Evaluation of pre-test counselling offered for non-invasive prenatal testing (NIPT) as a primary screening tool.

The increasing popularity and expansion of non-invasive prenatal testing (NIPT) to screen for rare conditions beyond common trisomies prompts evaluation of pre-test counselling currently offered. We conducted a prospective survey to assess women's knowledge of NIPT in those who had undergone NIPT (study group) and those who were planning to have NIPT (control group). Out of the 189 questionnaires analysed, the study group did not show a higher knowledge score compared to the control group (P = 0.097). 44% misunderstood that NIPT can identify more conditions than invasive testing, 69.8% were unaware of the recommended need for nuchal translucency measurement and 52.6% were unaware of the possibility of incidental findings. 31% even considered discussing termination of pregnancy as one of the next steps if NIPT shows high risk for Down syndrome. This study shows that current pre-test counselling is inadequate. Service providers should address these knowledge gaps and assist women to make informed choices.Impact StatementWhat is already known on this subject? Pre-test counselling for non-invasive prenatal testing (NIPT) should be conducted to assist women in making an informed consent.What do the results of this study add? Our results show that a significant proportion of women are unaware of the limitations of NIPT.What are the implications of these findings for clinical practice and/or further research? Service providers should improve their pre-test counselling focusing on areas of knowledge deficiencies and misunderstanding on NIPT identified in this study.

Prenatal presentation in two fetuses with features of Beckwith Wiedemann syndrome-An unexpected diagnosis of androgenetic chimera and its clinical implications.

Beckwith Wiedemann Syndrome (BWS, OMIM 130650) is an imprinting disorder that may present antenatally with a constellation of sonographic features namely polyhydramnios, macrosomia, macroglossia, omphalocele, placental mesenchymal dysplasia, cardiomegaly, nephromegaly, fetal hydrops, and other rare anomalies. Paternal uniparental disomy in chromosome 11p15 imprinting region accounts for 20% of all BWS, and 8% among those were due to genome-wide paternal uniparental disomy (GWpUPD). GWpUPD is a rare condition and usually results in prenatal lethality. The 31 liveborns reported in the literature demonstrate female predominance in surviving GWpUPD. Here, we reported two prenatal cases which initially presented with features suggestive of BWS, which subsequently were confirmed to have GWpUPD. Further trio SNP genotyping analysis using SNP-based chromosomal microarray revealed androgenetic biparental chimera as the underlying cause. Finally, we highlighted the importance of recognizing GWpUPD as a possible cause in a fetus presenting with BWS phenotype, as it carried a different disease prognosis, tumor predisposition, manifestations of other imprinting disorders, and possibility in unmasking autosomal recessive disorders from the paternal alleles.

Neonatal outcome and mode of delivery in the presence of nuchal cord loops: implications on patient counselling and the mode of delivery.

PURPOSE: To review and compare the foetal outcomes and mode of delivery in patients with nuchal cord for single loop, double loops, and multiple loops. METHODS: A retrospective study of 4,404 singleton term pregnancies which underwent spontaneous labour was conducted. The patients were classified into five groups: without nuchal cord, nuchal cord of any turns, nuchal cord for 1 turn, nuchal cord for 2 turns and nuchal cord for 3 turns or above. The perinatal outcomes and mode of delivery were then compared. RESULTS: Nuchal cord of any turns was not shown to be associated with intrauterine death, neonatal death, Apgar score <7 at 1 and 5 min. Only nuchal cord for three turns or more were associated with higher incidence of meconium-stained liquor, neonatal unit admission, suspected foetal distress during labour and emergency caesarean section. CONCLUSIONS: Only nuchal cord for 3 turns or more was associated with higher incidence of suspected foetal distress. However, the Apgar scores were not affected. Therefore, nuchal cord of any turns was not associated with adverse foetal outcomes. Prenatal ultrasound scan for nuchal cord is, therefore, unnecessary and there should be no differences in management of nuchal cord of any turns.

Nomogram for fetal limb bones in Chinese ethnicity.

