Improved Constraints on Primordial Gravitational Waves using Planck, WMAP, and BICEP/Keck Observations through the 2018 Observing Season.

We present results from an analysis of all data taken by the BICEP2, Keck Array, and BICEP3 CMB polarization experiments up to and including the 2018 observing season. We add additional Keck Array observations at 220 GHz and BICEP3 observations at 95 GHz to the previous 95/150/220 GHz dataset. The Q/U maps now reach depths of 2.8, 2.8, and 8.8 µK_{CMB} arcmin at 95, 150, and 220 GHz, respectively, over an effective area of ≈600 square degrees at 95 GHz and ≈400 square degrees at 150 and 220 GHz. The 220 GHz maps now achieve a signal-to-noise ratio on polarized dust emission exceeding that of Planck at 353 GHz. We take auto- and cross-spectra between these maps and publicly available WMAP and Planck maps at frequencies from 23 to 353 GHz and evaluate the joint likelihood of the spectra versus a multicomponent model of lensed ΛCDM+r+dust+synchrotron+noise. The foreground model has seven parameters, and no longer requires a prior on the frequency spectral index of the dust emission taken from measurements on other regions of the sky. This model is an adequate description of the data at the current noise levels. The likelihood analysis yields the constraint r_{0.05}<0.036 at 95% confidence. Running maximum likelihood search on simulations we obtain unbiased results and find that σ(r)=0.009. These are the strongest constraints to date on primordial gravitational waves.

Internal Delensing of Cosmic Microwave Background Polarization B-Modes with the POLARBEAR Experiment.

Using only cosmic microwave background polarization data from the polarbear experiment, we measure B-mode polarization delensing on subdegree scales at more than 5σ significance. We achieve a 14% B-mode power variance reduction, the highest to date for internal delensing, and improve this result to 22% by applying for the first time an iterative maximum a posteriori delensing method. Our analysis demonstrates the capability of internal delensing as a means of improving constraints on inflationary models, paving the way for the optimal analysis of next-generation primordial B-mode experiments.

Infrared spectra of primary melanomas can predict response to chemotherapy: The example of dacarbazine.

Metastatic melanomas are highly aggressive and median survival is 6-9months for stage IV patients in the absence of treatment with anti-tumor activity. Dacarbazine is an alkylating agent that has been widely used in the treatment of metastatic melanomas and that could be still used in combination with targeted or immune therapies. Indeed, therapeutic benefits of these treatments in monotherapy are poor and one option to improve them is to combine drugs and/or to better anticipate the individual response to a defined treatment. To our best knowledge and to date, there is no test available to predict the response of a patient to dacarbazine. We show here that examination of melanoma histological sections by infrared micro-spectroscopy reveals the sensitivity of the cancer to dacarbazine. Unsupervised analysis of the FTIR spectra evidences spontaneous and significant clustering of infrared spectra into two groups that match the clinical responsiveness of the patients to dacarbazine used as a first-line treatment. A supervised model resulted in 83% of the patient status (responder/non-responder) being correctly identified. The spectra revealed a key modification in the nature and quantity of lipids in the cells of both groups.

Identification of melanoma cells and lymphocyte subpopulations in lymph node metastases by FTIR imaging histopathology.

While early stages of melanoma are usually cured by surgery, metastatic melanomas are difficult to treat because the widely available options have low response rates. Careful and precise diagnosis and staging are essential to determine patient's risk and to select appropriate treatments. Fortunately, the recent progress in immunotherapy is very encouraging. In this context, it is important to characterize the intratumoral infiltration of immune cells in each patient, which is however not done routinely due to the lack of standardized methods. In this study, we used Fourier transform infrared (FTIR) imaging combined with multivariate statistical analyses to investigate non-metastatic and metastatic lymph nodes from melanoma patients. Our results show that the different cell types have different infrared spectral features allowing automated identification of these cell types. High recognition rates were obtained using a supervised partial least square discriminant analysis (PLS-DA) model. Melanoma cells were recognized with 87.1% sensitivity and 85.7% specificity, showing that FTIR spectroscopy has similar detection power as immunohistochemistry. Besides, FTIR imaging could also distinguish lymphocyte subpopulations (B and T cells). Finally, we investigated the changes in lymphocytes due to the presence of metastases. Interestingly, specific features of spectra of lymphocytes present in metastatic or tumor-free lymph nodes could be evidenced by PCA. A PLS-DA model was capable of predicting whether lymphocytes originated from invaded or non-invaded lymph nodes. These data demonstrate that FTIR imaging is capable to distinguish known and also novel biological features in human tissues, with potential practical relevance for histopathological diagnosis and biomarker assessment.

