Second-Trimester Screening for Trisomy-21 Using Prefrontal Space Ratio

Abstract

Objective: To investigate the potential value of prefrontal space ratio (PFSR) in second-trimester screening for trisomy-21. Methods: A retrospective study utilizing stored midsagittal two-dimensional images of fetal profiles in 240 euploid and 45 trisomy-21 pregnancies at 16⁺⁰-23⁺⁶ weeks' gestation. The vertical distance between the leading edge of the skull and that of the skin (D1) and the distance between the skull and the mandibulo-maxillary line (D2) were measured and the D1:D2 ratio (PFSR) was calculated. In euploid pregnancies, regression analysis was used to determine the association between D1, D2 and PFSR with gestational age (GA). D1 and D2 were expressed as delta (Δ) values with gestational age. ΔD1, ΔD2 and PFSR in cases and controls were compared. Results: In trisomy-21, compared to controls, ΔD1 was increased (1.417 vs. 0.000 mm, p < 0.0001), ΔD2 was decreased (-0.842 vs. 0.000 mm, p = 0.003) and PFSR was increased (0.753 vs. 0.463, p < 0.0001). At a false-positive rate of 5%, the detection rates in screening by ΔD1, ΔD2 and PSFR were 80.0% (95% CI 65.4-90.4), 46.7% (95% CI 31.7-62.1) and 100.0% (95% CI 92.1-100.0), respectively. Conclusion: The PFSR is an effective marker in second-trimester screening for trisomy-21.

Sphenofrontal distance on three-dimensional ultrasound in euploid and trisomy-21 fetuses at 16-24 weeks' gestation

“…Previous sonographic studies have demonstrated that second‐ and third‐trimester fetuses with trisomy 21 show signs of mid‐facial hypoplasia, which can be assessed by measuring NB length, PT and PFSR. Our results suggest that a contribution to the flat face of fetuses with trisomy 21 is also provided by a shorter sphenofrontal distance, which could be due to dorsal displacement of the lower portion of the frontal bone (Figure ).…”

“…Ultrasound examination of the fetal profile in the second and third trimesters of pregnancy enables the assessment of several facial measurements that are significantly different in fetuses with trisomy 21 from in those that are chromosomally normal. Previous studies have shown that trisomy‐21 fetuses have an increased prevalence of nasal bone absence or hypoplasia, prenasal thickening, wide frontomaxillary facial angle, increased prenasal thickness (PT):nasal bone (NB) length ratio and high prefrontal space ratio (PFSR).…”

Facial markers in second‐ and third‐trimester fetuses with trisomy 18 or 13, triploidy or Turner syndrome

“…In this study, which included 91 fetuses with trisomy 21, approximately 80% of the affected fetuses had a PFSR that was above the 95 th centile. Other study groups have confirmed these promising results.…”

The frontal space measurement in euploid and aneuploid pregnancies at 11–13 weeks' gestation

“…The ratio is below the 5th percentile in about 80% of the fetuses with trisomy 21. Other workgroups have confirmed the good results using the PFSR …”