Numbers of prenatal cell-free DNA screens performed: Results of a 2022 CAP exercise.

OBJECTIVE: Determine current analytical methods and number of cell-free (cf) DNA prenatal screening tests performed for common trisomies. METHODS: The College of American Pathologists 2022-B Noninvasive Prenatal Testing exercise was distributed in December 2022 to 93 participants in 22 countries. Supplemental questions included the number of tests performed in a recent month and the proportion of samples originating outside the United States (US). RESULTS: Eighty-three participants from three continents returned results; 74 (89%) were suitable for the analyses. Nine manufacturer/platform combinations were identified, most commonly Illumina/Nextseq (55%). The most common methodology was whole genome sequencing (76%). Annualized cfDNA tests were 2.80 million, with Asian, European and North American participants representing 10.6%, 6.5% and 82.9% of tests, respectively. When restricted to US in-country tests, the annualized rate was 2.18 million, with four of 20 participants testing 79.2%. Among 73 respondents, 63 (86%) were for-profit, eight (11%) were non-profit academic or government supported and the remaining two included hospital-based and private non-profit. Eighteen (25%) supported relevant academic training. CONCLUSION: In 2011, screening for common trisomies was based on serum/ultrasound markers with an estimated 2.96 million US pregnancies screened in 131 laboratories. In 2022, cfDNA-based screening was offered by 20 laboratories testing 2.18 million US pregnancies.

TSH and FT4 Reference Interval Recommendations and Prevalence of Gestational Thyroid Dysfunction: Quantification of Current Diagnostic Approaches.

CONTEXT: Guidelines recommend use of population- and trimester-specific thyroid-stimulating hormone (TSH) and free thyroxine (FT4) reference intervals (RIs) in pregnancy. Since these are often unavailable, clinicians frequently rely on alternative diagnostic strategies. We sought to quantify the diagnostic consequences of current recommendations. METHODS: We included cohorts participating in the Consortium on Thyroid and Pregnancy. Different approaches were used to define RIs: a TSH fixed upper limit of 4.0 mU/L (fixed limit approach), a fixed subtraction from the upper limit for TSH of 0.5 mU/L (subtraction approach) and using nonpregnancy RIs. Outcome measures were sensitivity and false discovery rate (FDR) of women for whom levothyroxine treatment was indicated and those for whom treatment would be considered according to international guidelines. RESULTS: The study population comprised 52 496 participants from 18 cohorts. Compared with the use of trimester-specific RIs, alternative approaches had a low sensitivity (0.63-0.82) and high FDR (0.11-0.35) to detect women with a treatment indication or consideration. Sensitivity and FDR to detect a treatment indication in the first trimester were similar between the fixed limit, subtraction, and nonpregnancy approach (0.77-0.11 vs 0.74-0.16 vs 0.60-0.11). The diagnostic performance to detect overt hypothyroidism, isolated hypothyroxinemia, and (sub)clinical hyperthyroidism mainly varied between FT4 RI approaches, while the diagnostic performance to detect subclinical hypothyroidism varied between the applied TSH RI approaches. CONCLUSION: Alternative approaches to define RIs for TSH and FT4 in pregnancy result in considerable overdiagnosis and underdiagnosis compared with population- and trimester-specific RIs. Additional strategies need to be explored to optimize identification of thyroid dysfunction during pregnancy.

Cell-free DNA-based prenatal screening via rolling circle amplification: Identifying and resolving analytic issues.

OBJECTIVE: A rolling circle amplification (RCA) based commercial methodology using cell-free (cf)DNA to screen for common trisomies became available in 2018. Relevant publications documented high detection but with a higher than expected 1% false positive rate. Preliminary evidence suggested assay variability was an issue. A multi-center collaboration was created to explore this further and examine whether subsequent manufacturer changes were effective. METHODS: Three academic (four devices) and two commercial (two devices) laboratories provided run date, chromosome 21, 18, and 13 run-specific standard deviations, number of samples run, and reagent lot identifications. Temporal trends and between-site/device consistency were explored. Proportions of run standard deviations exceeding pre-specified caps of 0.4%, 0.4% and 0.6% were computed. RESULTS: Overall, 661 RCA runs between April 2019 and July 30, 2022 tested 39,756 samples. In the first 24, subsequent 9, and final 7 months, proportions of capped chromosome 21 runs dropped from 39% to 22% to 6.0%; for chromosome 18, rates were 76%, 36%, and 4.0%. Few chromosome 13 runs were capped using the original 0.60%, but capping at 0.50%, rates were 28%, 16%, and 7.6%. Final rates occurred after reformulated reagents and imaging software modifications were fully implemented across all devices. Revised detection and false positive rates are estimated at 98.4% and 0.3%, respectively. After repeat testing, failure rates may be as low as 0.3%. CONCLUSION: Current RCA-based screening performance estimates are equivalent to those reported for other methods, but with a lower test failure rate after repeat testing.

