Expanding multiple marker screening for Down's syndrome to include Edward'S syndrome

Information on maternal age and maternal serum alpha-fetoprotein, unconjugated oestriol (uE₃), and human chorionic gonadotrophin (hCG) levels was used to investigate retrospectively the effect of estimating Edward's syndrome risk in women having multi-marker screening for Down's syndrome. The screened population comprised 15 pregnancies affected by Edward's syndrome, 15 with Down's syndrome and 5472 unaffected pregnancies. The use of all three markers to estimate Edward's syndrome risk would have led to the detection of 10–12 (67–80 per cent) cases with a false-positive rate of 0.3–0.6 per cent depending on the risk cut-off. A further case would have been detected as a result of screening for Down's syndrome alone. Similar results were obtained when the Edward's syndrome risk was based on uE₃ and hCG only. These data suggest that extending Down's syndrome screening to include Edward's syndrome risk will yield a high detection rate with only a small increase in the false-positive rate.     

Urinary β-core human chorionic gonadotrophin: A new approach to Down's syndrome screening

Human chorionic gonadotrophin (hCG) is the most discriminatory maternal serum marker of Down's syndrome. We have carried out a study to establish whether urinary β-core-hCG, a major metabolic product of hCG, might be an even better marker. Urine samples were available from seven singleton pregnancies with Down's syndrome, and one each of Edwards' syndrome, triploidy, and twins discordant for Down's syndrome. β-Core-hCG levels were corrected for creatinine and expressed as multiples of the normal gestation-specific median (MOM) level derived from 67 singleton controls. There was a highly statistically significant elevation in level among the singleton Down's syndrome cases (P<0·0005; Wilcoxon rank sum test). All had levels exceeding 2 MOM with a median of 6·11 MOM (95 per cent confidence interval 3·7–10·0). The levels were extremely low in Edwards' syndrome (0·08 MOM) and triploidy (0·02 MOM), but the twin pregnancy discordant for Down's syndrome did not have a raised β-core-hCG level (0·64 MOM). The findings are sufficiently encouraging to investigate the possibility of urinalysis as a routine modality in the prenatal screening for Down's syndrome and other common serious aneuploidies.     

Urinary multiple marker screening for down's syndrome

We have examined the possibility of using multiple markers in maternal urine rather than serum in order to screen for Down's syndrome. Urine samples were available from 36 cases (24 Down's syndrome, five Edwards' syndrome, three Turner's syndrome, one Klinefelter's syndrome, one triploidy, one triple-X, one twin discordant for Down's syndrome) and 294 controls, including three twins. Three markers were tested: the β-core fragment of human chorionic gonadotrophin (hCG), total oestrogen (tE) and the free a subunit of hCG. Levels were corrected for creatinine excretion and expressed as multiples of the gestation-specific median (MOM) level from the singleton controls. The median value for the singleton Down's syndrome cases was 6.02, 0.74, and 1.08 MOM for β-core-hCG, tE, and a-hCG, respectively. The increases in β-core-hCG and the reduction in tE levels were highly significant (P<0.0001 and 0.005, respectively; Wilcoxon rank sum test) but the increase in free a-hCG was not (P=0.40). On the basis of a mathematical model, the expected detection rate for a 5 per cent false-positive rate was 79.6 per cent for β-core-hCG alone, which increased to 82.3 per cent when combined with tE. Aneuploidies other than Down's syndrome were characterized by low levels of tE and either low or high β-core-hCG.     

Second-trimester cancer antigen 125 and Down's syndrome

This study explores if assay of cancer antigen 125 (CA 125) in maternal serum might aid the detection of Down's syndrome in the second trimester of pregnancy. CA 125 levels were determined retrospectively in stored maternal serum samples from ten Down's syndrome pregnancies and 78 controls matched for gestational and maternal age. In addition, second-trimester amniotic fluid samples from nine Down's syndrome and 109 unaffected pregnancies were analysed for CA 125. Maternal serum CA 125 values for Down's syndrome pregnancies were lower, with the median being 0.72 multiples of the unaffected population median. The medians for affected and unaffected pregnancies did not differ significantly and there was a considerable overlap in the range of values of cases and controls. The distribution of amniotic fluid CA 125 levels for Down's syndrome pregnancies resembled that for controls. From our present results, we could not find an association between Down's syndrome and second-trimester maternal serum or amniotic fluid CA 125 levels.     