Mortality from aortic stenosis: prospective study of serum calcium and phosphate.

PURPOSE: To investigate the associations between levels of serum calcium and phosphate and subsequent death from aortic stenosis, and the implications for prevention. METHODS: A prospective (nested case-control) analysis of serum calcium and phosphate levels was performed in stored samples from the British United Provident Association prospective study of 21 520 men aged 35-64, followed for up to 32 years. There were 49 men without baseline valvular heart disease who subsequently died of aortic stenosis. Each was matched, for age, duration of sample storage and number of freeze-thaw cycles, with four unaffected control subjects. Odds ratios for death from aortic stenosis were estimated by logistic regression. RESULTS: Mean serum calcium concentration was higher in men who died of aortic stenosis than in those who did not (2.44 vs. 2.39 mmol L-1 ; P = 0.01). The risk of death from aortic stenosis in the highest calcium tertile was 2.87-fold higher than in the lowest tertile (95% confidence interval 1.22-6.76). There was a continuous dose-response relationship; risk of death from aortic stenosis increased by 51% (11-105%) per 0.1 mmol L-1 increase in serum calcium, equivalent to a 34% (10-52%) lower risk per 0.1 mmol L-1 decrease. Serum phosphate was not significantly higher in men who died of aortic stenosis than in those who did not (1.0 vs. 0.99 mmol L-1 ; P = 0.76). CONCLUSIONS: The association between serum calcium and subsequent mortality from aortic stenosis is of potential preventive significance. If confirmed quantitatively in other similar cohort studies, the results suggest that a very small reduction in serum calcium (about 5%) could translate into a large (about one-third) reduction in aortic stenosis.

UK Lung Cancer RCT Pilot Screening Trial: baseline findings from the screening arm provide evidence for the potential implementation of lung cancer screening.

BACKGROUND: Lung cancer screening using low-dose CT (LDCT) was shown to reduce lung cancer mortality by 20% in the National Lung Screening Trial. METHODS: The pilot UK Lung Cancer Screening (UKLS) is a randomised controlled trial of LDCT screening for lung cancer versus usual care. A population-based questionnaire was used to identify high-risk individuals. CT screen-detected nodules were managed by a pre-specified protocol. Cost effectiveness was modelled with reference to the National Lung Cancer Screening Trial mortality reduction. RESULTS: 247 354 individuals aged 50-75 years were approached; 30.7% expressed an interest, 8729 (11.5%) were eligible and 4055 were randomised, 2028 into the CT arm (1994 underwent a CT). Forty-two participants (2.1%) had confirmed lung cancer, 34 (1.7%) at baseline and 8 (0.4%) at the 12-month scan. 28/42 (66.7%) had stage I disease, 36/42 (85.7%) had stage I or II disease. 35/42 (83.3%) had surgical resection. 536 subjects had nodules greater than 50 mm(3) or 5 mm diameter and 41/536 were found to have lung cancer. One further cancer was detected by follow-up of nodules between 15 and 50 mm(3) at 12 months. The baseline estimate for the incremental cost-effectiveness ratio of once-only CT screening, under the UKLS protocol, was £8466 per quality adjusted life year gained (CI £5542 to £12 569). CONCLUSIONS: The UKLS pilot trial demonstrated that it is possible to detect lung cancer at an early stage and deliver potentially curative treatment in over 80% of cases. Health economic analysis suggests that the intervention would be cost effective-this needs to be confirmed using data on observed lung cancer mortality reduction. TRIAL REGISTRATION: ISRCTN 78513845.

Infrared imaging of primary melanomas reveals hints of regional and distant metastases.