OBJECTIVE: To construct fetal limb bone nomograms in the Chinese ethnic population. METHODS: This was a prospective cross-sectional study on singleton pregnancies between 12 and 37 weeks of gestation. Femur, tibia, fibula, humerus, ulna, radius, and foot length were measured in a standardized manner by one of the three sonographers. Each fetus's measurements were only included once and those who developed maternal or fetal complications were excluded. Fractional polynomial regression model was used to obtain the 3rd, 10th, 50th, 90th, and 97th centiles for each of the limb measurement. Z-score for the 50th centile of each fetal limb measurement was then compared with published nomograms derived from other populations. RESULTS: Of the 843 scans performed, 775 were included in analysis after excluding conditions such as pre-eclampsia, chromosomal abnormalities, single umbilical artery and skeletal dysplasia. Comparison with other populations showed that Chinese had shorter fetal limb bone lengths than the Caucasian and Afro-Caribbean populations. CONCLUSION: This study established nomograms for all the fetal limb bones in the Chinese ethnic population, which showed lengths comparatively shorter than Caucasian and Afro-Caribbean nomograms. This would reduce the false alarm of short fetal limb bone lengths and its consequent anxiety and intervention.

Fetal bradycardia and acidosis during maternal parenteral iron: Case reports and literature review.

Iron deficiency anemia is an important problem among pregnant women, and intravenous (IV) iron infusions have been increasingly used. Whether fetal monitoring is required during infusion has been debated, with a recent guideline by Hematologists recommending against such. We report two cases of fetal bradycardia after iron isomaltoside (IIM), in women with otherwise good maternal and fetal health. Both developed dyspnea with desaturation minutes from infusion, followed by persistent fetal bradycardia. Both underwent category 1 CS, with cord arterial pH of 7.08 and 6.94 respectively. Upon literature review, only three case reports on fetal bradycardia in IV iron were identified. For older IV iron formulations, a case was reported after IV dextran test dose, while two cases after ferric gluconate were reported. For the new formulation IIM, only one case was reported so far, but in a woman with Crohn's disease and intrauterine growth restriction. IV iron in pregnancy carries risk of anaphylactic or hypersensitivity reactions, even with the newest formulations and in women with good maternal and fetal health. While rarely reported so far, fetal bradycardia is a possible consequence, commonly preceded by respiratory symptoms. Fetal monitoring should therefore be considered during infusion.

Secondary findings from non-invasive prenatal testing for common fetal aneuploidies by whole genome sequencing as a clinical service.

OBJECTIVE: To report secondary or additional findings arising from introduction of non-invasive prenatal testing (NIPT) for aneuploidy by whole genome sequencing as a clinical service. METHODS: Five cases with secondary findings were reviewed. RESULTS: In Case 1, NIPT revealed a large duplication in chromosome 18p, which was supported by arrayCGH of amniocyte DNA, with final karyotype showing mosaic tetrasomy 18p. In Case 2, a deletion in the proximal long arm of chromosome 18 of maternal origin was suspected and confirmed by arrayCGH of maternal white cell DNA. In Case 3, NIPT was negative for trisomies 21 and 18. In-depth analysis for deletions/duplications was requested when fetal structural anomalies were detected at routine scan. A deletion in the proximal long arm of chromosome 3 was found and confirmed by karyotyping. In Case 4, NIPT correctly predicted confined placental mosaicism with triple trisomy involving chromosomes X, 7 and 21. In Case 5, NIPT correctly detected a previously unknown maternal mosaicism for 45X. CONCLUSION: Non-invasive prenatal testing is able to detect a wide range of fetal, placental and maternal chromosomal abnormalities. This has important implications on patient counseling when an abnormality is detected by NIPT.

Placental site in the second trimester of pregnancy and its association with subsequent obstetric outcome.

OBJECTIVE: To determine if placental location in the second trimester of pregnancy is associated with adverse pregnancy outcomes. METHODS: We performed a retrospective study on 16 236 patients having ultrasound examination at 14 to 23 weeks of gestation between 2000 and 2007. The placental location was classified into one of four groups: 'central', 'fundal', 'lateral' and 'covering Os'. Obstetric outcomes of non-central placenta were compared to those with 'central' placenta. RESULTS: Women with a 'fundal' placenta were at increased risk of developing pre-eclampsia (PET) (odds ratios (OR) = 2.27; 95% confidence intervals (CI), 1.31-3.93), a preterm delivery before 34 weeks (OR = 2.23; 95% CI, 1.18-4.22), a non-vertex presentation (OR = 3.48; 95% CI, 2.49-4.86), undergoing a manual removal of placenta (MROP) following a vaginal delivery (OR = 7.1; 95% CI, 4.24-11.85) and small for gestational age (SGA) (OR = 1.35; 95% CI, 1.03-1.79). Women with a 'lateral' placenta were at increased risk of developing PET (OR = 2.04; 95% CI, 1.28-3.25), spontaneous preterm delivery before 34 weeks (OR = 2.04; 95% CI, 1.04-3.98), MROP (OR = 6.75; 95% CI, 4.4-10.33) and SGA (OR = 1.82; 95% CI, 1.48-2.23). Five women with a 'cover Os' placenta had an increased risk of postpartum haemorrhage (>1000 mL) (OR = 6.18; 95% CI 2.29-16.65) if they had a vaginal delivery. CONCLUSION: Non-central placental location in the second trimester is associated with an increase risk of adverse obstetric outcome.