Surveillance of SARS-CoV-2 Antibodies in Early 2020 among Rhode Island Pregnancies.

OBJECTIVE: Limited data are available on the performance of SARS-CoV-2 antibody assays and data collected during pregnancy vary widely. The objective of this study was to estimate the seroprevalence of antibodies against SARS-CoV-2 in pregnant individuals in Rhode Island and to evaluate whether the prevalence differed by month of collection, age, county of residence, or economic status as estimated by zip code. METHODS: Pre-pandemic (2019) and early pandemic (2020) serum samples, collected for prenatal screening between 15 and 22 weeks of gestation, were analyzed utilizing two SARS-CoV-2 immunoglobulin G (IgG) automated assays that targeted the viral nucleocapsid (anti-N) or spike (anti-S) receptor binding domain proteins. RESULTS: Among 756 pre-pandemic samples, one anti-S IgG and 13 anti-N IgG were identified. No samples were positive for both. Among 787 pandemic specimens, 16 (2.03%) were positive for both anti-N IgG and anti-S IgG. When stratified by month of collection, there was a significant increase in seropositivity rate (p=0.023). Seropositivity rates were associated with lower income levels (p=0.08) but this was not statistically significant. No trend by maternal age was found (p=0.70). CONCLUSIONS: When a positive result was defined as both anti-N IgG and anti-S IgG, false positives were unlikely. Based on this methodology, serology could be utilized to monitor infection trends during pregnancy.

Assessment of a Simplified Cell-Free DNA Method for Prenatal Down Syndrome Screening.

BACKGROUND: Prenatal screening for common trisomies via cell-free (cfDNA) is usually implemented by technologies utilizing massively parallel sequencing, stringent environmental controls, complex bioinformatics, and molecular expertise. An alternative and less complex methodology utilizes rolling circle amplification (RCA). Further evaluation of its performance and related requirements are warranted. METHODS: At 16 sites, women at 10 to 20 weeks gestation provided informed consent, relevant information, and 2 to 3 blood samples. Samples shipped for testing were processed and stored. Women were enrolled at primary cfDNA screening, or following such screening at referral for diagnostic testing. RCA testing occurred post-enrollment, over 11 months. Diagnostic results and delivery notes determined clinical truth. Detection rates were based on confirmed trisomic pregnancies; false-positive rates were based on unaffected pregnancies from the general population. RESULTS: Detection rate for the common trisomies was 95.9% (117/122, 95% CI, 90.5%-98.5%); overall false-positive rate was 1.00% (22/2,205, 0.65%-1.51%). Test failure rate after repeat testing was 0.04%. When assay standard deviations were below pre-specified levels, the overall false-positive rate was much lower at 0.30% (P < 0.001). Fetal sex calls were correct for 99.7%. One technician analyzed 560 samples over 2 weeks, a rate of 14 000/year. CONCLUSIONS: Our assessment of this simplified cfDNA-based system for prenatal screening for common trisomies performed in a prenatal screening laboratory is encouraging. Improved detection, low failure rates and rapid reporting can be achieved by collecting 2 samples. Future priorities should include achieving higher run precision using a single collection tube. CLINICALTRIALS.GOV REGISTRATION NUMBER: NCT03087357.

TSH and FT4 Reference Intervals in Pregnancy: A Systematic Review and Individual Participant Data Meta-Analysis.