Melanoma is the deadliest form of skin cancer. Metastatic melanomas are resistant to almost all existing adjuvant therapies such as chemotherapy and radiotherapy, so detection of metastases remains a challenge, and no biomarkers are currently available to detect primary tumors with the highest risk of metastasis. Results presented in this paper show that Fourier Transform Infrared (FTIR) imaging of histological sections followed by supervised partial least squares discriminant analysis (PLS-DA) can accurately (>90%) identify the main cell types commonly found in melanoma tumors. Here we define six cell types: melanoma cells, erythrocytes, connective tissue (includes blood vessel walls, dermis and collagen regions), keratinocytes, lymphocytes and necrotic cells. Interestingly, more than 98% of the melanoma cells are correctly identified. The spectra of the cells identified as melanomas were then further analyzed. First, we compared melanoma cells in primary tumors (from 26 patients) with melanoma cells from metastases (from 25 patients). Neither supervised nor unsupervised analyses revealed any significant difference. Similarly, we found no significant correlation between the infrared spectra of melanoma cells and the number of proliferative cells assessed by Ki67 immunostaining. Finally, we compared the infrared spectra of primary tumors from patients diagnosed at different stages of the disease. Infrared spectroscopy was capable of pointing out differences between primary tumors of patients at stage I or II and patients at stage III or IV, even by unsupervised analysis. We then developed a supervised PLS-DA model capable of predicting whether tumor cells belonged to one of the two aggregated disease stage groups. The model predicted a high rate of true positives (sensitivity of 88.9%) and a good rate of true negatives (specificity of 70.6%) in external validation. These results demonstrate that infrared spectroscopy can be used to help identify melanoma characteristics related to the cells' invasive capability.

An infrared spectral signature of human lymphocyte subpopulations from peripheral blood.

Metastatic melanomas are frequently refractory to most adjuvant therapies such as chemotherapies and radiotherapies. Recently, immunotherapies have shown good results in the treatment of some metastatic melanomas. Immune cell infiltration in the tumor has been associated with successful immunotherapy. More generally, tumor infiltrating lymphocytes (TILs) in the primary tumor and in metastases of melanoma patients have been demonstrated to correlate positively with favorable clinical outcomes. Altogether, these findings suggest the importance of being able to identify, quantify and characterize immune infiltration at the tumor site for a better diagnostic and treatment choice. In this paper, we used Fourier Transform Infrared (FTIR) imaging to identify and quantify different subpopulations of T cells: the cytotoxic T cells (CD8+), the helper T cells (CD4+) and the regulatory T cells (T reg). As a proof of concept, we investigated pure populations isolated from human peripheral blood from 6 healthy donors. These subpopulations were isolated from blood samples by magnetic labeling and purities were assessed by Fluorescence Activated Cell Sorting (FACS). The results presented here show that Fourier Transform Infrared (FTIR) imaging followed by supervised Partial Least Square Discriminant Analysis (PLS-DA) allows an accurate identification of CD4+ T cells and CD8+ T cells (>86%). We then developed a PLS regression allowing the quantification of T reg in a different mix of immune cells (e.g. Peripheral Blood Mononuclear Cells (PBMCs)). Altogether, these results demonstrate the sensitivity of infrared imaging to detect the low biological variability observed in T cell subpopulations.

Breast cancer and melanoma cell line identification by FTIR imaging after formalin-fixation and paraffin-embedding.

Over the past few decades, Fourier transform infrared (FTIR) spectroscopy coupled to microscopy has been recognized as an emerging and potentially powerful tool in cancer research and diagnosis. For this purpose, histological analyses performed by pathologists are mostly carried out on biopsied tissue that undergoes the formalin-fixation and paraffin-embedding (FFPE) procedure. This processing method ensures an optimal and permanent preservation of the samples, making FFPE-archived tissue an extremely valuable source for retrospective studies. Nevertheless, as highlighted by previous studies, this fixation procedure significantly changes the principal constituents of cells, resulting in important effects on their infrared (IR) spectrum. Despite the chemical and spectral influence of FFPE processing, some studies demonstrate that FTIR imaging allows precise identification of the different cell types present in biopsied tissue, indicating that the FFPE process preserves spectral differences between distinct cell types. In this study, we investigated whether this is also the case for closely related cell lines. We analyzed spectra from 8 cancerous epithelial cell lines: 4 breast cancer cell lines and 4 melanoma cell lines. For each cell line, we harvested cells at subconfluence and divided them into two sets. We first tested the "original" capability of FTIR imaging to identify these closely related cell lines on cells just dried on BaF2 slides. We then repeated the test after submitting the cells to the FFPE procedure. Our results show that the IR spectra of FFPE processed cancerous cell lines undergo small but significant changes due to the treatment. The spectral modifications were interpreted as a potential decrease in the phospholipid content and protein denaturation, in line with the scientific literature on the topic. Nevertheless, unsupervised analyses showed that spectral proximities and distances between closely related cell lines were mostly, but not entirely, conserved after FFPE processing. Finally, PLS-DA statistical analyses highlighted that closely related cell lines are still successfully identified and efficiently distinguished by FTIR spectroscopy after FFPE treatment. This last result paves the way towards identification and characterization of cellular subtypes on FFPE tissue sections by FTIR imaging, indicating that this analysis technique could become a potential useful tool in cancer research.

