Prenatal screening for trisomy 18 with free beta human chorionic gonadotrophin as a marker

Microarray analysis: First-trimester maternal serum free β-hCG and the risk of significant copy number variants

OBJECTIVE

To determine whether abnormal levels of first-trimester maternal serum free β-hCG and PAPP-A are associated with significant copy number variants (CNVs) on chromosomal microarray analysis (CMA).

METHODS

Retrospective cohort of singleton prenatal CMA studies (n = 2880). Cases with an abnormal karyotype, benign familial or de novo variants, and absence of heterozygosity were excluded. The prevalence of abnormal serum analytes was compared between patients with significant CNVs (n = 56) and those with normal CMA (n = 884). Odds ratios (ORs) and 95% confidence intervals (CI) were calculated using Fisher's exact test. Mantel-Haenszel method was utilized to adjust ORs for prenatal diagnostic procedure type and indications for testing. Statistical significance was determined as P value < 0.05.

RESULTS

Abnormally low serum free β-hCG (≤0.45 MoM) was associated with an increased risk of significant CNVs (OR 3.53, 95% CI, 1.25-8.66, P < 0.01). This association remained significant after adjusting for abnormal nuchal translucency and advanced maternal age (AMA) (adjusted OR 3.04, 95% CI, 1.05-7.48, P < 0.05) or procedure type and AMA (adjusted OR 3.21, 95% CI 1.13-8.16, P < 0.05). The associations of abnormally high serum free β-hCG, low PAPP-A, and high PAPP-A with significant CNVs were not statistically significant.

CONCLUSION

Low first-trimester serum β-hCG is associated with an increased risk of significant CNVs on CMA.

Screening for chromosomal abnormalities using combined test in the first trimester of pregnancy

Objective

This study was designed to review the screening performance of combined test at the Ewha Womans University Mokdong hospital.

Methods

All women admitted for routine antenatal care between January 1st 2008 and December 31st 2012 with a known pregnancy outcome were included in this study, totaling 1,156 women with singleton pregnancies presenting at 10 to 13 weeks of gestation. Women were offered screening using a combination of maternal serum pregnancy-associated plasma protein-A, free β-human chorionic gonadotropin and fetal nuchal translucency thickness. Those with an estimated risk of ≥1 in 250 of carrying a fetus with trisomy 21 or ≥1 in 300 risk of trisomy 18 were offered genetic counseling with the option of an invasive diagnostic test.

Results

The median of gestational age was 11+3 weeks, the median of crown-rump length was 47.1 mm, and the median age of the women was 31 years. The detection rate was 80% for trisomy 21 (4 of 5) and 100% for trisomy 13 and 18 (all 2). The false-positive rate was 7.73% for trisomy 21 and 1.21% for trisomy 18.

Conclusion

This study was the first large population study performed with the aim of analyzing the performance of the combined test in Korea. This study demonstrated that the detection rates and other figures of the first trimester combined test are comparable to the results reported in other papers worldwide. Consequently, if strict conditions for good screening outcomes are achieved, the first trimester combined test might well be the earliest detectable screening, improving detection rates without increasing karyotyping or economic and other implications that inevitably ensue.

Detection of trisomy 18 and trisomy 13 using first and second trimester Down's syndrome screening markers

Objective

To estimate the detection rates (DRs) and false-positive rates (FPRs) in the incidental identification of trisomy 18 (T18) and trisomy 13 (T13) as part of antenatal screening for Down's syndrome (DS) using the Combined, Quadruple and Integrated test markers.

Methods

Screening marker levels on 224 T18 and 67 T13 pregnancies screened for DS were evaluated. Estimated means, standard deviations and correlation coefficients were used with published estimates for unaffected pregnancies to derive detection algorithms for the two disorders. DRs and FPRs of the algorithms were estimated using Monte Carlo simulation.

Results

In T18 and T13 pregnancies first trimester nuchal translucency was raised, free β-human chorionic gonadotrophin (hCG) and pregnancy associated plasma protein-A reduced. In T18 pregnancies second trimester alphafetoprotein, unconjugated oestriol and free β-hCG were reduced. In T13 pregnancies second trimester inhibin-A was raised. These markers specified T18 and T13 algorithms. The DS Combined test algorithm detected 42% of T18 and 59% of T13 (2.00% FPR); 88% and 74% by adding the T18 Combined test algorithm (2.17% FPR) and 89% and 75% by further adding the T13 Combined test algorithm (2.19% FPR). The corresponding detection rates for the Quadruple test were: 2% and 17% (2.00% FPR), 55% and 17% (2.16% FPR) and 55% and 19% (2.28% FPR), and for the Integrated test were: 40% and 64% (2.00% FPR), 92% and 65% (2.12% FPR) and 92% and 72% (2.18% FPR).