First Case Report of Maternal Mosaic Tetrasomy 9p Incidentally Detected on Non-Invasive Prenatal Testing.

Tetrasomy 9p (ORPHA:3390) is a rare syndrome, hallmarked by growth retardation; psychomotor delay; mild to moderate intellectual disability; and a spectrum of skeletal, cardiac, renal and urogenital defects. Here we present a Chinese female with good past health who conceived her pregnancy naturally. Non-invasive prenatal testing (NIPT) showed multiple chromosomal aberrations were consistently detected in two sampling times, which included elevation in DNA from chromosome 9p. Amniocentesis was performed and sent for chromosomal microarray, which was normal. Maternal karyotype revealed that mos 47,XX,+dic(9;9)(q21.1;q21.1)(24)/46,XX(9) presents mosaic tetrasomy for the short arm of chromosome 9p and is related to the NIPT results showing elevation in DNA from chromosome 9p. The pregnancy was uneventful, and the patient was delivered at term. Maternal samples were obtained at two different time points after delivery showed the same multiple chromosomal aberrations detected during pregnancy. This is a first report on an unusual case of mosaic isodicentric tetrasomy 9p in a healthy adult with normal intellect. With widespread adoption of NIPT for screening fetal aneuploidy and genome-wide copy number changes, a rise in incidental detection of maternal rare genetic syndrome will bring challenges in our current approach to genetic counselling and prenatal diagnosis.

Massive subchorionic thrombohematoma: a series of 10 cases.

A retrospective audit identified 10 cases of massive idiopathic subchorionic thrombohematoma. The incidence was 1:3,133. Only six of these pregnancies resulted in a livebirth and only two reached term. In eight cases there were ultrasound abnormalities, including two cases of placentomegaly both of which resulted in a pregnancy loss. There was one placental abruption. Seven of the women were nulliparous. Massive subchorionic thrombohematoma is associated with poor pregnancy outcome. Ultrasound findings of placentomegaly might be a bad prognostic sign.

Nausea and vomiting in health-related quality of life among Chinese pregnant women.

BACKGROUND: Nausea and vomiting in pregnancy (NVP) is the most common pregnancy complication affecting women during the first trimester of pregnancy. The cause of NVP remains unknown and factors associated with the occurrence of NVP are contradictory. There is currently little information on its effects of NVP in general and specifically in the Chinese population. AIMS: To assess the prevalence of NVP with different degree of severity and identify their relationship with health-related quality of life (HRQoL) and to determine its association with the sociodemographic and obstetric factors. METHODS: In a prospective cross-sectional study, 396 women who attended the antenatal clinic between 10 and 14 weeks of gestation were invited to complete a structured questionnaire covering maternal characteristics, severity of NVP and their HRQoL. The status of NVP and HRQoL was measured by the frequency of symptoms and the Medical Outcomes Study Short-Form-36 (SF-36) respectively. Logistic regression analysis was performed to delineate the factors associated with NVP. RESULTS: The prevalence of NVP was 90.9%. Almost all domains and dimensions of SF-36 were affected by the presence of NVP and its severity. Factors associated with the presence and severity of NVP were non-smoking, younger age and history of NVP in previous pregnancy. CONCLUSIONS: The various degrees of severity of NVP significantly impair both physical and mental HRQoL in Hong Kong Chinese women. Awareness and care should be given to women with symptoms of nausea or retching alone, as well as vomiting.

First trimester measurements of nasal bone length using three-dimensional ultrasound.

