Free beta-hCG as first-trimester marker for fetal trisomy

Effect of maternal polycystic ovary syndrome (PCOS) on screening of aneuploidy in the first and second trimesters

BACKGROUND

Polycystic ovary syndrome (PCOS) is characterized by insulin resistance and hormonal disorder in women. This study aimed to assess the effect of maternal PCOS on screening of aneuploidy in the first and second-trimesters.

METHODS

This case-control study was conducted in Arash Hospital and Nilou Laboratory in 2017-2018. The screening test was conducted on 90 PCOS and 90 healthy mothers. Finally, the first and second-trimester screening was compared between the two groups using Chi-square, Mann-Whitney's U and students T tests and regression model by SPSS 21. P < 0.05 was considered as statistically significant.

RESULTS

Free Beta-Human Chorionic Gonadotropin (Free-β-HCG) (P = 0.04), inhibin-A (P = 0.001) and Alpha Fetoprotein (AFP) (P = 0.02) levels were higher in the PCOS women comparing to the healthy women but there was no significant difference between the mean of HCG, Plasma Protein A (PAPP-A), and Unconjugated Estriol (UE3) between the two groups. Pre-eclampsia (P < 0.001) and trisomy 18 risks in quad screening were higher in the PCOS women (P = 0.002) than the control group; however, trisomy 13, trisomy 18 and trisomy 21 risks, Smith-Lemli-Opitz Syndrome (SLOS) and Neural Tube Defect (NTD) risks were not different between the two groups. The logistic regression model showed that the first- and second-trimester screening of aneuploidywas related to PCOS.

CONCLUSIONS

There was a significant difference in the mean of free-β-HCG, inhibin-A, AFP level, and the risks of pre-eclampsia, SLOS and trisomy 18 between the two groups but no significant association was found in the mean of HCG, PAPP-A, UE3, NTD and other aneuploidies between the two groups. PCOS may affect the first- and second-trimester screening tests and pregnancy health. It may also require correction in the calculation of risks related to the first- and second-trimester screening for aneuploidy.

Maternal steroid levels and the autistic traits of the mother and infant

BACKGROUND

Prenatal sex steroids have been associated with autism in several clinical and epidemiological studies. It is unclear how this relates to the autistic traits of the mother and how early this can be detected during pregnancy and postnatal development.

METHODS

Maternal serum was collected from pregnant women (n = 122) before or during their first ultrasound appointment [mean = 12.7 (SD = 0.7) weeks]. Concentrations of the following were measured via immunoassays: testosterone, estradiol, dehydroepiandrosterone sulphate, progesterone; and sex hormone-binding globulin which was used to compute the free fractions of estradiol (FEI) and testosterone (FTI). Standardised human choriogonadotropin (hCG) and pregnancy-associated plasma protein A (PAPP-A) values were obtained from clinical records corresponding to the same serum samples. Mothers completed the Autism Spectrum Quotient (AQ) and for their infants, the Quantitative Checklist for Autism in Toddlers (Q-CHAT) when the infants were between 18 and 20 months old.

RESULTS

FEI was positively associated with maternal autistic traits in univariate (n = 108, Pearson's r = 0.22, p = 0.019) and multiple regression models (semipartial r = 0.19, p = 0.048) controlling for maternal age and a diagnosis of PCOS. Maternal estradiol levels significantly interacted with fetal sex in predicting infant Q-CHAT scores, with a positive relationship in males but not females (n = 100, interaction term: semipartial r = 0.23, p = 0.036) after controlling for maternal AQ and other covariates. The opposite was found for standardised hCG values and Q-CHAT scores, with a positive association in females but not in males (n = 151, interaction term: r = -0.25, p = 0.005).

LIMITATIONS

Sample size of this cohort was small, with potential ascertainment bias given elective recruitment. Clinical covariates were controlled in multiple regression models, but additional research is needed to confirm the statistically significant findings in larger cohorts.

CONCLUSION

Maternal steroid factors during pregnancy are associated with autistic traits in mothers and their infants.

Unbalanced human embryos secrete more hyperglycosylated human chorionic gonadotrophin (hCG-H) than balanced ones

PURPOSE

The aim of this study was to compare the levels of hyperglycosylated human chorionic gonadotropin (hCG-H) secreted from balanced and unbalanced human embryos.

METHODS

Single-step culture media samples from 155 good quality embryos, derived from 90 good prognosis patients undergoing intracytoplasmic sperm injection (ICSI), were collected on the fifth day of embryo cultivation. All embryos were tested by next-generation sequencing (NGS) technique. The hCG-H levels in the culture media were evaluated by ELISA kit (Cusabio Biotech, CBS-E15803h) according to the manufacturer's instructions. Statistical analysis was performed using SPSS v.21 (IBM Corp., Armonk, NY, USA).

RESULTS

The NGS analysis revealed that 36% of the embryos (n = 56) were balanced, and 64% of the embryos were unbalanced (n = 99). The presence of hCG-H was confirmed in all embryo culture media samples but was absent in the negative control. In addition, hCG-H concentration was significantly higher in the culture media from unbalanced embryos compared with the balanced ones (0.72 ± 0.30 mIU/ml vs. 0.62 ± 0.12 mIU/ml, p = 0.02, respectively). Furthermore, the mean levels of hCG-H were significantly increased in the samples from embryos with multiple abnormalities. Finally, the highest levels of hCG-H were expressed from embryos with monosomy of chromosome 11 (1.28 ± 0.04 mIU/ml) and those with trisomies of chromosomes 21 (2.23 mIU/ml) and 4 (1.02 ± 0.35 mIU/ml).

CONCLUSION

Our results suggest that chromosomal aberrations in human embryos are associated with an increased secretion of hCG-H. However, hCG-H concentration in embryo culture media as a single biomarker is not sufficient for an accurate selection of balanced embryos.

The prediction of early preeclampsia: Results from a longitudinal proteomics study

OBJECTIVES

To identify maternal plasma protein markers for early preeclampsia (delivery <34 weeks of gestation) and to determine whether the prediction performance is affected by disease severity and presence of placental lesions consistent with maternal vascular malperfusion (MVM) among cases.