Conclusions

Antenatal screening for DS detects about 40% of T18 and about 60% of T13 pregnancies. The addition of a T18 algorithm substantially increases the detection of both trisomies with a small increase in the FPR. The further addition of a T13 algorithm results in a small increase in the detection of T13.

Maternal serum screening for Down syndrome in women aged 40 years and over

Two hundred and thirty-nine women aged 40 years were booked for delivery at Kettering General Hospital from 1992 to 1997. Six women were not eligible for the triple test (TT) as they booked too late. Eighty-eight women declined TT. The reasons were; fear and anxiety about the risk of miscarriage associated with amniocentesis if the test result were a high risk (70.5%), worries about the false negative result associated with the TT (20.5%) and reluctance to terminate the pregnancies if the fetus were abnormal (9%). One hundred and forty-five women (62.2%) elected for TT of whom 91 (62.8%) had received a high risk results. Of the women who received a high-risk result 61/91 (67%) had an amniocentesis. The study provides an accurate probability of receiving a high risk TT screening in women aged 40 years and highlights the need for a more sensitive screening test or a less invasive diagnostic test for the detection of Down syndrome.

Aneuploidy screening in the first trimester

This article reviews the performance of first trimester screening for chromosomal anomalies using various combinations of ultrasound and maternal serum biochemical modalities. Detection rates in excess of 90% can be routinely achieved for Trisomy 21, Trisomy 13, Trisomy 18 using a combination of fetal nuchal translucency (NT) thickness and maternal serum free ss-hCG and PAPP-A at 11 + 0 to 13 + 6 weeks of gestation.

Low maternal serum concentrations of human chorionic gonadotropin as part of the triple test screening: a follow-up study

OBJECTIVE

To determine whether low maternal serum concentrations of human chorionic gonadotropin (hCG) were associated with poor pregnancy outcome.

METHODS

Between 1999 and 2000, 20,880 women underwent triple test screening in our hospital. The levels of hCG were detected by fluorescent immunoassay. Low hCG levels (< or = 0.20 MoM in our center) were considered to be a marker for increased risk for trisomy 18 or adverse pregnancy outcome. Each patient completed a questionnaire regarding fetal karyotype, complications of pregnancy and pregnancy outcome.

RESULTS

Low maternal serum concentrations of hCG were detected in 119 pregnancies (0.57%). Of these, 19 (16%) were found to be missed abortions. The distribution of the remaining 100 cases was as follows: 72% had an isolated low hCG level, 24% had a low hCG level and a combination of hCG + alpha-fetoprotein < 0.80 MoM, and 4% had a low hCG level and a combination of hCG + unconjugated estriol < 0.80 MoM. No trisomy 18 or other chromosomal abnormalities were detected in our patient population. However, there were perinatal complications.

CONCLUSION

Based on our screened population, a combination of multiple analytes seemed to be a better marker than an isolated finding of low maternal serum concentrations of hCG with regards to abnormal fetal karyotype, specifically trisomy 18, although it did determine a high-risk group in terms of complications of pregnancy.

Second trimester two-step trisomy 18 screening using maternal serum markers

Trisomy 21 maternal serum marker screening has led to screening for other anomalies, including trisomy 18. Trisomy 18 is generally prenatally diagnosed because of major morphological defects. However, in up to 30% of cases ultrasound signs are unclear, and in most cases diagnosis is performed late in pregnancy. Of the different maternal serum markers, PAPP-A is now considered as the best for trisomy 18 screening. However, pregnancy-associated plasma protein A (PAPP-A) is of value in first trimester screening for trisomy 21, but not in the second trimester. We therefore propose a two-step screening strategy. Based on 45 trisomy 18 cases, we confirm the values of alpha-fetoprotein (AFP) (median 0.61 MoM), free beta-human chorionic gonadotrophin (beta-hCG) (median 0.24 MoM) and of PAPP-A (median 0.08 MoM). In the first step, a 0.5 MoM cut-off for AFP or for free beta-hCG resulted in detection of 37/45 trisomy 18 cases (82%) with a 10% false-positive rate. The second step consisted of the measurement of PAPP-A for all these false-positive cases. Using a PAPP-A cut-off of 0.5 MoM, all the 37 trisomy 18 cases were detected, but now with a 0.1-0.2% false-positive rate. Amniocentesis was only offered to these few patients. This two-step second trimester screening will be of value for patients who have not been included in first trimester screening based on nuchal translucency (NT) measurement combined with the first trimester markers, PAPP-A and free beta-hCG.