OBJECTIVES: To investigate the feasibility and reproducibility of measurements of nasal bone length using a three-dimensional (3D) ultrasound in the first trimester. METHODS: In a prospective study, 118 consecutive pregnant women attending for Down syndrome screening at 11-13 + 6 weeks were recruited. They had successful fetal nasal bone measurement by two-dimensional (2D) ultrasound by four operators. Three-dimensional volumes were recorded in the mid-sagittal plane of fetal profile by the fifth operator and examined using multiplanar techniques. Another independent investigator randomly compared his measurements with one of the four operators. RESULTS: In the subsequent 3D examination, the nasal bone length could be examined in 94 cases (79.7%). The mean difference between the 2D and 3D measurements was 0.19 mm [95% confidence interval (CI) 0.08 to 0.31] (P < 0.05). Limits of agreement were -0.73 to 1.11. The mean differences between these two observers were 0.66 mm (95% CI -0.47 to 0.86) (P < 0.05). CONCLUSIONS: There was significant intermethod difference between the results obtained by 2D and 3D, as well as substantial interobserver variation in 3D measurement of fetal nasal bone length in the first trimester. Independent 3D measurement of nasal bone offers no additional advantages over 2D sonography.

Study on the applicability of frontomaxillary facial angle in the first-trimester trisomy 21 fetuses in Chinese population.

OBJECTIVE: To evaluate the measurement of frontomaxillary facial (FMF) angle at 11 weeks to 13 weeks, 6 days in a Chinese population and its applicability in the screening for fetal trisomy 21. METHOD: In a retrospective study, the stored images for the measurement of fetal nuchal translucency (NT) thickness in a Chinese population from August 2003 to March 2007 were reviewed for the comparison of the FMF angle between 22 trisomy 21 fetuses (study group) with 220 randomly selected normal fetuses with satisfactory images (control group). RESULTS: No association between FMF angle and NT, nasal bone length, or fetal heart rate was shown (P > 0.05). But the FMF angle was significantly greater in the trisomy 21 fetuses (89.7 vs 82.8, P < 0.001). The intraobserver and interobserver agreement were assessed in 9.5% (n = 21) normal cases. Mean (SD) differences of two observers were -0.83 (2.69) degrees (P > 0.05). For each observer, mean (SD) differences between the two paired measurements were -0.98 (3.11) degrees and 0.93 (1.80) degrees , respectively (P > 0.05). CONCLUSION: Our results indicated that measurement of the FMF angle in the first trimester can be incorporated into the screening of trisomy 21 in the Chinese population, and its application is not affected by intraobserver and interobserver variability.

Ultrasound screening for fetal structural abnormalities performed by trained midwives in the second trimester in a low-risk population--an appraisal.

OBJECTIVE: To determine the performance of trained midwives in second trimester ultrasound screening for fetal structural abnormalities in a low-risk population. DESIGN: Retrospective study. SETTING: University Department of Obstetrics and Gynecology. POPULATION: About 13,882 women with singleton pregnancies. METHODS: The findings of routine second trimester anomaly scan performed by midwives were reviewed. Reasons for referral to maternal fetal medicine (MFM) specialists for further assessment were analyzed. MAIN OUTCOME MEASURES: The detection, false positive and false alarm rates for fetal anomalies. RESULTS: One hundred and eighty-nine pregnancies with unknown outcome were excluded from the final analysis. Overall, 617 (4.51%) women were referred to MFM specialists for further assessment, of which 470 (70.2%) were for soft markers alone and 147 (23.8%) for suspected fetal structural abnormalities. In these 13,693 fetuses with known outcome, malformed fetuses were present in 185, a prevalence of 1.35%. Of these, 115 were detected during the second trimester scan and two were detected in the third trimester. The remaining 68 malformed fetuses, most of which had minor anomalies, were identified after birth. The detection rate for a malformed fetus in second trimester scan was 62.2% (115/185) (95% CI 55.2-69.2). There were four cases of false positives and 33 cases of false alarm. CONCLUSIONS: Experienced midwives with proper training can detect the majority of major structural abnormalities. Continuous audit and quality control plays a significant role in optimizing the fetal structural examination.

Gastroschisis associated with an intra-abdominal umbilical vein varix: a report of 2 cases.

We describe 2 cases of gastroschisis which were found to be associated with an intra-abdominal umbilical vein varix.

Fetal nasal bone status in Chinese women undergoing first-trimester screening for trisomy 21.

