 2.1 mm, and reversed DV flow was noted at 9 weeks and 6 days.

CONCLUSION

Our results provide reference values for NT thickness and DV flow parameters, which may advance our understanding of embryonic growth and promote earlier prenatal diagnosis of chromosome abnormalities and/or cardiac anomalies before 11 weeks.