STUDY DESIGN

This longitudinal case-control study included 90 patients with a normal pregnancy and 33 patients with early preeclampsia. Two to six maternal plasma samples were collected throughout gestation from each woman. The abundance of 1,125 proteins was measured using high-affinity aptamer-based proteomic assays, and data were modeled using linear mixed-effects models. After data transformation into multiples of the mean values for gestational age, parsimonious linear discriminant analysis risk models were fit for each gestational-age interval (8-16, 16.1-22, 22.1-28, 28.1-32 weeks). Proteomic profiles of early preeclampsia cases were also compared to those of a combined set of controls and late preeclampsia cases (n = 76) reported previously. Prediction performance was estimated via bootstrap.

RESULTS

We found that 1) multi-protein models at 16.1-22 weeks of gestation predicted early preeclampsia with a sensitivity of 71% at a false-positive rate (FPR) of 10%. High abundance of matrix metalloproteinase-7 and glycoprotein IIbIIIa complex were the most reliable predictors at this gestational age; 2) at 22.1-28 weeks of gestation, lower abundance of placental growth factor (PlGF) and vascular endothelial growth factor A, isoform 121 (VEGF-121), as well as elevated sialic acid binding immunoglobulin-like lectin 6 (siglec-6) and activin-A, were the best predictors of the subsequent development of early preeclampsia (81% sensitivity, FPR = 10%); 3) at 28.1-32 weeks of gestation, the sensitivity of multi-protein models was 85% (FPR = 10%) with the best predictors being activated leukocyte cell adhesion molecule, siglec-6, and VEGF-121; 4) the increase in siglec-6, activin-A, and VEGF-121 at 22.1-28 weeks of gestation differentiated women who subsequently developed early preeclampsia from those who had a normal pregnancy or developed late preeclampsia (sensitivity 77%, FPR = 10%); 5) the sensitivity of risk models was higher for early preeclampsia with placental MVM lesions than for the entire early preeclampsia group (90% versus 71% at 16.1-22 weeks; 87% versus 81% at 22.1-28 weeks; and 90% versus 85% at 28.1-32 weeks, all FPR = 10%); and 6) the sensitivity of prediction models was higher for severe early preeclampsia than for the entire early preeclampsia group (84% versus 71% at 16.1-22 weeks).

CONCLUSION

We have presented herein a catalogue of proteome changes in maternal plasma proteome that precede the diagnosis of preeclampsia and can distinguish among early and late phenotypes. The sensitivity of maternal plasma protein models for early preeclampsia is higher in women with underlying vascular placental disease and in those with a severe phenotype.

Maternal circulating miRNAs that predict infant FASD outcomes influence placental maturation

Maternal gestational circulating microRNAs, predictive of adverse infant outcomes, including growth deficits, following prenatal alcohol exposure, contribute to placental pathology by impairing the EMT pathway in trophoblasts.

Prenatal alcohol exposure (PAE), like other pregnancy complications, can result in placental insufficiency and fetal growth restriction, although the linking causal mechanisms are unclear. We previously identified 11 gestationally elevated maternal circulating miRNAs (_HEamiRNAs) that predicted infant growth deficits following PAE. Here, we investigated whether these _HEamiRNAs contribute to the pathology of PAE, by inhibiting trophoblast epithelial–mesenchymal transition (EMT), a pathway critical for placental development. We now report for the first time that PAE inhibits expression of placental pro-EMT pathway members in both rodents and primates, and that _HEamiRNAs collectively, but not individually, mediate placental EMT inhibition. _HEamiRNAs collectively, but not individually, also inhibited cell proliferation and the EMT pathway in cultured trophoblasts, while inducing cell stress, and following trophoblast syncytialization, aberrant endocrine maturation. Moreover, a single intravascular administration of the pooled murine-expressed _HEamiRNAs, to pregnant mice, decreased placental and fetal growth and inhibited the expression of pro-EMT transcripts in the placenta. Our data suggest that _HEamiRNAs collectively interfere with placental development, contributing to the pathology of PAE, and perhaps also, to other causes of fetal growth restriction.

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.

Screening for fetal growth restriction using fetal biometry combined with maternal biomarkers

Fetal growth restriction is a major determinant of perinatal morbidity and mortality. Screening for fetal growth restriction is a key element of prenatal care but it is recognized to be problematic. Screening using clinical risk assessment and targeting ultrasound to high-risk women is the standard of care in the United States and United Kingdom, but the approach is known to have low sensitivity. Systematic reviews of randomized controlled trials do not demonstrate any benefit from universal ultrasound screening for fetal growth restriction in the third trimester, but the evidence base is not strong. Implementation of universal ultrasound screening in low-risk women in France failed to reduce the risk of complications among small-for-gestational-age infants but did appear to cause iatrogenic harm to false positives. One strategy to making progress is to improve screening by developing more sensitive and specific tests with the key goal of differentiating between healthy small fetuses and those that are small through fetal growth restriction. As abnormal placentation is thought to be the major cause of fetal growth restriction, one approach is to combine fetal biometry with an indicator of placental dysfunction. In the past, these indicators were generally ultrasonic measurements, such as Doppler flow velocimetry of the uteroplacental circulation. However, another promising approach is to combine ultrasonic suspicion of small-for-gestational-age infant with a blood test indicating placental dysfunction. Thus far, much of the research on maternal serum biomarkers for fetal growth restriction has involved the secondary analysis of tests performed for other indications, such as fetal aneuploidies. An exemplar of this is pregnancy-associated plasma protein A. This blood test is performed primarily to assess the risk of Down syndrome, but women with low first-trimester levels are now serially scanned in later pregnancy due to associations with placental causes of stillbirth, including fetal growth restriction. The development of "omic" technologies presents a huge opportunity to identify novel biomarkers for fetal growth restriction. The hope is that when such markers are measured alongside ultrasonic fetal biometry, the combination would have strong predictive power for fetal growth restriction and its related complications. However, a series of important methodological considerations in assessing the diagnostic effectiveness of new tests will have to be addressed. The challenge thereafter will be to identify novel disease-modifying interventions, which are the essential partner to an effective screening test to achieve clinically effective population-based screening.