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.

Maternal serum activin A and inhibin A in trisomy 18 pregnancies at 10-14 weeks

In 45 cases of trisomy 18 and 493 control pregnancies at 10-14 weeks of gestation, maternal serum inhibin A, total activin A, free beta-hCG and PAPP-A were measured. In the trisomy 18 pregnancies the median values were 0.74 MoM for inhibin A, 1.23 MoM for activin A, 0.38 MoM for free beta-hCG and 0.16 MoM for PAPP-A. The degree of deviation from normal in the levels of inhibin and activin is small in comparison with free beta-hCG and PAPP-A and they are therefore unlikely to be of value in improving the sensitivity of 90% for a 1% false-positive rate achieved by screening with fetal nuchal translucency and maternal serum free beta-hCG and PAPP-A.

One stop clinic for assessment of risk for fetal anomalies: a report of the first year of prospective screening for chromosomal anomalies in the first trimester

OBJECTIVE

To evaluate the introduction of a one stop multidisciplinary clinic for screening for fetal chromosomal abnormalities in the first trimester by a combination of maternal serum biochemistry and ultrasonography providing a risk of chromosomal abnormalities within a one hour clinic visit.

DESIGN

One year retrospective review of screening performance.

POPULATION

All women attending for routine antenatal care. The population included 4,190 singleton pregnancies in women of all ages screened between 10 weeks and 3 days and 13 weeks and 6 days of gestation between the periods 1 June 1998 and 31 May 1999 in a district general hospital antenatal clinic.

METHODS

All women booked into the clinic were offered screening by a combination of maternal serum free beta human chorionic gonadotrophin (hCG) and pregnancy associated plasma protein A (PAPP-A) and fetal nuchal translucency thickness. Women at increased risk of carrying a fetus with trisomy 21 or trisomy 18/13 (> or =1 in 300 at sampling) were offered counselling and an invasive diagnostic procedure. Follow up of the outcome of all pregnancies was carried out.

MAIN OUTCOME MEASURES

The detection rate for trisomy 21, trisomy 18/13 and all aneuploides, false positive rate, uptake of screening, uptake of chorionic villus sampling in women identified at increased risk and fetal loss after chorionic villus sampling.

RESULTS

Overall 97.6% of the women (4,088/4,190) accepted first trimester screening. The rate of detection of trisomy 21 was 86% (6/7), for trisomy 18/13 100% (9/9) and for all aneuploides 95% (18/19). Fetal death at presentation was found in 1.6% of pregnancies (69/4,088). Of women who accepted screening, 6.1% (257/4,088) presented too late for fetal nuchal translucency measurement and 6.5% of the women (271/4,088) presented too early. The false positive rate was 6.7% (253/3,762). Uptake of invasive testing was 83% (207/253).

CONCLUSION

First trimester prenatal screening for chromosomal abnormalities using a combination of maternal serum biochemistry and fetal nuchal translucency thickness can achieve detection rates in excess of 90%. These services can be provided in a one stop multidisciplinary clinic.

Ultrasonographic markers for chromosomal abnormalities in women with negative nuchal translucency and second trimester maternal serum biochemistry

OBJECTIVE

To analyze the value of second trimester ultrasound examination among those women whose fetuses were indicated to be at low risk of chromosomal anomalies on the basis of both first trimester nuchal translucency measurement and second trimester biochemical screening.

METHODS

A retrospective study of 5500 pregnancies carried out at the fetal medicine unit, Royal Free Hospital. During a period of over 3 years 5500 pregnancies underwent a first trimester scan and nuchal translucency measurement which enabled the detection of 62% (20 of 32) of all chromosomal anomalies. From the remaining pregnancies that underwent second trimester biochemical screening, 3548 were considered negative (risk < 1:250; using maternal serum free beta human chorionic gonadotrophin and alpha fetoprotein). The ultrasound markers that were examined were: shortened femur length, echogenic bowel, pyelectasis, choroid plexus cysts and echogenic intracardiac foci. The likelihood ratios for chromosomal aneuploides for each of these markers were calculated.