CA-125 as a maternal serum marker for Down's syndrome in the first and second trimesters

CA-125, alpha-fetoprotein (AFP), and human chorionic gonadotropin (HCG) were determined in maternal serum in the first trimester from 14 women with a Down's syndrome fetus and 61 women with a healthy fetus. In the second trimester, 15 and 60 serum samples were determined from women with a Down's syndrome and a healthy fetus respectively. In both trimesters, maternal serum CA-125 was found to be elevated in Down's syndrome pregnancies compared with controls. Using discrimination functions, our preliminary results indicate that CA-125 is a better marker than AFP and HCG respectively for a Down's syndrome fetus in the first trimester and improves the detection rate in the second trimester.     

Second-trimester maternal serum immunoreactive inhibin as a marker for fetal Down's syndrome

We measured immunoreactive inhibin in the maternal serum of 80 pregnancies with a chromosomally normal fetus and ten Down's syndrome pregnancies in the second trimester. The inhibin level in all Down's syndrome pregnancies was above the normal median; the multiple of the normal median (MoM) was 1.9. We found a statistically significant difference between the levels of inhibin in unaffected and affected pregnancies (Kolmogorov–Smirnov test: p <0.002). Using an arbitrarily chosen cut-off of 2.4 MoM, 40 per cent of Down's syndrome and 5 per cent of the normal pregnancies were found. We conclude that immunoreactive inhibin may be useful as a marker for fetal Down's syndrome.     

Prenatal screening for chromosome abnormalities using maternal serum chorionic gonadotrophin,alpha-fetoprotein,and age

Human chorionic gonadotrophin (hCG) levels were assayed retrospectively in stored maternal serum samples from 78 chromosomally abnormal pregnancies and 410 controls matched for gestation and maternal age. The median serum hCG concentration in 49 pregnancies with Down's syndrome was significantly elevated, at 2.18 multiples of the normal median. Significantly reduced hCG concentrations were found in a group of four trisomy 18 pregnancies (all less than 0.4 multiples of the median). Eight cases of unbalanced chromosome rearrangements appeared to show some lowering of hCG levels, while there was no significant difference in the levels in the cases of trisomy 13, balanced translocations, and sex chromosome abnormalities. Maternal serum hCG alone is a better indicator of Down's syndrome pregnancies than maternal age or maternal serum alpha-fetoprotein (AFP), either individually or in combination, and provides a further virtually independent measure of risk. On the basis of our findings, screening for Down's syndrome using hCG and AFP results combined with maternal age risks is predicted to result in a higher detection rate (57 per cent) for a lower false-positive rate (5.0 per cent) than would be attainable by combined AFP and age screening (37 per cent detection at a 6.6 per cent false-positive rate).     

45,X karyotype: May the diagnosis be suspected on ultrasonic examination in the second trimester of pregnancy?

We report three cases of Turner's syndrome with cystic hygromata, which were diagnosed by routine ultrasound scanning before amniocentesis in the second trimester of pregnancy. Maternal and amniotic level of alpha-fetoprotein were normal. Karyotyping carried out afterwards showed a 45,X karyotype. Our data indicate, that cystic hygromata in Turner's syndrome may coexist with a normal amniotic fluid AFP, thus questioning the theory of leakage from the hygroma. It remains to be investigated if all cases of Turner's syndrome present a cystic hygroma in utero.     

Second-trimester maternal serum screening using alpha-fetoprotein,human chorionic gonadotrophin,and unconjugated oestriol: Experience of a regional programme

Over a 2-year period from January 1991 to December 1992, second-trimester maternal serum screening for Down's syndrome using alpha-fetoprotein (aFP), human chorionic gonadotrophin (hCG), and unconjugated oestriol (uE₃) was made available to five health districts in East Anglia, with a total population of 1·2 million. Amniocentesis was offered when the risk of Down's syndrome at term was 1:200 or greater. 25359 singleton pregnancies were screened, representing an uptake of 77 per cent. The recall rate for the 24 per cent of women who had not had a dating scan prior to the test was 9·4 per cent compared with 3·9 per cent for those who had been scanned (P<0·0005). Seventy-five per cent (36/48) of Down's syndrome pregnancies were detected for a false-positive rate of 4·0 per cent. Twenty-five out of 36 of detected Down's syndrome pregnancies were dated by scan prior to sampling, and in the 11 remaining cases, the dates were confirmed by scan after a high-risk result was obtained. The exclusion of uE₃ from the screening protocol would have reduced the detection rate to 52 per cent (25/48) for the same false-positive rate. Eighty-five per cent of women identified at high risk accepted the offer of an amniocentesis. Other fetal abnormalities detected were trisomy 18 (3), trisomy 13 (2), 45,X (6), 69,XXX (5), other chromosome abnormalities (9), open neural tube defects (26), hydrocephalus (7), abdominal wall defects (4), and steroid sulphatase deficiency (6).     