The maternal plasma proteome changes as a function of gestational age in normal pregnancy: a longitudinal study

OBJECTIVE

Pregnancy is accompanied by dramatic physiological changes in maternal plasma proteins. Characterization of the maternal plasma proteome in normal pregnancy is an essential step for understanding changes to predict pregnancy outcome. The objective of this study was to describe maternal plasma proteins that change in abundance with advancing gestational age and determine biological processes that are perturbed in normal pregnancy.

STUDY DESIGN

A longitudinal study included 43 normal pregnancies that had a term delivery of an infant who was appropriate for gestational age without maternal or neonatal complications. For each pregnancy, 3 to 6 maternal plasma samples (median, 5) were profiled to measure the abundance of 1125 proteins using multiplex assays. Linear mixed-effects models with polynomial splines were used to model protein abundance as a function of gestational age, and the significance of the association was inferred via likelihood ratio tests. Proteins considered to be significantly changed were defined as having the following: (1) >1.5-fold change between 8 and 40 weeks of gestation; and (2) a false discovery rate-adjusted value of P < .1. Gene ontology enrichment analysis was used to identify biological processes overrepresented among the proteins that changed with advancing gestation.

RESULTS

The following results were found: (1) Ten percent (112 of 1125) of the profiled proteins changed in abundance as a function of gestational age; (2) of the 1125 proteins analyzed, glypican-3, sialic acid-binding immunoglobulin-type lectin-6, placental growth factor, C-C motif-28, carbonic anhydrase 6, prolactin, interleukin-1 receptor 4, dual-specificity mitogen-activated protein kinase 4, and pregnancy-associated plasma protein-A had more than a 5-fold change in abundance across gestation (these 9 proteins are known to be involved in a wide range of both physiological and pathological processes, such as growth regulation, embryogenesis, angiogenesis immunoregulation, inflammation etc); and (3) biological processes associated with protein changes in normal pregnancy included defense response, defense response to bacteria, proteolysis, and leukocyte migration (false discovery rate, 10%).

CONCLUSION

The plasma proteome of normal pregnancy demonstrates dramatic changes in both the magnitude of changes and the fraction of the proteins involved. Such information is important to understand the physiology of pregnancy and the development of biomarkers to differentiate normal vs abnormal pregnancy and determine the response to interventions.

Effect of ethnicity on first trimester biomarkers for combined trisomy 21 screening: results from a multicenter study in six Asian countries

OBJECTIVE

To assess differences between first trimester trisomy 21 screening markers free beta chain of the human chorionic gonadotrophin (βhCG) and pregnancy-associated plasma protein A (PAPP-A) in pregnant women of six different Asian countries (China, Indonesia, Korea, Taiwan, Thailand, and Vietnam) and compare serum levels with those in women of European countries.

METHODS

Median and multiple of median (MoM) values of free βhCG and PAPP-A were determined in more than 3000 pregnant women from the Asian countries during their first trimester of pregnancy. Differences in MoM values between a European reference group from a previous multicenter evaluation and the Asian population were evaluated. Two different types of population correction factors for T21 risk estimation were assessed.

RESULTS

An at least 10% difference of median MoMs between European and Asian PAPP-A values was found to be statistically significant (p < 0.0001). The specificity of the screening did not show a big difference in individual countries, when using the country-specific correction factor compared with the overall Asian correction factor (<1.4%).

CONCLUSIONS

The use of a correction factor is recommended based on the differences in European and Asian MoM values. Developing country-specific medians in larger study populations can help identify clinical relevant differences and give the opportunity to explore a more accurate risk calculation.

A historical and practical review of first trimester aneuploidy screening

There have been tremendous advancements over the past three decades in prenatal screening for aneuploidy and we have changed our practice from screening by maternal age alone to 'combined' first trimester screening and circulating cell-free fetal DNA. We currently use the nuchal translucency and biochemical markers of free β-hCG and PAPP-A to determine the risk of fetal aneuploidy. The primary goal is to identify higher risk women for fetal aneuploidy early in pregnancy and give them the option to pursue invasive testing in a timely manner if desired.

Screening for Down Syndrome in the United States: Results of Surveys in 2011 and 2012

Context.—Participants in a College of American Pathologists external proficiency testing program for first and second trimester Down syndrome screening.

Objectives.—To determine the number of women screened for Down syndrome in the United States, along with the type of test received and to compare those results to earlier surveys in 1988 and 1992.

Design.—Questionnaires regarding the type and number of Down syndrome tests performed per month were completed by participants in early 2011 and again in early 2012.

Results.—After accounting for some of the missing responses, data from up to 131 laboratories indicated that 67% (2 764 020 of 4 130 000) to 72% (2012: 2 963 592 of 4 130 000) of US pregnancies received prenatal screening for Down syndrome. Second trimester tests were most common (2012: 60%; 1 770 024 of 2 963 592), followed by integrated (2012: 21%; 627 876 of 2 963 592), and first trimester (2012: 19%; 565 692 of 2 963 592). The 6 largest laboratories tested 61% of screened pregnancies and offered the widest array of tests, while the smallest 32 tested 1% and almost always offered only second trimester tests.

Conclusions.—The current population estimate of 72% pregnancies screened annually is higher than estimates from 1988 (25%) and 1992 (50%). Available testing choices are also more varied, and all testing methods perform better than those methods available 10 years ago. Clinicians should ensure that women are offered tests that follow recommended best-practice testing protocols, and screening laboratories should assess whether patient needs are being met.

The assessment of nuchal translucency and serum markers for down syndrome screening with ductus venosus Doppler measurements in the first trimester

OBJECTIVE

The aim of the study was to improve nuchal translucency (NT) and serum marker Down syndrome (Tri21) screening methods by including fetal ductus venosus (DV) Doppler measurements.

MATERIAL AND METHODS

A total of 213 pregnant women were screened consecutively by combining maternal age, fetal NT and maternal serum pregnancy associated plasma protein A (PAPP-A) and free β-human chorionic gonadotropin (f β-HCG) values at 11-14 weeks of gestation. Also, a DV Doppler analysis was performed for the contribution to the screening for Tri21 and other fetal anomalies or adverse pregnancy outcomes.