RESULTS

Of the 3548 screen negative pregnancies, 3541 (99.8%) had a normal karyotype. Seven (0.2%) fetuses had an abnormal karyotype including four (0.11%) with trisomy 21, one with trisomy 18 and two with 47XXY. Second trimester ultrasound markers were found in two of the five (40%) with severe chromosomal anomalies compared to 184 of 3541 (5.2%) with normal karyotypes. Detection of one or more ultrasound markers in a screen negative pregnancy increased the possibility of chromosomal aneuploidy and a negative ultrasound decreased the risk by a likelihood ratio of 0.6 (95% confidence interval, 0.3-1.3). The risk was considerably increased when two or more markers were detected and we would recommend karyotyping under these circumstances.

CONCLUSION

This preliminary data indicates a possible role for abnormal ultrasound markers in assessing the risk of chromosomal abnormalities in patients considered to be at low risk by nuchal translucency and serum screening. However analysis of a much larger study group will have to be conducted to assess the significance of individual markers.

Maternal serum screening for trisomy 18: assessing different statistical models to optimize detection rates

We have evaluated three alternative models for trisomy 18 screening using the maternal serum markers alpha-fetoprotein (AFP) and intact human chorionic gonadotrophin (hCG). Using data from 46 affected pregnancies and 48 150 unaffected pregnancies, we calculated distribution parameters for AFP and hCG multiples of the median (MoMs) and the factor comprising AFP MoMxhCG MoM. The trisomy 18 risk at mid-trimester was then calculated using either bivariate analysis of AFP and hCG MoMs or univariate analysis of AFP MoMxhCG MoM. The observed detection rates and positive rates obtained using either published distribution parameters or those derived from the West Midlands population were compared for each model. Using fixed cut-offs for AFP and hCG of 0.66 and 0.40 MoMs resulted in a detection rate of 28.3% for a 0.5% false positive rate (FPR). Using published parameters, the univariate analysis model had a slightly higher detection rate of 32.6% for a 0.5% FPR (cut-off 1:248) compared to the bivariate model which was 28.3% (cut-off 1:239). Locally derived distribution parameters significantly improved the detection rate for the bivariate model for FPRs between 0.4-1.3% but worsened it below 0.4%. For the univariate model there was little difference in detection whether local or published parameters were used. Thus, we have confirmed that trisomy 18 screening using two markers can be a worthwhile addition to Down screening.

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.

Second trimester prenatal screening for Down's syndrome using alpha-fetoprotein and free beta hCG: a seven year review

OBJECTIVE

To determine the value and impact over a seven year period of a second trimester screening programme for trisomy 21 and trisomy 18, using the two maternal serum markers alpha-fetoprotein and free beta human chorionic gonadotrophin.

DESIGN

Retrospective review.

SETTING

A biochemical screening laboratory serving three health districts with three antenatal clinics in both teaching and nonteaching hospitals.

POPULATION

67,904 pregnancies in women of all ages screened between 14 and 22 weeks of gestation between 1 April 1991 and 31 March 1998.

METHODS

All women booked into three major antenatal clinics were offered biochemical screening. Women at increased risk of trisomy 21 or trisomy 18 (> or =1 in 250 at term) were offered an invasive diagnostic procedure. Follow up of the outcome of all pregnancies was performed.

MAIN OUTCOME MEASURES

Detection rate for trisomy 21 and trisomy 18, false positive rates, uptake of screening, uptake of amniocentesis in women identified at increased risk, prevalence of trisomy 21 at birth, detection and false positive rates by maternal age, fetal loss rate after amniocentesis, report turn around time, and identification of other anomalies.

RESULTS

Overall, 87% (67,904/78,501) of women underwent screening. The rate of detection of trisomy 21 was 75% (80/107; 95% CI 66 to 83) with a 5.1% false positive rate (3466/67,904; CI 4.9 to 5.3%). In women under 30 years of age the detection rate was 60% (18/30; CI 41 to 77) with a 2.6% false positive rate (956/36,371; CI 2.5 to 2.8). The rate of detection of trisomy 18 was 57% (8/14; CI 29 to 82) with a 0.7% false positive rate (475/67,904; CI 0.64 to 0.76). Uptake of amniocentesis was 83% (2912/3508). Women were 3.3 times more likely to refuse amniocentesis if the risk was close to the cutoff (1 in 250) than if the risk was > or =1 in 50. Fetal loss within 28 days of amniocentesis was 0.9% (25/2912). Prenatal screening identified 84 other anomalies in addition to 41 cases of impending fetal death.