CONTEXT: Interpretation of thyroid function tests during pregnancy is limited by the generalizability of reference intervals between cohorts due to inconsistent methodology. OBJECTIVE: (1) To provide an overview of published reference intervals for thyrotropin (TSH) and free thyroxine (FT4) in pregnancy, (2) to assess the consequences of common methodological between-study differences by combining raw data from different cohorts. METHODS: (1) Ovid MEDLINE, EMBASE, and Web of Science were searched until December 12, 2021. Studies were assessed in duplicate. (2) The individual participant data (IPD) meta-analysis was performed in participating cohorts in the Consortium on Thyroid and Pregnancy. RESULTS: (1) Large between-study methodological differences were identified, 11 of 102 included studies were in accordance with current guidelines; (2) 22 cohorts involving 63 198 participants were included in the meta-analysis. Not excluding thyroid peroxidase antibody-positive participants led to a rise in the upper limits of TSH in all cohorts, especially in the first (mean +17.4%; range +1.6 to +30.3%) and second trimester (mean +9.8%; range +0.6 to +32.3%). The use of the 95th percentile led to considerable changes in upper limits, varying from -10.8% to -21.8% for TSH and -1.2% to -13.2% for FT4. All other additional exclusion criteria changed reference interval cut-offs by a maximum of 3.5%. Applying these findings to the 102 studies included in the systematic review, 48 studies could be used in a clinical setting. CONCLUSION: We provide an overview of clinically relevant reference intervals for TSH and FT4 in pregnancy. The results of the meta-analysis indicate that future studies can adopt a simplified study setup without additional exclusion criteria.

An Educational Assessment of Evidence Used for Variant Classification: A Report of the Association for Molecular Pathology.

The Association for Molecular Pathology Variant Interpretation Testing Among Laboratories (VITAL) Working Group convened to evaluate the Standards and Guidelines for the Interpretation of Sequence Variants implementation into clinical practice, identify problematic classification rules, and define implementation challenges. Variants and associated clinical information were provided to volunteer respondents. Participant variant classifications were compared with intended consensus-derived classifications of the Working Group. The 24 variant challenges received 1379 responses; 1119 agreed with the intended response (81%; 95% CI, 79% to 83%). Agreement ranged from 44% to 100%, with 16 challenges (67%; 47% to 82%) reaching consensus (≥80% agreement). Participant classifications were also compared to a calculated interpretation of the ACMG Guidelines using the participant-reported criteria as input. The 24 variant challenges had 1368 responses with specific evidence provided and 1121 (82%; 80% to 84%) agreed with the calculated interpretation. Agreement for challenges ranged from 63% to 98%; 15 (63%; 43% to 79%) reaching consensus. Among 81 individual participants, 32 (40%; 30% to 50%) reached agreement with at least 80% of the intended classifications and 42 (52%; 41% to 62%) with the calculated classifications. This study demonstrated that although variant classification remains challenging, published guidelines are being utilized and adapted to improve variant calling consensus. This study identified situations where clarifications are warranted and provides a model for competency assessment.

Preeclampsia at delivery is associated with lower serum vitamin D and higher antiangiogenic factors: a case control study.

BACKGROUND: Preeclampsia is characterized by decreased trophoblastic angiogenesis leading to abnormal invasion of spiral arteries, shallow implantation and resulting in compromised placentation with poor uteroplacental perfusion. Vitamin D plays an important role in pregnancy influencing implantation, angiogenesis and placental development. The objective of this study was to determine whether there is an association between serum vitamin D levels, and anti-angiogenic factors at the time of delivery and the occurrence of preeclampsia. METHODS: This nested case control study analyzed frozen serum samples at the time of delivery and related clinical data from women with singleton liveborn pregnancies who had participated in studies of the NICHD Stillbirth Collaborative Research Network. Women with a recorded finding of preeclampsia and who had received magnesium sulfate treatment prior to delivery were considered index cases (N = 56). Women without a finding of preeclampsia were controls (N = 341). RESULTS: Women with preeclampsia had 14.5% lower serum vitamin D levels than women in the control group (16.5 ng/ml vs. 19 ng/ml, p = 0.014) with 64.5% higher sFlt-1 levels (11,600 pg/ml vs. 7050 pg/ml, p < 0.001) and greater than 2 times higher endoglin levels (18.6 ng/ml vs. 8.7 ng/ml, < 0.001). After controlling for gestational age at delivery and maternal BMI, vitamin D levels were 0.88 times lower (P = 0.051), while endoglin levels were 2.5 times higher and sFlt-1 levels were 2.1 times higher than in control pregnancies (P < 0.001). CONCLUSIONS: Women with preeclampsia at time of delivery have higher maternal antiangiogenetic factors and may have lower maternal serum vitamin D levels. These findings may lead to a better understanding of the underlying etiology of preeclampsia as well as possible modifiable treatment options which could include assuring adequate levels of maternal serum vitamin D prior to pregnancy.