RESULTS

Twelve fetuses had DV PI measurements above the 95th percentile and two (17%) developed intrauterine growth retardation. DV PI values negatively correlated with birth weight (p=0.013, r=0.171). Two patients had T 21 among the study group (0.9%) with abnormal biochemical screening results. In these with Tri21, the combined test risk was above the suggested limit (>1/250). PAPP-A was <0.4 MoM in 23, and f β-HCG was >1.91 MoM in 49 patients. The rates of false positivity were 10% for PAPP-A and 22% for f β-HCG. The sensitivity, specificity, positive and negative predictive values of the combined test was 100%, 95%, 20% and 100%, respectively.

CONCLUSION

The combined test has high sensitivity and specificity for Tri21 detection. The addition of DV Doppler ultrasound in the first trimester might have the advantage of predicting some adverse pregnancy outcomes. However, in the Turkish population, further studies with larger numbers of patients will be needed to establish the usefulness of DV for the detection of Tri21 or the prediction of some major cardiac anomalies.

[First trimester screening for Down syndrome: five years prospective experience]

First trimester screening for Down syndrome is yet to become the first intention strategy in France. This screening program at 11-14 weeks of gestation using maternal age, fetal nuchal translucency, maternal serum free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A has already been validated for a long time by many international studies. It seems to improve detection rate and decrease false positive rates. We report here five years prospective experience.

ADAM12 as a marker of trisomy 18 in the first and second trimester of pregnancy

BACKGROUND

ADAM12 (a disintegrin and metalloprotease 12) is a placentally derived glycoprotein that appears to be involved in growth and differentiation. The maternal serum concentration of ADAM12 appears to be a very good marker of trisomy 21 in the early first trimester when levels are reduced, and in the second trimester around 16-18 weeks levels are elevated. One small preliminary study of first trimester pregnancies with trisomy 18 found reduced levels in the maternal serum, and we examine herein the potential of ADAM12 as a marker of trisomy 18 in both the first and second trimester of pregnancy.

MATERIALS AND METHODS

The concentration of ADAM12 was determined by a time-resolved immunofluorometric assay in 132 first and 12 second trimester cases of trisomy 18, and 389 first and 341 second trimester gestational age-matched control pregnancies. Medians of normal pregnancies were established by polynomial regression and used to determine the population distribution parameters for the trisomy 18 and control groups. Correlation with previously established pregnancy-associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin (beta-hCG) multiples of the median (MoMs) and nuchal translucency thickness (NT) MoM were determined and used to model the performance of first trimester screening with ADAM12 in combination with other first trimester markers.

RESULTS

The maternal serum concentration of ADAM12 in the first trimester was significantly reduced with a median MoM of 0.829 (p < 0.001) and a mean log10 MoM SD of 0.2663 compared to 0.3353 in the controls. In the second trimester small series ADAM12 was significantly increased with a median MoM of 2.09 (p = 0.001) and a mean log10 MoM SD of 0.2607 compared to 0.4318 in controls. There was a significant correlation of ADAM12 MoM with gestational age (r = 0.510) in trisomy 18 cases, and the median MoM increased from 0.51 at 10 weeks to 1.28 at 13 weeks and 2.09 across the 14-18 week window. ADAM12 was correlated with PAPP-A (r = 0.1918) in the first trimester of cases with trisomy 18 but less so with NT (r = 0.1594) and free beta-hCG (r = 0.0938). Modeled detection rates incorporating ADAM12, free beta-hCG, and NT were 92% at 1% false positive rate (88% at 0.5%) A combination of all four markers had a detection rate of 96.5% at a false positive rate of 1% (95% at 0.5%).

CONCLUSION

ADAM12 may be a useful addition to early screening for trisomy 18 alongside other chromosomal anomalies, particularly if biochemical screening can occur before 10 weeks.

Performance of free β-human chorionic gonadotrophin (free β-hCG) and pregnancy associated plasma protein-A (PAPP-A) analysis between Delfia Xpress and AutoDelfia systems in The Netherlands

: The VU University Medical Center (VUmc) was the first hospital in the Netherlands to introduce the Delfia Xpress for the analysis of free β-human chorionic gonadotrophin (β-hCG) and pregnancy associated plasma protein-A (PAPP-A) in the first trimester screening program for Down syndrome. Since then, others have implemented this system. In this study, we tested the equality of measurements for free β-hCG and PAPP-A between Delfia Xpress systems and one AutoDelfia system.

: A total of 40 serum samples were aliquoted and stored at –20°C. Samples were analyzed by six Delfia Xpress systems and one AutoDelfia system over a time period of 2 years.

: The relationships between free β-hCG and PAPP-A were excellent for the different Delfia Xpress systems (r>0.99, p<0.0001). For PAPP-A, the agreement between the main system at VUmc and five other systems was linear with slopes between 0.99 and 1.06. Similarly, agreement for free β-hCG was linear with slopes between 0.99 and 1.09. Likewise, agreement for PAPP-A and free β-hCG was excellent for the AutoDelfia vs. the main Delfia Xpress at the VUmc (r>0.99, p<0.0001). For both PAPP-A and free β-hCG, the relationships were linear with slopes of 1.08 and 1.07.

: We demonstrate an excellent agreement for the analysis of PAPP-A and free β-hCG between Delfia Xpress systems and one AutoDelfia system.

Clin Chem Lab Med 2009;47:222–6.

Biochemical screening for Down’s syndrome in the first trimester of pregnancy

Down’s syndrome (DS) is the commonest single cause of severe mental retardation and accounts for just under a third of all cases. Until the late 1980’s population screening was based on offering amniocentensis to older women. This made little impact on the prevalence of DS because the majority (approximately 70%) of babies with DS are born to women under the age of 35 (Figure 1).

Meta-analysis of first trimester Down syndrome screening studies: free beta-human chorionic gonadotropin significantly outperforms intact human chorionic gonadotropin in a multimarker protocol

OBJECTIVE

The purpose of this study was to compare free beta and intact human chorionic gonadotropin in first trimester screening with pregnancy-associated plasma protein-A and nuchal translucency.

STUDY DESIGN

A Monte Carlo simulation trial was conducted based on a literature review of the PUBMED database (1966 to November 2005).

RESULTS

In younger patients (< 35 years), detection of Down syndrome increased by 4, 5, 6, and 7 percentage points when free beta was added to pregnancy-associated plasma protein-A and nuchal translucency compared with 0, 0, 2, and 4 percentage points for intact human chorionic gonadotropin at 9-12 weeks' gestation, respectively. In advanced maternal age patients (> or = 35), inclusion of free beta-human chorionic gonadotropin reduced the false-positive rate by 2.5, 3.1, 3.8, and 4.4 percentage points compared with 0.1, 0.3, 1.0, and 2.2 percentage points for intact human chorionic gonadotropin at 9-12 weeks, respectively.