CONCLUSION

Second trimester prenatal screening for trisomy 21 and trisomy 18 using a simple two marker approach incorporating free beta hCG can achieve high detection rates over a long period of time. Health authorities who still have not introduced trisomy 21 screening should be encouraged by what can be achieved and should consider making such screening available to all women. Established second trimester detection rates of 75% for a 5% false positive rate will be the benchmark by which first trimester screening using nuchal translucency, PAPP-A and free beta hCG will be judged.

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.

A retrospective evaluation of second-trimester serum screening for fetal trisomy 18: experience of two laboratories

A retrospective study on screening methods for fetal trisomy 18 has been carried out in two different laboratories using the serum parameters: total human chorionic gonadotropin (hCG), unconjugated oestriol (uE3), and alpha-fetoprotein (AFP) in different combinations and in single marker protocols. Laboratory A (L(A)) utilized a radio-immunoassay to examine 38 fetal trisomy 18 cases and laboratory B (L(B)) utilized an enzyme-immunoassay to examine 33 trisomy 18 cases. As unaffected references the whole routine cohorts of each laboratory were used (L(A): 29 043; L(B): 4264). In both trisomy 18 study groups the median hCG and uE3 multiples of the median (MoM) values were markedly declined (L(A): 0.21 MoM, 0.37 MoM; L(B): 0.31 MoM, 0.44 MoM). Even after exclusion of trisomy 18 cases with combined neural tube or ventral wall defects the medians of AFP MoM values were only moderately declined (L(A): 0.73 MoM; L(B): 0.8 MoM). Receiver-operator characteristic (ROC) curves after multivariate discriminance analysis and single marker evaluation demonstrated that the difference of efficiency between a combination of hCG, uE3 and AFP, and a combination of hCG and uE3 is small but that any of these combinations are more efficient than a combination of hCG and AFP or single marker protocols, respectively. At a risk cut-off generating a false-positive rate of one per cent the most effective marker combination detected 31 of 38 (81.6 per cent) affected pregnancies in L(A) and 25 of 33 (75.8 per cent) in L(B). The differences in sensitivity and specificity seem to be due to the different analytical systems being utilized by the two laboratories.

Second-trimester maternal urine human chorionic gonadotrophin beta-core fragment concentrations in Asian pregnancies with fetal chromosomal abnormalities

The aim of this study was to investigate the second trimester concentrations of maternal urine human chorionic gonadotrophin beta-core fragment (HCGbetacf) in Asian pregnanci2es with fetal chromosomal abnormalities. HCGbetacf concentrations were analysed from 34 urine samples in chromosomally abnormal pregnancies, including 28 cases of Down's syndrome, one case of trisomy 18, and five cases of other chromosomal abnormalities (one mosaic deletion and four translocations), and in a cohort of 268 normal pregnancies receiving second trimester amniocentesis. Results were normalized to urine creatinine (Cr) concentration and converted to the multiple of the median (MOM) concentration for the appropriate gestation. The median HCGbetacf MOM concentrations of Down's syndrome pregnancies (12.89) was significantly higher than that of normal pregnancies (1. 06) (P < 0.00001). Wide variations of HCGbetacf concentrations were observed in other chromosomally abnormal pregnancies. There were 18 of 28 (64%) Down's syndrome cases but one of five (20%) other chromosomally abnormal cases with HCGbetacf concentrations above the 95th centile of the control values (8.22 MOM cut-off). These findings suggest that HCGbetacf could be a potential marker in urine screening for fetal Down's syndrome in Asians.

Clustering of trisomy 18 in Kuwait: Genetic predisposition or environmental?

BACKGROUND

This study describes 59 newborns with regular trisomy 18 (EdwardsA centAA syndrome, T18) who were ascertained clinically and cytogenetically at the Kuwait Medical Genetic Centre from 1994 to 1997, out of 118 T18 cases identified from 1980 to 1997.