OBJECTIVE: The objective of the study was to determine the likelihood ratio for trisomy 21 in Chinese fetuses with absent nasal bone (NB) at 11-14 weeks of gestation. STUDY DESIGN: The NB was classified as present or absent in 8101 chromosomally/phenotypically normal or trisomy 21 pregnancies. The effect of crown rump length (CRL), nuchal translucency (NT), maternal age, and fetal karyotype on the incidence of absent NB was examined using logistic regression. RESULTS: The NB was successfully examined in 7925 cases (97.8%). The incidence of absent NB in unaffected and trisomy 21 cases were 2.1% (164/7899) and 50% (13/26), respectively. CRL (odds ratio [OR], 0.9; 95% confidence interval [CI], 0.87-0.92), NT (OR, 1.7; 95% CI, 1.4-2.3), and trisomy 21 (OR, 22.3; 95% CI, 8.1-61) were significant independent predictors of likelihood of absent NB. Positive likelihood ratios (LR) for trisomy 21 in Chinese were lower than that of Caucasians for the equivalent CRL and NT measurements. CONCLUSION: Estimated risk for trisomy 21 in Chinese incorporating nasal bone status should use LRs derived in Chinese rather than Caucasians.

Fetal anaemia as a cause of fetal injury: diagnosis and management.

PURPOSE OF REVIEW: This review provides up-to-date information on the diagnosis and management of fetal anaemia. RECENT FINDINGS: Exciting advances in the field of red blood cell isoimmunization are phasing out the need for invasive procedures. Rhesus blood group genotyping using fetal DNA in maternal plasma has been introduced into clinical practice with remarkable success. The role of middle cerebral artery peak systolic velocity in screening for fetal anaemia has been confirmed in various causes of fetal anaemia. A recent review of a successful Iran national screening programme for thalassaemia provided a timely and valuable educational opportunity. The value of intrauterine transfusion as a treatment for fetal anaemia was demonstrated by both high success rate and low procedure-related pregnancy loss rate. SUMMARY: Fetal anaemia is one of the severe fetal conditions that affect the worldwide population. Rhesus isoimmunization remains an important health issue despite the recommendation for anti-D immunoglobulin prophylaxis and injection after sensitizing events. Noninvasive ultrasound diagnostic methods have replaced traditional invasive procedures in the assessment of fetus at risk of anaemia due to various causes, including red blood cell isoimmunization, parvovirus B19 infection and thalassaemia. The increased availability of intrauterine transfusion will help to improve the prognosis of these anaemic fetuses.

[Outcome of 1,355 consecutive transabdominal chorionic villus samplings in 1,351 patients].

BACKGROUND: The true risk of chronic villus sampling (CVS) is poorly defined. The objective of this study was to review the clinical outcome of transabdominal CVS performed in a university teaching unit, with an emphasis on the complication rate. METHODS: A comprehensive audit database was maintained for 1,351 pregnant women, including 17 sets of twin pregnancies, who had a CVS. Details and outcome of all CVSs made in the unit between May 1996 and May 2004 were reviewed. All CVSs were performed by one of 5 operators using the identical techniques. RESULTS: All procedures were performed transabdominally. A total of 1,355 CVSs were performed because there were 4 dichorionic twin pregnancies which required 2 punctures. The mean gestation at CVS was (11.8 +/- 0.7) weeks, and 97.3% of the procedures were performed between 11 and 13 completed weeks. The majority (96.2%) required only 1 puncture to achieve correct needle placement. The procedure failed to obtain an adequate sample in 4 subjects (0.30%). A total of 1,351 chromosomal studies were requested and there was 1 case (0.07%) of culture failure. The results of chromosomal studies were available within 14 days in 36.7% of the cases and within 21 days in 94.0%. Overall, 77 chromosomal abnormalities (5.7%) and 5 cases of thalassemia major were detected. Pregnancy outcome was unknown in only 13 singleton subjects (0.96%). In the remaining 1,355 fetuses, there were 76 pregnancy terminations (5.56%), 10 fetal losses with obvious obstetric causes (0.73%), and 21 potentially procedure-related fetal losses (1.54%). In the last group, the majority had one or more co-existing obstetric complications. The background fetal loss rate for pregnancies at similar gestational age in the unit was about 0.8%. Therefore, the procedure-related fetal loss rate was estimated to be at the maximum of 0.74%. CONCLUSIONS: In experienced hands, first trimester transabdominal CVS is an accurate and safe invasive prenatal diagnostic procedure. It should be one of the treatment options available to pregnant women who require prenatal genetic diagnosis.