CONCLUSION

The results of our analysis suggest that in a first-trimester Down syndrome screening protocol free beta-human chorionic gonadotropin achieves higher sensitivity and lower false-positive results than intact human chorionic gonadotropin . Moreover, intact human chorionic gonadotropin does not add substantially to screening performance until the end of the first trimester.

What's new in...obstetrics and gynaecology

This article outlines some recent advances in both obstetrics and gynaecology. In obstetrics, the new screening tests for Down's syndrome and the introduction of computer analysis of the fetal ECG are discussed. Cervical screening and the role of human papilloma virus detection is examined and advances in the non-surgical management of menorrhaghia and improvements in the management of urinary stress incontinence are also reviewed.

An update on antenatal screening for Down's syndrome and specific implications for assisted reproduction pregnancies

Since the introduction of antenatal serum screening for Down's syndrome (DS) more than two decades ago, several screening approaches have been utilized in routine clinical practice. The current DS screening strategies involve mid-trimester serum biochemistry tests, first trimester tests combining sonographic markers and serum biochemistry and integration of first and second trimester markers. In this review, we evaluate the performance of DS screening strategies according to the Serum, Urine and Ultrasound Screening Study (SURUSS), the First and Second Trimester Evaluation of Risks (FASTER) Trial and the Serum Biochemistry and Fetal Nuchal Translucency Screening (BUN) Study. We also evaluate the performance of first trimester screening in studies and meta-analyses by other groups. Specific issues related to assisted reproduction technology (ART) pregnancies are also addressed in this review.

Higher Median Levels of Free β-hCG and PAPP-A in the First Trimester of Pregnancy in a Chinese Ethnic Group

OBJECTIVE

To study the effect of ethnic Chinese on the medians of free beta-hCG and PAPP-A in the first trimester of pregnancy.

METHODS

The data of 943 women undergoing first trimester combined screening for fetal Down syndrome were analysed to derive the Chinese-specific medians. The calculated risk of Down syndrome based on these Chinese-specific medians was compared with that based on the original algorithm of the Fetal Medicine Foundation (FMF).

RESULTS

The maternal serum levels of multiples of median of free beta-hCG and PAPP-A were significantly higher among the Chinese than among the Caucasians. The weight-adjusted gestation-specific medians were developed. Without adjustment for ethnicity, the original FMF algorithm underestimated the risk of Down syndrome by a median of 1%. Adjustment by ethnicity increased the false-positive rate by 10% (from 5.3 to 5.9%).

CONCLUSION

Ethnic Chinese have a significantly higher maternal serum level of free beta-hCG and PAPP-A in the first trimester, which could not be explained by differences in maternal weight. Adjustment for ethnicity may be necessary for these biochemical markers in a first trimester screening program.

A link between high serum levels of human chorionic gonadotrophin and chorionic expression of its mature functional receptor (LHCGR) in Down's syndrome pregnancies

Human chorionic gonadotrophin (hCG) is released from placental trophoblasts and is involved in establishing pregnancy by maintaining progesterone secretion from the corpus luteum. Serum hCG is detected in the maternal circulation within the first 2-3 wks of gestation and peaks at the end of the first trimester before declining. In Down's syndrome (DS) pregnancies, serum hCG remains significantly high compared to gestation age-matched uncompromised pregnancies. It has been proposed that increased serum hCG levels could be due to transcriptional hyper-activation of the CGB (hCG beta) gene, or an increased half life of glycosylated hCG hormone, or both. Another possibility is that serum hCG levels remain high due to reduced availability of the hormone's cognate receptor, LHCGR, leading to lack of hormone utilization. We have tested this hypothesis by quantifying the expression of the hCG beta (CGB) RNA, LHCGR RNA and LHCGR proteins in chorionic villous samples. We demonstrate that chorionic expression of hCG beta (CGB) mRNA directly correlates with high serum hCG levels. The steady-state synthesis of LHCGR mRNA (exons 1-5) in DS pregnancies was significantly higher than that of controls, but the expression of full-length LHCGR mRNA (exons 1-11) in DS was comparable to that of uncompromised pregnancies. However, the synthesis of high molecular weight mature LHCGR proteins was significantly reduced in DS compared to uncompromised pregnancies, suggesting a lack of utilization of circulating hCG in DS pregnancies.

Improved first-trimester Down syndrome screening performance by lowering the false-positive rate: a prospective study of 9941 low-risk women

OBJECTIVE

To determine the performance of screening for Down syndrome (DS) and other major chromosomal abnormalities using nuchal translucency (NT), free beta-human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A) in a prospective study of a non-selected population.

METHODS

Of 9941 women with an early ultrasound examination, NT was measured in 8622 singleton pregnancies with a gestational age between 10 + 3 and 13 + 6 weeks. beta-hCG and PAPP-A were analyzed in 6441 cases. Detection rates (DR) and false-positive rates (FPR) for the NT screening, the double test (beta-hCG and PAPP-A) and the combined test (NT and the double test) were calculated using a 1 : 250 cut-off.

RESULTS

NT could be measured in 97.5% of cases. The DR for DS with NT screening alone was 75% with a FPR of only 1.8%. The double test detected 73% and the combined test 91%, for FPRs of 8.8% and 2.1%, respectively. We detected 80% of fetuses with other major chromosomal abnormalities with a combination of NT screening and other ultrasound findings. Low beta-hCG and PAPP-A values (below 0.4 MoM) were observed in 0.5% of the women including all cases of triploidy and trisomy 18 and 13.

CONCLUSIONS

The performance of a screening strategy for DS using a combination of NT and the double test was superior to that using either NT or the double test alone due to a very low FPR and a higher DR.

First- and midtrimester Down syndrome screening and detection

Overall, Down syndrome detection capabilities have improved remarkably over the last 2 decades. Widely practiced first-trimester screening and less extensively elevated midtrimester urine screening promise even greater accuracy than was available a decade ago. Recently, the combination of first- and second-trimester screening has been reported to enhance discrimination of the Down syndrome fetus from normal cases. Although the advances are welcome, they present the significant prospect of multiple competitive algorithms with the risk of confusing patients, practitioners, and health care planners. The need for reasonable consensus has never been more pressing.