Prenatal serum screening for Down syndrome and neural tube defects in the United States: Changes in utilization patterns from 2012 to 2020.

OBJECTIVE: To compile current usage of serum-based prenatal screening for Down syndrome in the United States and compare it with results from a similar 2011/2012 survey. SETTING: The College of American Pathologists maternal screening proficiency testing survey includes a supplemental question on the first of three yearly distributions. METHODS: Information regarding tests offered and the monthly number of pregnancies tested for US-based laboratories were reviewed. Results were stratified by size of laboratory, tests offered, and pregnancies tested. Findings were compared to an earlier survey. RESULTS: Fifty-six laboratories reported they will have screened 1,131,336 pregnancies in 2020. Of these, 36% are screened by stand-alone first trimester testing, 48% by stand-alone second trimester testing, and 16% using tests that integrate results from both trimesters. Eighty percent of all serum screens were provided by the five laboratories that performed the most screens (at least 50,000). These five performed similar proportions of first or second trimester screens (42.2% and 41.8%, respectively). Compared to eight years earlier, there are now 54% fewer laboratories. Pregnancies screened using the first trimester, second trimester, and integrated protocols were lower by 27%, 69%, and 72%, respectively. The serum screening activity in the US showed a 62% decrease from 2012 levels. During 2012-2020, the number of cell-free DNA tests increased from negligible to 1,492,332. CONCLUSIONS: Maternal serum screening for common aneuploidies has changed significantly in eight years with fewer laboratories, a shift toward larger laboratories and a 2.5-fold reduction in pregnancies tested, likely due to the introduction of cell-free DNA screening.

Increased chemotherapy-induced ovarian reserve loss in women with germline BRCA mutations due to oocyte deoxyribonucleic acid double strand break repair deficiency.

OBJECTIVE: To assess whether woman who have BRCA mutations (WBM) experience more declines in ovarian reserve after chemotherapy treatment, as it induces oocyte death by deoxyribonucleic acid (DNA) damage, and BRCA mutations result in DNA damage repair deficiency. DESIGN: Longitudinal cohort study. SETTING: Academic centers. PATIENT(S): The 108 evaluable women with breast cancer were stratified into those never tested (negative family history; n = 35) and those negative (n = 59) or positive (n = 14) for a pathogenic BRCA mutation. INTERVENTION(S): Sera were longitudinally obtained before and 12-24 months after chemotherapy treatment, assayed for antimüllerian hormone (AMH), and adjusted for age at sample collection. MAIN OUTCOME MEASURE(S): Ovarian recovery, defined as the geometric mean of the after chemotherapy age-adjusted AMH levels compared with baseline levels. RESULT(S): Compared with the controls, the before chemotherapy treatment AMH levels were 24% and 34% lower in those negative or positive for BRCA mutations, consistent with accelerated ovarian aging in WBM. The WBM had a threefold difference in AMH recovery after chemotherapy treatment (1.6%), when compared with BRCA negative (3.7%) and untested/low risk controls (5.2%). Limiting the analysis to the most common regimen, doxorubicin and cyclophosphamide followed by paclitaxel, showed similar results. These findings were mechanistically confirmed in an in vitro mouse oocyte BRCA knockdown bioassay, which showed that BRCA deficiency results in increased oocyte susceptibility to doxorubicin. CONCLUSION(S): Women who have pathogenic BRCA mutations are more likely to lose ovarian reserve after chemotherapy treatment, suggesting an emphasis on fertility preservation. Furthermore, our findings generate the hypothesis that DNA repair deficiency is a shared mechanism between aging, infertility, and cancer. CLINICAL TRIAL REGISTRATION NUMBER: NCT00823654.

Adjusting antimüllerian hormone levels for age and body mass index improves detection of polycystic ovary syndrome.