Prediction of successful vaginal delivery in women undergoing external cephalic version at term for breech presentation.

OBJECTIVE: The aim of this study is to evaluate the clinical and sonographic predictors of ultimate successful vaginal delivery in women undergoing external cephalic version. STUDY DESIGN: The study population consisted of women with external cephalic version performed at or after 36 weeks of gestation. They were randomized into group A or B, each consisted of half of the total study population. Logistic regression was performed on group A to identify the significant independent variables in predicting successful cephalic vaginal delivery, which were used to construct a prediction model. The derived regression model was then tested in group B to assess its accuracy. RESULTS: The study included 407 pregnancies. Maternal weight (kg) at the time of version, maternal height (cm), multiparity, engagement of fetal presenting part, and fetal head palpable were significant independent variables of successful version and vaginal delivery (regression coefficients are: -0.084, 0.085, 1.752, -1.271, and 0.725, respectively). A prediction model was constructed based on these independent variables. The weighted average of the overall accuracy in predicting success or failure of version and vaginal delivery was 70.9%. The regression model was then applied to study group B. Using 0.50 as the cutoff value, the sensitivity, specificity, positive, and negative predictive values were 75.4, 58.8, 73.7, and 61.0%, respectively. CONCLUSION: A regression model constructed based on clinical variables failed to provide an accurate predictive tool of successful external cephalic version and vaginal delivery. However, in women who are equivocal about external cephalic version, a high prediction of success would be encouraging.

Scan the fetal heart by real-time three-dimensional echocardiography with live xPlane imaging.

OBJECTIVE: To describe the methodology of live xPlane imaging in the visualization of the fetal heart in detail. METHODS: Fifty-one consecutive pregnant women with singleton pregnancies were imaged to display four screening sections of the fetal heart, the four-chamber view, the left outflow tract view (LVOT), the right outflow tract view (RVOT), and the three-vessel and trachea view (3VT), using live xPlane imaging. The methodology of how to visualize the screening planes was described in detail. We used two methods to image the fetal heart with live xPlane imaging: one uses the four-chamber view as the starting plane and the other uses the longitudinal view of fetal upper thorax as the starting plane. RESULTS: When using the four-chamber view as the starting plane, the visualization rate of LVOT, RVOT, and 3VT was 94.1% (48/51), 100% (51/51), and 98.0% (50/51), respectively. When using the longitudinal view as the starting plane, the visualization rate of four-chamber view, LVOT, RVOT, and 3VT was 100% (51/51), 100% (51/51), 41.2% (21/51), and 100% (51/51), respectively. CONCLUSIONS: Live xPlane imaging can be used to visualize the screening views of the fetal heart, and potentially may be a useful tool for the assessment and diagnosis of fetal congenital heart diseases.

Assessment of sonographer nuchal translucency measurement performance--central tendency and dispersion.

OBJECTIVE: To assess center and sonographer nuchal translucency (NT) measurements that were performed as part of routine prenatal screening for Down syndrome. METHODS: Sonographers were assessed for measures of central tendency and dispersion by comparing them with expected population median and dispersion parameters. NT measurements were converted to multiples of the expected NT values according to CRL (NTMoM) and transformed to their log(10) equivalent (log(10) NTMoM). Central tendency and measurement were assessed by checking whether the median of the NTMoM distribution and SD of the log(10) NTMoM distributions were, respectively, within 5% or 10% of the expected median of 1 and SD of 0.1. Assessment was performed using both the Center specific and Fetal Medicine Foundation (FMF) reference NT for Crown rump length (CRL). RESULTS: The median NT MoM was 0.95 MoM using the FMF reference and 1.01 MoM when assessed using our center specific reference median. The difference between the center and FMF derived NT MoMs was statistically significantly (p < 0.0001). NTMoM medians increased over time at a rate of 0.0099 MoM per year while log(10) NT MoM measurement dispersement was similar to the 0.1 value expected and decreased by 0.0048 per year. CONCLUSION: Centers should routinely monitor the quality of NT measurements used to estimate Down syndrome screening risk and should provide individualized feedback to sonographers of their measures of central tendency and dispersion to ensure consistent and improved performance. NT reference medians adopted from other populations should be assessed and validated against a centers own measurement distribution.