MATERIALS AND METHODS

T18 cases were ascertained clinically and cytogenetically shortly after birth. In addition to assessing the T18 birth prevalence rate and confidence limits during the years 1994-1997, we investigated the possible etiological factors by a case-control study with normal healthy newborns. Studied factors included gender, parental age, birth order, abortion, clinical variables (presentation, amniotic fluid and mode of delivery), and survival.

RESULTS

The average T18 birth prevalence rate during the period was 8.95 per 10,000 live births (95% confidence limits 6.66-11.23). The T18 cases were mostly females, with a male:female ratio of 1:2.1, and the majority (53%) died before the second week of life. Maternal age above 30 years was found to be a significant factor for T18.

CONCLUSION

This high T18 birth prevalence rate suggests clustering of T18 in the highly inbred population of Kuwait. Such clustering may indicate a possible environmental, and to a lesser extent, genetic predisposition to aneuploidy nondisjunction.

Atypicality or specific screen: which is better at detecting non-Down's chromosomal anomalies?

I evaluated the value of adding a trisomy 18 screen to routine Down's screening and compared it with the benefits of atypicality screening. I studied 5080 unaffected pregnancies, 144 Down's syndrome and 190 non-Down's syndrome chromosome abnormalities (20 trisomy 13; 79 trisomy 18; 20 Turner's syndrome; 29 other sex chromosome abnormalities; 8 triploidy; and 34 miscellaneous). Using a one in 250 cut off, the Down's screen gave a screen positive rate of 4.07%; addition of atypicality without a trisomy 18 screen gave an extra 0.9% screen positives; trisomy 18 screening without atypicality gave an extra 0.51% screen positives; and atypicality screening after trisomy 18 screening gave 0.52% screen positives. Total screen positive rates were: Down's screening only, 4.07%; Down's screening + atypicality, 4.97%; Down's screening + trisomy 18 screen, 4.58%; Down's screening + trisomy 18 screen + atypicality, 5.09%. The detection rate for Down's syndrome using a one in 250 cut off was 58.9% and with addition of trisomy 18 and atypicality screening this increased to 59.3%, indicating that the extra screens add little to detection of Down's syndrome. For the other chromosomal abnormalities, Down's screening alone detected 22.6% of cases overall and addition of trisomy 18 and atypicality screening increased this to 49%. Examination of the marginal benefits of the extra screening tests revealed that the trisomy 18 screen was better at detecting chromosomal abnormalities than the Down's screen and that it would, therefore, be worthwhile adding this to all screening programs. Atypicality proved to be much less effective and it is suggested that this screen should only be applied in the early days of a screening program until sufficient data is available to design specific screens.

First-trimester urine free beta hCG, beta core, and total oestriol in pregnancies affected by Down's syndrome: implications for first-trimester screening with nuchal translucency and serum free beta hCG

We have examined maternal urine concentrations of beta core, free beta human chorionic gonadotrophin (hCG), and total oestriol in 373 control pregnancies and 43 pregnancies affected by aneuploidy (including 22 cases of Down's syndrome) in an attempt to see if any of the analytes have a value in Down's syndrome screening between the tenth and 14th week of pregnancy. We have compared the performance of these analytes against nuchal translucency measurement combined with maternal serum free beta hCG at the same period of pregnancy. Our results show that levels of urine free beta hCG and beta core are increased in Down's syndrome with average multiple of the median levels of 1.81 and 2.91, respectively. Urine total oestriol was reduced (0.83) whilst maternal serum free beta hCG was increased (1.72). In trisomy 18 the levels of all analytes were reduced, although serum free beta hCG was the most discriminating. The spread of results in the control and the Down's group for urine beta core was more than three times than that for serum free beta hCG and with urine free beta hCG it was two times wider. In combination with maternal age, urine total oestriol had a 32 per cent detection rate at a fixed 5 per cent false-positive rate; urine beta core 34 per cent, urine free beta hCG 36 per cent, maternal serum free beta hCG 44 per cent, and nuchal translucency 82 per cent. In combination with nuchal translucency, urine total oestriol added an extra 1 per cent detection, urine beta core an extra 2 per cent, urine free beta hCG an extra 3 per cent, and serum free beta hCG an extra 5 per cent. It is unlikely that any of the urine markers will be of value in first-trimester screening. Optimal first-trimester screening programmes will rely for the foreseeable future on nuchal translucency, serum free beta hCG, and possibly pregnancy-associated plasma protein A.