UK Lung Screen (UKLS) nodule management protocol: modelling of a single screen randomised controlled trial of low-dose CT screening for lung cancer.

The UK Lung Screen (UKLS) is a randomised controlled trial of the use of low-dose multidetector CT for lung cancer screening. It completed the Health Technology Appraisal (HTA)-funded feasibility stage in October 2009 and the pilot UKLS will be initiated in early 2011. The pilot will randomise 4000 subjects to either low-dose CT screening or no screening. The full study, due to start in September 2012, if progression criteria are met, will randomise a further 28,000 subjects from seven centres in the UK. Subjects will be selected if they have sufficient risk of developing lung cancer according to the Liverpool Lung Project risk model. The UKLS employs the 'Wald Single Screen Design', which was modelled in the UKLS feasibility study. This paper describes the modelling of nodule management in UKLS by using volumetric analysis with a single initial screen design and follow-up period of 10 years. This modelling has resulted in the development and adoption of the UKLS care pathway, which will be implemented in the planned CT screening trial in the UK.

Search for a new gauge boson in electron-nucleus fixed-target scattering by the APEX experiment.

We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.

Antenatal screening for Down's syndrome using the Integrated test at two London hospitals.

We carried out an audit of antenatal screening for Down's syndrome using the Integrated test (which provides a single screening result from information collected in the late first and early second trimesters of pregnancy) which was introduced into routine antenatal care at two London hospitals, University College Hospital (UCH) and St Mary's Hospital, in 2003-4. The audit was based on 15,888 women who accepted screening and booked in the first trimester. The Down's syndrome detection rate was 87% (95% confidence interval [CI], 74-95) consistent with an expected detection rate of 89% based on applying the estimates of screening performance of the Serum, Urine and Ultrasound Screening Study (SURUSS) to the maternal age distribution of women who were screened at UCH and St Mary's. The observed false-positive rate was 2.1% (95% CI, 1.9-2.3), compared with an expected of 2.5% for women of the same age. An audit trail (conducted at UCH) indicated that 98% (10,746/10,961) of women accepted integrated screening (2% having a first trimester test) and of these, 94% (10,116) completed both stages of the test. The audit demonstrated that it is feasible to conduct integrated screening within the NHS with a high acceptance rate and a screening performance consistent with that determined from previous research studies.

The POLARBEAR Fourier transform spectrometer calibrator and spectroscopic characterization of the POLARBEAR instrument.

We describe the Fourier Transform Spectrometer (FTS) used for in-field testing of the POLARBEAR receiver, an experiment located in the Atacama Desert of Chile which measures the cosmic microwave background (CMB) polarization. The POLARBEAR-FTS (PB-FTS) is a Martin-Puplett interferometer designed to couple to the Huan Tran Telescope (HTT) on which the POLARBEAR receiver is installed. The PB-FTS measured the spectral response of the POLARBEAR receiver with signal-to-noise ratio >20 for ∼69% of the focal plane detectors due to three features: a high throughput of 15.1 sr cm2, optimized optical coupling to the POLARBEAR optics using a custom designed output parabolic mirror, and a continuously modulated output polarizer. The PB-FTS parabolic mirror is designed to mimic the shape of the 2.5 m-diameter HTT primary reflector, which allows for optimum optical coupling to the POLARBEAR receiver, reducing aberrations and systematics. One polarizing grid is placed at the output of the PB-FTS and modulated via continuous rotation. This modulation allows for decomposition of the signal into different harmonics that can be used to probe potentially pernicious sources of systematic error in a polarization-sensitive instrument. The high throughput and continuous output polarizer modulation features are unique compared to other FTS calibrators used in the CMB field. In-field characterization of the POLARBEAR receiver was accomplished using the PB-FTS in April 2014. We discuss the design, construction, and operation of the PB-FTS and present the spectral characterization of the POLARBEAR receiver. We introduce future applications for the PB-FTS in the next-generation CMB experiment, the Simons Array.

