The nasal bones are present in the majority of fetuses with trisomy 21 in the second trimester. This group of fetuses has a characteristic mid-facial anthropometry (wider maxillary angle) that can be assessed by means of 3D ultrasonography.
Objective: To derive indices describing the shape of the placenta, relationship of cord insertion to its centre and cord coiling in 200 term, singleton pregnancy placentas from an unselected population. Method: 200 consecutive unselected women were recruited with singleton pregnancy at 37-42 Weeks. Digital analysis of the placenta was performed using ''Image J'' (http://rsb.info.nih.gov/ij) software. Measurements were taken of the X and Y placental axes and, those intersecting the cord insertion. From these measurements we derived: Eccentricity index-(range 0-1) describes the shape of the placenta, calculated by a formula in use in astronomical calculations (http://www.cleavebooks.co.uk/scol/callipse.htm). 0 = circular placenta; an elongated placenta has a value close to 1. Cord centrality index (CCI) (range 0-1) describes the distance of umbilical cord insertion from the centre of placenta and is derived by the dividing the distance of cord insertion from the centre by half the longest diameter of the placenta. The closer to 1 the value of CCI; the closer the cord insertion is to the chorionic plate margin. Results: The median placental eccentricity is 0.47 (IQR 0.36-0.57) and median value of CCI is 0.32 (IQR 0.18-0.48). The indices were compared to z-score of birth weight within the range 37-42 weeks and no significant correlation was found. Conclusion: Contrary to received wisdom, the term placenta (chorionic plate) is not typically round, nor is the cord insertion normally at the centre of the placenta. There is no relationship in the term placenta between birth weight z-score and placental eccentricity or cord centrality indices.
Objective: An ARSA is diagnosed when the vessel arises separately from the aortic arch and courses behind the trachea, instead of from the brachiocephalic trunk. It is detected by applying color Doppler at the level of the three-vessel-trachea view. An ARSA is found in approx. 1.5% of the normal population and was described to be more common in fetuses with Trisomy 21. The aim of the present study was to find out the prevalence of this vascular variant in fetuses with Trisomy 21. Patients: In the four years study (2004-2008) fetuses with trisomy 21 between 11 weeks and term and a documented course of the right subclavian artery (RSA) were included in the evaluation. Results: A total of 66 fetuses could be assessed and an ARSA was found in 13 cases (19.6%). The prevalence was the same in the group undergoing 11-14 weeks screening (7/33 = 21%). Conclusions: This study confirms earlier observations on the common finding of an ARSA in fetuses with trisomy 21, but the prevalence is lower than first described. 20% prevalence in trisomy 21 fetuses versus 1,5% in the normal population results in a likelihood ratio of 13× increased risk. This sign can be added to first and second trimester genetic scan. P01.02 Down syndrome screening using first trimester combined tests and conditional use of femur length at routine anomaly scan Objective: To evaluate the performance of contingent use of femur length at routine mid-trimester scan in screening for Down syndrome (DS) in women who had previously undergone first trimester combined screening, with disclosure of risk estimates. Material and methods: This was a simulation study based on the results of a prospective trial of screening for DS using first-trimester combined screening followed by second-trimester ultrasound examination in an unselected population (Rozenberg et al. 2006). Using estimates from the literature, a simulation study was undertaken to evaluate the performance of a contingent screening, based on adding short femur length (FL) at 20-24 weeks as a soft marker in women at intermediate risk on the basis of their first trimester screening results. Sensitivity (Se) and specificity (Spe), detection rates (DR) and false positive rates (FPR) of this contingent use of femur length for the diagnosis of DS were computed. Results: Simulations were computed based on a total of 21,492 patients included. The median maternal age was 30.7 years (range 18.0-46.3). The median gestational age at ultrasound was 12 + 3 weeks (range: 11 + 0; 13 + 6). Contingent screening allowed for an improvement in screening performance. For example, choosing a first trimester risk cutoff of 1/100 and a second trimester risk cutoff of 1/1000 for the use of FL, would allow a Se of 88.4% at a 3% FPR. A first trimester risk cutoff of 1/200 and a second trimester risk cutoff of 1/1000 for the use of FL, would allow a Se of 92.3% at a 4% FPR. Conclusion: This study demonstrates that a sequential screening approach can be used with ultrasound soft markers. Such approach would provide the potential for...
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