Atypicality revisited: further data on the effectiveness of the Mahalanobis distance in Down's syndrome screening

Further data suggesting that assessment of atypicality may be a valuable addition to Down's syndrome screening is presented, based on results from 1521 unaffected pregnancies and 190 chromosomally abnormal pregnancies. For a 1% increase in false positive rates (over the Down's screening-related false positives), it is estimated that the detection of non-trisomy 21 abnormalities may be enhanced by approximately 40%. These false positive and detection rates are similar to previous reports for specific trisomy 18 screens. Further work is necessary to prove whether a specific trisomy 18 screen, or an atypicality screen is preferable.

Counselling implications of chromosomal abnormalities other than trisomy 21 detected through a maternal serum screening programme

OBJECTIVE

To identify counselling requirements, we reviewed the frequency and type of non-trisomy 21 chromosome abnormalities found at amniocentesis after maternal serum screening for Down's syndrome.

DESIGN

The study involved a review of the cytogenetic results of amniocenteses performed because of a raised maternal serum screening risk.

SETTING

The maternal serum screening and amniocenteses were performed at hospitals in the Yorkshire region.

SAMPLE

1715 amniocenteses were performed as a result of a raised maternal serum screening risk for the period 1990 to 1993.

METHODS

The cytogenetic results were classified into the main categories of numerical and structural chromosomal abnormalities.

MAIN OUTCOME MEASURES

The nature and frequency of abnormal cytogenetic results were identified in which parental samples were required in order to determine if the abnormal finding was de novo or familial and/or for which specialist genetic counselling was required.

RESULTS

Sixty-nine pregnancies of 1715 amniocenteses were identified with a chromosomal abnormality (4.0%): 35 (2.0%) with trisomy 21 and 34 (2.0%) with another chromosomal abnormality. For 20 of these 34 abnormalities, parental karyotypes were required and in 29 of the 34 specialist genetic counselling was required.

CONCLUSIONS

Women undergoing maternal serum screening and, in particular, those proceeding to amniocentesis, should be informed that there is an equal chance that a chromosomal abnormality other than trisomy 21 will be found at amniocentesis, the nature of which usually requires parental samples and specialist counselling.

Urine free beta hCG and beta core in pregnancies affected by Down's syndrome

Urine beta core was shown in recent studies to be markedly elevated in pregnancies affected by Down's syndrome in the late second trimester. Free beta human chorionic gonadotropin (hCG) has also been shown to be the most discriminatory maternal serum marker of Down's syndrome. Since free beta hCG is rapidly cleared from the maternal circulation, we have carried out a study to evaluate whether free beta hCG is elevated in the urine of pregnancies affected by Down's syndrome and to investigate whether urine beta core or urine free beta hCG may be used as possible screening markers. Urine samples from 29 cases of Down's syndrome, three cases of trisomy 18, and 400 control pregnancies were analysed for the two prospective markers. Results were corrected for urine concentration by expressing marker concentrations at a fixed creatinine concentration and then expressing the results as multiples of the median for unaffected pregnancies of the same gestation. The median value of beta core in the Down's syndrome pregnancies was 2.35 compared with 2.47 for free beta hCG. Free beta hCG distributions were closely similar to those in maternal serum. Using free beta hCG, we predict Down's syndrome detection rates of 58 per cent at a 5 per cent false-positive rate. Using beta core, however, this rate fell to 41 per cent. Measurement of free beta hCG in urine may present a feasible route for screening pregnant populations, particularly where community-based obstetric care is the norm and/or if early first-trimester screening becomes a reality.

Dimeric inhibin A as a marker for Down's syndrome in early pregnancy

BACKGROUND

In screening for Down's syndrome in the second trimester of pregnancy, the concentrations of alpha-fetoprotein, the beta subunit of human chorionic gonadotropin, and intact human chorionic gonadotropin in material serum are widely used markers. We investigated a new marker, dimeric inhibin A, and compared its predictive value with that of the established markers.

METHODS

Serum samples were obtained at 7 to 18 weeks of gestation from 58 women whose fetuses were known to be affected by Down's syndrome, 32 whose fetuses were affected by trisomy 18, and 438 whose fetuses were normal, and the samples were analyzed for each marker. Individual serum concentrations of each marker were converted to multiples of the median value at the appropriate length of gestation in the women with normal pregnancies, and rates of detection of Down's syndrome by screening for inhibin A in various combinations with the other markers were estimated by multivariate analysis.