Multiple-marker screening for Down's syndrome: a method of assessing the statistical robustness of proposed tests.

OBJECTIVES: Antenatal screening for Down's syndrome relies on the use of multiple markers in combination. Markers that are highly correlated can cause statistical instability. We used the maximum variance inflation factor (VIF(max)) to determine whether a screening test using multiple markers was robust to imprecision in the estimation of the marker distribution parameters. METHODS: The VIF(max) for a specified screening test was calculated from the correlations between markers in Down's syndrome pregnancies for six tests: integrated and serum integrated tests without repeat measurements, both tests with repeat measurements across trimesters analysed in the standard way, and both tests with repeat measurements analysed as cross-trimester (CT) marker ratios. The screening performance of each test using published parameter values, in terms of the false-negative rates for a 3% false-positive rate (FN(3)), were calculated for simulated populations with medians 0.2 standard deviations (SD) higher or lower than the published values (to reflect imprecision in parameter estimation) for pregnancy-associated plasma protein A and unconjugated oestriol in affected pregnancies. For each test, the VIF(max) value was compared with the coefficient of variation of the FN(3) (FN(3) CV). An independent set of 27 Down's syndrome pregnancies was used to determine how many had meaningless low risks (<1 in 10,000) with each test. RESULTS: Tests with VIF(max) values greater than 5 had FN(3)CV values over 50%, but those with VIF(max) values less than 5 had FN(3) CV values less than 21%. The numbers of Down's syndrome pregnancies with meaningless low risk estimates in the independent set were 18 (64%) in tests with VIF(max) values > or =5 and none for those with values <5. CONCLUSION: VIF(max) values of 5 or more suggest instability. The tests using CT marker ratios were stable (VIF(max) < 3), but the tests using repeat measurements in the standard manner were not (VIF(max) > 5).

Pregnancy-associated plasma protein-A truncation limits in antenatal screening for trisomy 18.

Upper and lower truncation limits are commonly applied to quantitative markers used in medical screening tests. We here examine data on 375 trisomy 18 and 522,081 unaffected singleton pregnancies, to determine if the lower truncation limit should be set below the previously specified 0.2 multiples of the median. A lower truncation limit of 0.15 would reduce the underestimation of the risk of having a trisomy 18 pregnancy in about 50% of affected pregnancies and would lead to an estimated 10 percentage point increase in the detection rate, with only a very small increase in the false-positive rate.

The effect of correlations between screening markers on screening performance.

OBJECTIVES: It is widely thought that correlations between screening markers will tend to degrade screening performance. We performed a computer simulation study to investigate the quantitative effect of correlations between two markers on screening performance, using prenatal screening for Down's syndrome as an example, although the results apply generally. METHODS: Monte Carlo simulation was used to generate values of two hypothetical markers, A and B, in 1000 affected and 1000 unaffected pregnancies. The means, standard deviations and correlations of A and B were varied in five different examples. RESULTS: If markers A and B are, on average, higher in affected than unaffected pregnancies and each marker, individually, has the same detection rate for a given false-positive rate (i.e. the same screening performance), then the screening performance of A and B together tends to decrease as A and B become more positively correlated with each other (within affected or unaffected categories) and tends to increase as A and B become more negatively correlated. If A is, on average, higher in affected pregnancies and B is, on average, lower in affected pregnancies (but again each marker has the same screening performance), the opposite pattern is observed; screening performance increases as A and B become more positively correlated and screening performance decreases as they become more negatively correlated. If A and B have unequal screening performances, modest correlations between A and B have little effect on the screening performance of A and B together, but when the correlations are strong whether positive or negative (with r values greater than about 0.45 or less than -0.45) screening performance progressively increases. CONCLUSION: Correlations between screening markers considered separately in affected and unaffected pregnancies can either decrease or increase screening performance. In practice, these effects are usually modest, because most screening markers are not highly correlated with each other and the effects become important only with strong correlations, whether positive or negative.

Prevalence of neural tube defect pregnancies in England and Wales from 1964 to 2004.