OBJECTIVE: To examine whether accounting for a woman's age and body mass index (BMI) would improve the ability of antimüllerian hormone (AMH) to distinguish between women with (cases) and without (controls) polycystic ovarian syndrome (PCOS). DESIGN: An opportunistic case-control dataset of reproductive age women having evaluations for PCOS as defined by National Institutes of Health criteria. SETTING: Two medical centers in the United States enrolled women. Serum samples were analyzed for relevant analytes. PATIENTS: Women were between 18 and 39 years of age when samples and clinical information were collected. Residual samples had been stored for 2-17 years. AMH was measured via immunoassay. INTERVENTIONS: None; this was an observational study. MAIN OUTCOME MEASURES: Detection and false-positive rates for PCOS were computed for AMH results expressed as multiples of the median (MoM) both before and after adjustment for the woman's age and BMI. RESULTS: Using unadjusted AMH MoM results, 168 cases (78%) cases were at or beyond the 90th centile of controls (2.47 MoM). After accounting for each woman's age and BMI, 188 (87%) of those women were beyond the 90th centile of controls (2.20 MoM), a significant increase (P = .015). The adjusted AMH MoM levels fitted logarithmic normal distributions well (mean, standard deviation for controls and cases of 0.0000, 0.2765 and 0.6884, 0.2874, respectively) and this allowed for computation of patient-specific PCOS risks. CONCLUSIONS: Accounting for the woman's age and BMI resulted in significantly higher AMH-based detection rates for PCOS at a 10% false-positive rate, and patient-specific PCOS risks could be computed.

Assessment of laboratories offering cell-free (cf) DNA screening for Down syndrome: results of the 2018 College of American Pathology External Educational Exercises.

PURPOSE: Summarize and interpret results from exercises distributed to laboratories offering cell-free (cf) DNA screening for Down syndrome. METHODS: The College of American Pathologists distributed three patient-derived plasma specimens twice in 2018. Sequencing platforms, test methods, results, and responses to supplemental questions were collected. Results were not graded but discrepancies were identified. RESULTS: Sixty-five laboratories from six continents enrolled; six provided no results. The most common methodology was shotgun/genome sequencing (39/56, 70%). Overall, 40% of the gestational or maternal age responses were incorrect but 45% of the errors were corrected by the next distribution. Fetal fractions from 54 responding laboratories generally agreed with the intended response. No genotyping errors occurred (40/40 for trisomy 21 and 226/226 for euploid challenges) but 10 additional tests failed (3.6%). All 213 fetal sex calls were correct. Participants reported their clinical text for a Down syndrome screen positive test; 39% were classified as inadequate or misleading. CONCLUSION: Patient-derived materials are suitable for all enrolled technologies/methodologies, but collecting material is challenging. Suggested clinical text includes the terms "screen positive" and "screen negative." Overall, laboratories performed well. Future efforts will focus on potential manufactured samples, clarifying results reporting and including additional chromosome abnormalities.

Laboratory screening and diagnosis of open neural tube defects, 2019 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG).

Open neural tube defects (ONTDs) include open spina bifida (OSB) and anencephaly. These defects are caused by incomplete closure of the neural tube at about 4 weeks of pregnancy. Levels of early second-trimester maternal serum (ms) alpha-fetoprotein (AFP) are sufficiently elevated in affected pregnancies to be used as a population-based screening test. The basic screening methodology was described in the late 1970s and screening programs were active a few years later. By identifying pregnancies with the highest msAFP levels, about 80% of OSB and 95% of anencephaly can be identified as early as 16 weeks gestation. The interpretation of msAFP levels is complicated by the need to consider multiple factors such as gestational age, maternal weight, maternal race, multiple gestations, and more. Testing for AFP and acetylcholinesterase in amniotic fluid and/or identification of the lesion by targeted ultrasound is considered diagnostic of ONTD. When a diagnosis is made, options include termination, surgery after delivery, or in utero surgery, depending on factors such as location and size of the defect, and the presence of any additional anomalies. Screening for ONTD should be performed as part of a comprehensive program linking primary obstetrical care providers, laboratorians, and high-risk clinicians.

Levels of angiogenic markers in second-trimester maternal serum from in vitro fertilization pregnancies with oocyte donation.