Maternal smoking habits and Down's syndrome

Two series of pregnancies were studied to investigate the relationship between maternal smoking and the risk of fetal Down' s syndrome. In the first series, ascertained in the 1960s, in which smoking habits were determined after the outcome of pregnancy was known, the proportion of smokers (47 per cent) among the 461 women whose pregnancies ended in the birth of an infant with Down' s syndrome was similar to that in the 461 controls (46 per cent) who had pregnancies affected by other congenital disorders. In the second series, ascertained between 1973 and 1984, smoking habits were determined by measurement of cotinine in antenatal serum samples that were routinely collected and stored or, if a serum sample was not available, from information in the antenatal notes. In this series, the proportion of smokers (14 per cent) among the 91 women who had pregnancies associated with Down' s syndrome was lower than that among 413 controls (19 per cent), though this was not statistically significant. Collectively, our results provide no evidence for an association between fetal Down' s syndrome and smoking. Other published studies found a deficit of smokers among women who had pregnancies associated with Down' s syndrome. This may be partly due to some studies not taking adequate account of maternal age (older women are more likely to have had a Down' s syndrome pregnancy but are less likely to be smokers) and partly due to the greater tendency for positive findings to be published than negative ones.     

Improved parameters for risk estimation in Down's syndrome screening

A new method is described for calculating maternal serum marker distribution parameters which will improve risk estimation when screening for Down's syndrome. The approach is to calculate parameters using data from the local screened population and data obtained by meta-analysis from all published studies. The local data are used to derive the variance and covariance in unaffected pregnancies. The meta-analysis is used for the mean level in Down's syndrome pregnancies together with the differences in variance and covariance between affected and unaffected pregnancies. Forty-four published studies were analysed. The mean level for Down's syndrome in multiples of the normal median was 0·73 for alpha-fetoprotein (AFP) in total of 1140 pregnancies, 0·73 for unconjugated oestriol (uE₃) in 613, 2·02 for human chorionic gonadotropin (hCG) in 850, and 2·30 for free β-hCG in 477. For all four markers, the variance in Down's syndrome was higher than in unaffected pregnancies; for AFP and uE₃, the covariances were also higher in Down's syndrome, but for the other markers they were lower. The method was illustrated using data from 6387 pregnancies screened in Leeds.     

Economic assessment of maternal serum screening for Down's syndrome using human chorionic gonadotropin

The effectiveness and costs of prenatal screening programmes for Down's syndrome using maternal serum markers will vary significantly depending on the biological cut-off values chosen in order to select women, at each maternal age, who will be sent for amniocentesis. On the basis of the first French prospective study of human chorionic gonadotropin (hCG) measurement in maternal serum, this paper shows that the screening protocol currently used in France, where hCG cut-off values are defined in order to offer amniocentesis to women of all ages with a 1 percent fetal risk of Down's syndrome, would detect 64·06 per cent of all cases of trisomy 21 at birth and would be highly profitable for the French social security system. On the basis of a representative sample of 100 000 pregnant women, the total costs of screening would reach $8 302 000 but would generate net potential savings of $32 186 000 in terms of life-long costs of care for trisomic 21 children which would be ‘avoided’ by termination of pregnancy following a positive diagnosis of Down's syndrome. Economic assessment shows that cost-benefit analysis would justify lower hCG cut-off values and a higher detection rate of fetal Down's syndrome (74·45 per cent) than the current French protocol. This paper concludes that it is ethical and value-laden issues, such as the consequences for women and couples of false positives and false negatives of screening, rather than economic and financial arguments that may set limits to the utilization of screening for Down's syndrome using maternal serum markers like hCG.     

First-trimester maternal serum human chorionic gonadotrophin as a marker for fetal chromosomal disorders

The Dutch Working Party on Prenatal Diagnosis has initiated a study on the possibilities of first-trimester screening for fetal chromosomal disorders. We report on maternal serum human chorionic gonadotrophin (MS-hCG) measurements in 1348 pregnancies with a chromosomally normal fetus and 53 pregnancies with a chromosomally abnormal fetus. The median MS-hCG concentration in 24 pregnancies with Down's syndrome was 1.19 multiples of the normal median (MoM). The MS-hCG distributions in normal and Down's syndrome pregnancies did not differ significantly (t-test: t = 1.945, p >0.05). We also found no difference between normal pregnancies and pregnancies with other chromosomal disorders (six cases of trisomy 18, MoM = 0.80; four cases of sex chromosome abnormality, MoM = 1.01; 17 cases of chromosomal mosaicism in chorionic villi, MoM = 1.11). Selecting an upper limit at the 90th centile could detect 25 per cent of pregnancies with Down's syndrome. We conclude that, in the first trimester, MS-hCG as a screening factor for Down's syndrome is of minor value. However, MS-hCG could be a useful factor in a first-trimester screening programme based on a combination of markers.     