First-trimester combined ultrasound and biochemical screening for Down syndrome in routine clinical practice

OBJECTIVES

To assess the effectiveness of combined ultrasound and biochemical (CUB) screening for chromosome abnormalities in singleton pregnancies in a routine antenatal clinic and laboratory setting.

METHODS

Women whose pregnancies fell within the gestational age range of 11 to 14 weeks by ultrasound assessment were offered CUB screening on the basis of measurement of nuchal translucency (NT), maternal serum free beta-human chorionic gonadotrophin (FbetahCG) and pregnancy-associated plasma protein A (PAPP-A). NT measurements were obtained using a standardised method defined by the Fetal Medicine Foundation and FbetahCG, and PAPP-A were measured using the DELFIA immunoassay system. Each screening marker measurement was converted to a multiple of the appropriate gestational median and a risk was derived using previously published parameters for each marker in chromosomally abnormal and unaffected pregnancies. A combined risk of Down syndrome and of trisomy 18/13, incorporating the maternal age risk, was calculated for all women. Invasive diagnostic testing was offered to women whose combined risk exceeded the cut-off risk of 1 in 250 (term).

RESULTS

Five thousand and eighty-four women accepted a first-trimester screening test for Down syndrome, representing 75% of the eligible booking population. Out of the population eligible for CUB screening at the time of booking, NT measurements were obtained from 93% at the first clinic visit and 7% had to return for a second attempt. After excluding women who defaulted on a return visit, satisfactory NT measurements were obtained in 99.5% of pregnancies. Fifteen cases of Down syndrome and eleven pregnancies with other chromosome abnormalities were ascertained. The detection rate for Down syndrome was 93% (14/15) at a false-positive rate of 5.9% and for all chromosome abnormalities it was 96% (25/26) at an overall false-positive rate of 6.3%.

CONCLUSIONS

CUB screening offers a significant improvement in sensitivity over second-trimester biochemical screening and is deliverable within a routine prenatal clinical setting.

Prenatal screening for Down syndrome: current and future methods

Second-trimester serum screening for Down syndrome has had a relatively long clinical life, beginning in the mid-1980s and continuing to the present day. In the past few years, however, new screening methods that involve testing just a few weeks earlier and the integration of first-trimester and second-trimester markers have been proposed and are being used. These improved methods have begun the transition to better and, hopefully, safer prenatal screening. In the past, as many as 1 in 10 pregnant women learned that they were at increased risk of having a baby with a serious birth defect and had to decide whether to have an invasive diagnostic procedure. Now, screening methods are at the point where as few as 1 in 50 or 1 in 100 pregnant women are found to be at increased risk. The ultimate goal in screening is to make noninvasive testing methods so safe that only those few women who are found to be at the very highest risk will need to face the uncertainty of invasive procedures. In the next few years, that goal will probably be achieved.

Integrated ultrasound and biochemical screening for trisomy 21 using fetal nuchal translucency, absent fetal nasal bone, free beta-hCG and PAPP-A at 11 to 14 weeks

BACKGROUND

Screening for trisomy 21 by a combination of maternal age, fetal nuchal translucency (NT) thickness and maternal serum free beta-hCG and pregnancy-associated plasma protein-A (PAPP-A) at 11 to 14 weeks of gestation is associated with a detection rate of 90% for a false-positive rate of 5%. Recent evidence suggests that in about 70% of fetuses with trisomy 21, the nasal bone is not visible at the 11th- to 14th-week scan (Cicero et al., 2001). The aim of this study was to examine whether fetal NT thickness and the level of maternal serum biochemical markers is independent of the presence or absence of the nasal bone, and to estimate the performance of a screening test that integrates the two sonographic and the two biochemical markers.

METHODS

This was a retrospective case-control study comprising 100 trisomy 21 and 400 chromosomally normal singleton pregnancies at 11 to 14 weeks of gestation. Ultrasound examination was carried out for measurement of fetal NT and assessment of the presence or absence of the fetal nasal bone. Maternal serum free beta-hCG and PAPP-A were measured using the Kryptor rapid random-access immunoassay analyser (Brahms Diagnostica GmbH, Berlin). The distribution of fetal NT, maternal serum free beta-hCG and PAPP-A in trisomy 21 fetuses with absent and present nasal bone was examined.

RESULTS

The nasal bone was absent in 69 and present in 31 of the trisomy 21 fetuses. There were no significant differences in median maternal age, median gestational age, NT delta, free beta-hCG MoM and PAPP-A MoM in trisomy 21 fetuses with and without a visible nasal bone. For a false-positive rate of 5%, it was estimated that screening with the four markers in combination with maternal age would be associated with a detection rate of 97%. For a false-positive rate of 0.5%, the detection rate was 90.5%.

CONCLUSIONS

An integrated sonographic and biochemical test at 11 to 14 weeks can potentially identify about 90% of trisomy 21 fetuses for a false-positive rate of 0.5%.

Human chorionic gonadotropin free beta-subunit in the human seminal plasma: a new marker for spermatogenesis?

In the past 20 years, several factors were detected in the human seminal plasma and proposed as markers for spermatogenesis. Human chorionic gonadotropin (hCG) and its beta-subunit were therefore investigated, and their seminal levels were found to be higher than those detected in the serum and to correlate with sperm parameters.

OBJECTIVE

We designed a retrospective study to determine the suitability of hCG free beta-subunit concentration in the seminal plasma of fertile and infertile male patients as marker of spermatogenesis.

STUDY DESIGN

A total of 79 infertile male patients were divided into four groups by their semen analysis results (group 1 [n=8]: azoospermia; group 2 [n=21]: severe oligozoospermia; group 3 [n=40]: oligoasthenospermia (OAS); group 4 [n=10]: asthenospermia) and 10 healthy volunteers of proven fertility were evaluated.