OBJECTIVE: To determine whether differences exist in angiogenic placental growth factor (PlGF) and antiangiogenic soluble vascular endothelial growth factor receptor 1 (sVEGFR-1; both being early markers of placental ischemic disease) in oocyte-donation (OD) pregnancies, compared with autologous in vitro fertilization (aIVF) and spontaneous pregnancies. DESIGN: Case-control study of residual second-trimester serum samples from women undergoing prenatal screening. SETTING: Academic medical center. PATIENT(S): Fifty-seven OD pregnancies were identified. Each OD pregnancy was matched to two spontaneous pregnancies (n = 114) and one aIVF pregnancy (n = 57). INTERVENTIONS(S): None. MAIN OUTCOME MEASURE(S): Second-trimester serum PlGF and sVEGFR-1 levels. RESULT(S): sVEGFR-1, PlGF, and unconjugated E2 levels were similar among the three study groups. The ratio of sVEGFR-1 to PlGF was significantly higher in the OD group. Consistently with previous studies, alpha-fetoprotein (AFP) in the OD group was significantly elevated compared with spontaneous pregnancy. Both aIVF and OD groups had greater levels of inhibin A than the spontaneous pregnancy group, and the OD group had significantly higher levels of inhibin A than the aIVF group. hCG levels were significantly elevated in aIVF compared with spontaneous pregnancy; however, levels were not different between aIVF and OD. CONCLUSION(S): Second-trimester serum sVEGFR-1 and PlGF levels were not significantly altered in OD pregnancies. Our data support previous findings that OD pregnancies have uniquely increased second-trimester AFP, hCG, and inhibin A levels compared with aIVF. However, the biologic basis of these marker elevations in OD may not be related to placental angiogenesis.

Maternal BMI, Peripheral Deiodinase Activity, and Plasma Glucose: Relationships Between White Women in the HAPO Study.

OBJECTIVES: Explore the maternal body mass index (BMI) relationship with peripheral deiodinase activity further. Examine associations between deiodinase activity, glucose, and C-peptide. Consider findings in the historical context of related existing literature. DESIGN: Identify fasting plasma samples and selected demographic, biophysical, and biochemical data from a subset of 600 randomly selected non-Hispanic white women recruited in the Hyperglycemia Adverse Pregnancy Outcomes (HAPO) study, all with glucose tolerance testing [545 samples sufficient to measure TSH, free T4 (fT4), and T3]. Exclude highest and lowest 1% TSH values (535 available for analysis). Assess deiodinase activity by using T3/fT4 ratios. Among women with and without gestational diabetes mellitus (GDM), compare thyroid measurements, C-peptide, and other selected data. Examine relationships independent of GDM status between BMI and thyroid hormones and between thyroid hormones and glucose and C-peptide. RESULTS: Levels of BMI, T3/fT4 ratio, and T3 were significantly higher among women with GDM (P = 0.01, 0.005, and 0.001, respectively). Irrespective of GDM status, maternal BMI was associated directly with both T3/fT4 ratio (r = 0.40, P < 0.001) and T3 (r = 0.34, P < 0.001) but inversely with fT4 (r = -0.21, P < 0.001). In turn, fasting thyroid hormone levels (most notably T3/fT4 ratio) were directly associated with maternal glucose [z score sum (fasting, 1, 2 hours); r = 0.24, P < 0.001] and with C-peptide [z score sum (fasting, 1 hour); r = 0.27, P < 0.001]. CONCLUSIONS: Higher BMI was associated with increased deiodinase activity, consistent with reports from elsewhere. Increased deiodinase activity, in turn, was associated with higher glucose. Deiodinase activity accounts for a small percentage of z score sum glucose.

Fewer women aged 35 and older choose serum screening for Down's syndrome: Impact and implications.

OBJECTIVE: To quantify changes in the proportion of women aged 35 and older choosing serum screening for Down's syndrome over time and the effect on false positive and detection rates. METHODS: From Rhode Island hospital-based laboratory prenatal screening records (2013-2017) we extracted the test performed (Integrated, Combined, Quadruple), maternal age, and Down's syndrome risk; documented observed changes in maternal age distributions and false positive rates, and modelled the impact of varying proportions of older women choosing screening on each test's performance using the 2015 United States birth cohort as baseline. RESULTS: Over five years, observed false positive rates for Integrated testing declined from 1.9 to 1.3% (-32%). The proportion of older women tested declined from 14.9 to 8.5%, from which modelling predicts a 16% decline in the false positive rate. This is lower than our observed change but consistent with a reduction driven by declining participation by older women. Modelling predicted a detection rate reduction from 89 to 87%. Larger detection rate impacts were predicted for Combined and Quadruple testing. CONCLUSIONS: This study documents, for the first time, the declining proportion of older women choosing Down's syndrome serum screening and subsequent impact on screening performance. The American College of Obstetrics and Gynecology recommends offering cell-free DNA screening for these 'high risk' pregnancies and uptake may increase further. Screening programmes could consider increasing use of Integrated testing over other serum screening tests or lowering risk cut-offs so false positive rates approach those of 2012 to regain lost detection.