OBJECTIVES: To determine the prevalence of pregnancies with a neural tube defect (NTD) in England and Wales between 1964 and 2004 and to estimate the relative impact of antenatal screening and a change in the incidence of these defects on the prevalence of births with NTDs. SETTINGS: Use of data published by the Office for National Statistics (ONS) on terminations of pregnancies with an NTD and births with an NTD from 1964 to 2004. METHODS: Estimates were made of the total number of terminations of pregnancies and births with an NTD by taking account of the under-reporting of these terminations and births using a previously described method. In 1995 ONS started to report the number of terminations with an NTD rather than the total numbers of terminations with a central nervous system (CNS) malformation that had previously been used to estimate the number of NTD terminations. Adjustment was made for this and new estimates of the total number of NTD pregnancies were produced to 2004. RESULTS: There were an estimated 969 pregnancies with NTDs (168 (17%) births and 801(83%) terminations) in England and Wales in 2004. An estimated 44% of NTD terminations and 32% of births were not reported as such. The birth prevalence per 1000 decreased fallen 93% from 3.6 in 1964 to 0.3 in 2004, 59% due to an underlying decrease in the prevalence of NTDs and 34% due to screening diagnosis and subsequent termination of affected pregnancies. CONCLUSION: The prevalence of NTD pregnancies decreased by around two per 1000 from 1964 to 1990 and thereafter remained fairly constant. The prevalence of NTD pregnancies is substantially underestimated if it is based only on reported NTD births (by 88%) and also if it is based on reported NTD births and terminations (by 52%), because most NTD pregnancies in England and Wales are terminated following antenatal screening and most of these terminations are not reported.

Estimating the risk of Down's syndrome in antenatal screening and the gestation at which this risk applies.

Two equations are given to estimate the risk of a woman having a Down's syndrome pregnancy according to maternal age: one for use in estimating antenatal screening performance and the other for use in estimating an individual woman's risk of having an affected pregnancy. Because Down's syndrome pregnancies have an increased tendency to result in a spontaneous fetal loss, the estimation of a woman's risk of having an affected pregnancy will be dependent on gestational age. The best estimates of the prevalence of Down's syndrome are obtained from information relating to births and can reliably be adjusted to prevalence in early second trimester. The most reliable estimates of risk of a Down's syndrome pregnancy using all the currently used markers apply to early in the second trimester. These risks cannot accurately be adjusted to apply to term, because the first trimester markers have not in general been studied in pregnancies that continue to term. Therefore the early second trimester of pregnancy is the gestational age at which all screening performances should be given for the different antenatal screening programmes for Down's syndrome.

Validation plots in antenatal screening for Down's syndrome.

OBJECTIVE: To validate empirically the accuracy of antenatal Down's syndrome screening using the Integrated test, to compare this with other screening tests (including the Integrated test with the addition of cross trimester [CT] marker ratios) and to suggest how such validation analyses should be presented and interpreted. METHODS: Using data from 7809 unaffected and 27 Down's syndrome pregnancies that had had an Integrated test, risk estimates for various screening tests (maternal age, Double, Triple, Quadruple, Combined, Integrated and serum Integrated tests) that use Integrated test markers were categorized according to quintile categories of risk estimates of the 27 affected pregnancies. For each screening test, the median risk estimate for each category was plotted against the observed prevalence within each category. Such validation plots were also produced for the Integrated test with CT marker ratios by measuring the level of the serum markers in the trimester of pregnancy not already measured in stored samples of all affected and a one-in-five sample of unaffected pregnancies. The robustness of the method was assessed by repeating the analysis for the Integrated test after re-classifying affected pregnancies with low risk estimates as unaffected, simulating the underascertainment of cases. RESULTS: The validation plots (i) confirmed the accuracy of risk estimation for the different tests (by how close the points lay to the line of identity between predicted risk and observed prevalence), (ii) demonstrated the differences in screening performance of the different tests (by the range of risk spanned by the points and, in particular, the separation between the points representing the lowest risk and the next point), and (iii) are robust to underascertainment of affected pregnancies (by having little influence on the closeness of the points to the line of identity). CONCLUSION: The validation plot is a useful, simple and robust way to assess the validity of new screening methods, to assess the accuracy of risk estimation and to audit the performance of screening programmes.