RESULTS

The hCG free beta-subunit levels in the seminal plasma were found to be significantly higher (P<0.0001) in the control group in respect to those assayed in the infertile patients and showed a correlation with sperm count (r=0.5) and total motile sperm density (r=0.5). Twenty-five patients were on treatment with oral Mesterolone (100mg daily) plus Tamoxifen (20mg daily) for 3-6 months. Apart from a significant improvement (P<0.05) in sperm morphology, no significant changes in sperm count and motility were observed after the treatment in all the patients. In the seminal plasma of 10 patients who showed a significant increase in sperm count, hCG free beta-subunit levels were found to be significantly higher compared to those detected in the remaining patients (P<0.01). In all patients, these levels remained unchanged after the treatment.

CONCLUSIONS

The evidence regarding the positive correlation between hCG free beta-subunit levels in the seminal plasma and sperm concentration is consistent with the previous results regarding hCG levels. A previous study demonstrated that testosterone levels in seminal plasma correlated with sperm concentrations; from the same evidence regarding hCG we hypothesize that seminal plasma testosterone and hCG levels are correlated. Thus, hCG may play a paracrine role in the intratesticular regulation of testosterone secretion.

Combined ultrasound and biochemical screening for Down's syndrome in the first trimester: a Scottish multicentre study

OBJECTIVE

To evaluate the use of ultrasound measurements of fetal nuchal translucency (NT) obtained in a routine antenatal clinic setting in combination with appropriate biochemical markers as a first trimester screening test for Down's Syndrome.

DESIGN

Multicentre observational study.

SETTING

Fifteen Scottish maternity units.

POPULATION

Pregnant women (n = 17,229) attending routine antenatal clinics at 10-14 weeks of gestation.

METHODS

NT measurements were attempted in all women along with the measurement of maternal serum free beta human chorionic gonadotrophin (F beta hCG) and pregnancy-associated plasma protein-A (PAPP-A). All results were converted to multiples of the appropriate gestational median (MoM) and using a statistical model the risk of an affected pregnancy was derived. No results were given to participating women but all were offered routine second trimester biochemical screening. All cases of Down's Syndrome within the study group were ascertained and the detection rate for each marker was estimated.

MAIN OUTCOME MEASURES

Success rate of obtaining NT measurements and overall effectiveness of ultrasound and biochemical markers individually and in combination for the detection of Down's Syndrome pregnancies.

RESULTS

NT measurements were obtained in 72.9% of women and blood samples in 98.4%. Forty-five cases of Down's Syndrome were ascertained (2.6/1,000). NT measurements were obtained in 37 cases (median NT 1.65 MoM), blood samples in 42 cases and both NT and blood in 34 cases. In combination with the a priori maternal age risk, observed detection rates at a 5% false positive rate were 20/37 (54%) for NT, 23/42 (55%) for F beta hCG and PAPP-A and 28/34 (82%) for a combination of NT, F beta hCG and PAPP-A using a cutoff risk of 1:250. The effect of failing to obtain NT measurements in all cases reduces the overall detection rate to 62% (i.e. 28/45) if the entire series of affected pregnancies within the study group is considered.

CONCLUSIONS

NT in combination with appropriate serum markers has the potential to detect over 80% of Down's Syndrome fetuses in early pregnancy. However, NT measurement is highly operator-dependent. It requires training, external quality control and adequate time to allow accurate measurement, otherwise suboptimal performance will result.

Accuracy of Down syndrome risks produced in a first-trimester screening programme incorporating fetal nuchal translucency thickness and maternal serum biochemistry

Over the past three years approximately 12 000 women have been screened in the first trimester through our OSCAR programme, which utilizes fetal NT and maternal serum free beta-hCG and PAPP-A. During this time 30 cases of Down syndrome were identified either prenatally or postnatally. Using an established procedure the accuracy of predicted risk for Down syndrome was assessed in a population of 30 cases of Down syndrome and 11 758 unaffected pregnancies. The correlation between predicted risk and prevalence of Down syndrome was very high (r=0.9995). It is concluded that risks produced by the Fetal Medicine Foundation combined risk algorithm agree very closely with Down syndrome prevalence and can be used with confidence when counselling women of their risk.

First trimester maternal serum placenta growth factor (PIGF)concentrations in pregnancies with fetal trisomy 21 or trisomy 18

Placenta growth factor (PIGF), an angiogenic factor belonging to the vascular endothelial growth factor family, pregnancy-associated plasma protein A (PAPP-A) and free beta-human chorionic gonadotrophin (beta-hCG) were measured in maternal serum from 45 pregnancies with trisomy 21, 45 with trisomy 18 and 493 normal controls at 10-13 completed weeks of gestation. In the normal pregnancies maternal serum PIGF levels increased exponentially with gestation. The median multiple of the median (MoM) PIGF concentration in the trisomy 21 group (1.26 MoM) was significantly higher (p<0.0001) than in the control group (1.00 MoM). In the trisomy 18 group the median PIGF was lower (0.889 MoM) but this did not quite reach significance (p=0.064). The corresponding median MoM values for PAPP-A were 1.00 MoM for the controls, 0.49 MoM for trisomy 21 and 0.16 MoM for trisomy 18. The median MoM values for free beta-hCG were 1.00 MoM for the controls, 2.05 MoM for trisomy 21 and 0.38 MoM for trisomy 18. In the control group there was a small but significant correlation of PIGF with free beta-hCG (r=+0.1024) and PAPP-A (r=+0.2288). In the trisomy 18 group there was a significant association between PIGF and free beta-hCG (r=+0.2629) but not with PAPP-A (r=+0.0038). In the trisomy 21 group there was a small but significant association with PAPP-A (r=+0.1028) but not with free beta-hCG (r=+0.0339). The separation of affected and unaffected pregnancies in maternal serum PIGF is small, and therefore it is unlikely that measurement of PIGF would improve screening for these abnormalities provided by the combination of fetal nuchal translucency and maternal serum PAPP-A and free beta-hCG.

First-trimester biochemical screening for Down syndrome

Of all markers evaluated for first-trimester biochemical screening for Down syndrome (DS), PAPP-A and free beta-hCG emerged as the most predictive. The combined test uses these markers in conjunction with nuchal translucency measurements, and is estimated to achieve a DS detection rate of 80% to 85% at a 5% false-positive rate. The integrated test, combining first-trimester sonographic and biochemical markers with second-trimester markers, provides a single estimate of a patients DS risk, and may yield a DS detection rate of 94% at a 5% false-positive rate. The acceptability and feasibility of this test, however, remain to be proved.