RESULTS

In the women with fetuses affected by Down's syndrome, the serum inhibin A concentrations were 2.06 times the median value in the women with normal pregnancies (P < 0.001). This compared with 2.00 times the median for the beta subunit of human chorionic gonadotropin, 1.82 times the median for intact human chorionic gonadotropin, and 0.72 for alpha-fetoprotein. The serum concentrations of inhibin A in the women with fetuses affected by Down's syndrome did not appear to be significantly elevated above normal until the end of the first trimester and were not significantly different from normal in the women with fetuses affected by trisomy 18 (P = 0.17). The rate of detection of Down's syndrome was 53 percent and the false positive rate was 5 percent when alpha-fetoprotein, the beta subunit of human chorionic gonadotropin, the maternal age were used together as predictors. The detection rate increased to 75 percent when inhibin A was added (P = 0.002).

CONCLUSIONS

In the second trimester of pregnancy, measuring inhibin A in maternal serum, in combination with measurements of alpha-fetoprotein and beta subunit of human chorionic gonadotropin, significantly improved the rate of detection of Down's syndrome.

The usefulness of hCG and unconjugated oestriol in prenatal diagnosis of trisomy 18

OBJECTIVE

To evaluate the usefulness of the two maternal serum markers, human chorionic gonadotrophin (hCG) and unconjugated oestriol (uE3), in the prenatal diagnosis of trisomy 18.

DESIGN

Retrospective evaluation of uE3 and hCG levels at mid-trimester in cases ot trisomy 18 pregnancies identified from a series of women screened for Down's syndrome.

SETTING

From a series of 53,893 women screened in the antenatal centre of University Hospital of Caen (France), 22 cases of trisomy 18 were diagnosed either after amniocentesis for maternal age, elevated risk of Down's syndrome, or fetal abnormalities and/or growth retardation on ultrasound assessment, or after birth. In addition, ll cases of trisomy 18 identified prenatally in two other centres were included.

RESULTS

Individual hCG and uE3 levels for pregnancies with trisomy 18 were significantly lower than in unaffected pregnancies: mean hCG was 0.62 multiples of the median (MoM) and median hCG was 0.5 MoM. uE3 was a much more effective marker than hCG. Mean uE3 was 0.40 MoM and median uE3 was 0.37 MoM. It was observed that screening for trisomy 18 based on selection for amniocentesis with cut-off values of 0.55 for hCG and 0.60 for uE3 would lead to a detection rate of 48% for 0.8% false positive rate. Using cut-off values of 0.70 MoM for each one of the two markers would detect 79% of cases of trisomy 18 with 3% false positive rate.

CONCLUSIONS

Our results confirm that low hCG and uE3 levels observed in the mid-trimester are predictive of an increased risk for trisomy 18. Since most fetuses with trisomy 18 exhibit morphological abnormalities which should be detected following a careful ultrasonographic examination, biochemical screening could help in the detection of those anatomical defects in selecting for scanning a group of high risk women.

Risk-based prenatal screening for trisomy 18 using alpha-fetoprotein, unconjugated oestriol and human chorionic gonadotropin

Nine centres collaborated to examine the feasibility of a screening method for trisomy 18 that was based on assigning individual risk, using a combination of maternal age and measurements of alpha-fetoprotein (AFP), unconjugated oestriol (uE3), and human chorionic gonadotropin (hCG). Second-trimester measurements of these analytes were obtained from 94 trisomy 18 pregnancies. In the 89 pregnancies without an associated open defect, the median levels for AFP, uE3, and hCG were 0.65, 0.43 and 0.36 multiples of the unaffected population median, respectively. The strongest individual predictor of risk for trisomy 18 was uE3, followed by hCG, AFP, and maternal age, in that order. Using a method of individual risk estimation that is based on the three markers and maternal age, 60 per cent of pregnancies associated with trisomy 18 would be detected at a risk cut-off level of 1:100, with a false-positive rate of about 0.2 per cent. One in nine pregnancies identified as being at increased risk for trisomy 18 would be expected to have an affected pregnancy. This risk-based screening method is more efficient than an existing method that is based on fixed analyte cut-off levels. Even though the birth prevalence of trisomy 18 is low, prenatal screening can be justified when performed in conjunction with Down syndrome screening and when a high proportion of women offered amniocentesis have an affected fetus.