Maternal serum levels of dimeric inhibin A in pregnancies affected by trisomy 21 in the first trimester

Dimeric inhibin A was measured in maternal serum samples from 45 pregnancies affected by trisomy 21 and 493 samples from unaffected pregnancies at 10-14 weeks of gestation. Inhibin A levels in affected pregnancies were compared with levels of free beta-hCG and PAPP-A in the same series. In the trisomy 21 group, the median multiple of the median (MoM) inhibin A was not significantly elevated (1.28 vs 1.00) with only 15.5% being above the 95th centile. In contrast, the median MoM free beta-hCG was significantly increased (2.05 vs 1.00) with 36% above the 95th centile and PAPP-A was significantly reduced (0.49 vs 1.00) with 42% below the 5th centile. Inhibin A levels in the trisomy 21 group were significantly correlated with gestational age such that median levels rose from 1.04 at 11 weeks to 1.30 at 12 weeks and 1.67 at 13 weeks. These findings suggest that first trimester biochemical screening for trisomy 21, which is currently optimised using maternal serum free beta-hCG and PAPP-A and fetal nuchal translucency, will not benefit from the inclusion of inhibin A.

Maternal serum levels of total activin-A in first-trimester trisomy 21 pregnancies

Maternal serum total activin-A concentration was measured in 45 pregnancies affected by trisomy 21 and 493 control unaffected pregnancies at 10-14 weeks of gestation. In the trisomy 21 pregnancies total activin-A concentration was significantly higher (1.36 MoM of the unaffected pregnancies) and in 16% of cases the level was above the 95th centile of normal. The log10 SD for the control group and the trisomy 21 group were 0.17 and 0.22, respectively. The median pregnancy associated plasma protein-A (PAPP-A) in this trisomy 21 series was 0.49 and for free beta-hCG was 2.05. In the trisomy group there were significant positive associations between total activin-A and PAPP-A (0.6071) and free beta-hCG (0.4255). The low median difference and the high overlap in values between trisomic and unaffected pregnancies make total activin-A of little practical use in first-trimester screening for trisomy 21.

Screening for triploidy by fetal nuchal translucency and maternal serum free beta-hCG and PAPP-A at 10-14 weeks of gestation

In 25 cases of triploidy at 10-14 weeks of gestation, compared with 947 controls, the median multiple of the median (MoM) fetal nuchal translucency (NT) thickness was significantly increased (1.89 MoM), and maternal serum total and free beta-human chorionic gonadotrophin (hCG) were increased (3.13 MoM and 4.59 MoM respectively), alpha fetoprotein (AFP) was increased (2.14 MoM), and pregnancy associated plasma protein A (PAPP-A) was decreased (0.12 MoM). There are two types of triploidy. In type I, where the additional chromosome set is of paternal origin, the placenta is partially molar and the fetus is relatively well-grown. Type II, where the extra chromosome set is of maternal origin, is characterized by a small normal looking placenta and severe asymmetrical fetal growth restriction. In type I triploidy there was increased fetal NT (2.76 MoM), maternal serum total hCG (4.91 MoM), free beta-hCG (8.04 MoM), and AFP (3.22 MoM), and mildly decreased PAPP-A (0.75 MoM). In type II triploidy fetal NT was not increased (0.88 MoM), and there was a decrease in maternal serum total hCG (0.16 MoM), free beta-hCG (0.18 MoM), PAPP-A (0.06 MoM) and AFP (0.77 MoM). We conclude that a large proportion of triploidy cases of both phenotypes could be identified in the first trimester using NT, maternal serum free beta-hCG and PAPP-A with a combination of trisomy 21 risk and an atypicality approach.

Is maternal serum total hCG a marker of trisomy 21 in the first trimester of pregnancy?

In a study of 130 first trimester cases of trisomy 21 and 959 controls we have shown that the median MoM for alpha-fetoprotein (AFP) is lower (0.82) and that for total human chorionic gonadotrophin (hCG) is higher (1.31) than in the control group. For AFP 15.3% of cases were below the 5th centile and for total hCG 19. 8% were above the 95th centile. The median shift observed for AFP and total hCG is poorer than that for pregnancy associated plasma protein-A (PAPP-A) or free beta-hCG and together with maternal age, AFP and total hCG could only be expected to detect 40% of cases. In combination with PAPP-A, total hCG would identify 52% of cases, somewhat less than the 67% observed with free beta-hCG and PAPP-A. However, we have demonstrated for total hCG a significant temporal change in median MoM with gestational age. Before 70 days the median MoM was less than 0.5, between 70 and 83 days this increased to 1.13, and between 84 and 97 days this increased to 1.52. This median shift has significant implications for interpreting previous studies and even more significant implications for detection rates. When population parameters specific to the gestational age in question are used, detection rates with total hCG and PAPP-A increase from 47% at 70-83 days to 60% at 84-97 days. This observation explains much of the confusion around total hCG in the first trimester and shows the importance of selecting analyte pairs and population parameters appropriate to the time in gestation when screening is performed.

Screening for trisomy 18 by fetal nuchal translucency and maternal serum free beta-hCG and PAPP-A at 10-14 weeks of gestation

In a study of 50 cases of trisomy 18 compared with 947 controls we have found the median multiple of the median (MoM) of maternal serum free beta human chorionic gonadotrophin to be significantly decreased (0.281 MoM) in samples collected between the 10th and 14th week of gestation. Similarly, maternal serum pregnancy associated plasma protein A (PAPP-A) levels are also decreased (0.177 MoM), whilst the median nuchal translucency is significantly higher (3.272 MoM). Free beta-hCG MoM was less than the 5th centile of normal in 64 per cent of cases of trisomy 18 and for PAPP-A was less than the 5th centile in 78 per cent of cases. Also, in 78 per cent of cases the nuchal translucency was above the 95th centile. When combined together in a multivariate algorithm with maternal age, we predict that 89 per cent of cases of trisomy 18 could be detected at a 1 per cent false-positive rate. We conclude that specific trisomy 18 risks should be part of developing risk algorithms combining maternal serum biochemistry and nuchal translucency for use in first trimester screening alongside those for trisomy 21.