Cytogenetic prenatal diagnosis and its relative effectiveness in the mersey region and North Wales

The relative effectiveness of cytogenetic prenatal diagnosis in the Mersey Region and North Wales is presented by estimating the percentage detection rates of Down's syndrome annually following amniocentesis from 1978–1984 inclusive. Tables indicating the percentage of screened pregnancies, types of chromosomal aberrations detected and the occurrence of Down's syndrome in mothers in age groups of five-year intervals are also presented. The average prenatal detection rate for Down's syndrome (estimated at the time of birth) was 15–15 per cent over the years 1978–1984 and was above 22 per cent for the last two years when 44–13 per cent of all pregnancies to mothers of 35 years and over were investigated.     

First-trimester maternal serum alpha-fetoprotein as a marker for fetal chromosomal disorders

We evaluated first-trimester maternal serum alpha-fetoprotein (MS-AFP) as a marker for fetal chromosomal disorders. The multicentre study was performed under the auspices of the Dutch Working Party on Prenatal Diagnosis. MS-AFP was measured in 2404 normal pregnancies and 72 chromosomally abnormal pregnancies. The median multiple of the normal median (MOM) in 32 Down's syndrome pregnancies was 0·83 with a 95 per cent confidence interval ranging from 0·60 to 1·04. The difference between the distributions of first-trimester MS-AFP in normal and Down's syndrome pregnancies was statistically significant (t-test: t = 2·34, P<0·05). Thirty-one per cent of the Down's syndrome pregnancies were found below the tenth percentile. We found no difference between normal pregnancies and pregnancies with other chromosomal disorders (eight cases with trisomy 18, MOM = 1·26; seven cases with sex chromosome abnormalities, MOM = 1·07; 22 cases with a chromosomal mosaic pattern in chorionic villi, MOM = 1·08). We conclude that first-trimester MS-AFP can discriminate between normal and Down's syndrome pregnancies, but is not an effective marker. First-trimester MS-AFP has no value as a marker for other fetal chromosomal disorders.     

Evaluation of maternal serum dimeric inhibin a as a first-trimester marker of down's syndrome

While second-trimester prenatal screening programmes for Down's syndrome have become established in prenatal care, it would be advantageous to be able to offer screening in earlier preganancy. To this end, we have evaluated a new potential maternal serum marker, dimeric inhibin A, as a possible first-trimester marker. Dimeric inhibin A was measured in propsectively collected maternal serum from 23 cases of Down's syndrome and matched chromosomally normal controls, at 11–13 weeks' gestation. Levels of this protein were significantly elevated in the Down's pregnancies compared with the control pregnancies. The median multiple of the normal median (MOM) for the Down's samples was 2.46 (95 per cent confidence interval: 2.11–3.26, P<0.0001 vs. controls). These results suggest that dimeric inhibin A is a useful discriminator of Down's-affected pregnancies from normal pregnancies in the first trimester and that sensitive screening in combination with maternal age and other possible markers may be practicable in the first trimester.     

Improved performance in a prenatal screening programme for Down's syndrome incorporating serum-free hCG subunit analyses

A prenatal screening programme for Down's syndrome potentially detecting 76 per cent of affected pregnancies in the South Australian general population at an amniocentesis rate of 3.9 per cent was designed following analysis of mid-trimester serum samples from 57 women who carried an affected fetus. This equates to one affected pregnancy being detected for 41 chromosomal analyses performed. For the experimental series, 75.4 per cent of affected pregnancies were detected, while 4.1 per cent of control specimens produced estimated risk odds consistent with further action. A maternal risk odds of birth of a Down's syndrome fetus of 1:420 was taken as the decision value, which is the prevalence of Down's syndrome births to 35-year-old mothers in South Australia. This screening performance was achieved by investigating combinations of serum analytes not previously reported and by refining the calculation of maternal risk odds to include selective weighting of indicator analytes. Combination of the measurements of free α-subunits and β-subunits of chorionic gonadotrophin, α-fetoprotein, unconjugated oestriol, and placental lactogen was found to be most effective in indicating Down's syndrome fetuses. In all combinations of analytes tested, replacing the measurements of free α-subunits and free β-subunits of chorionic gonadotrophin with the measurement of intact chorionic gonadotropin produced a less effective screen.     

Birth prevalence of down's syndrome in England and Wales

The natural birth prevalence of Down's syndrome for England and Wales in 1974–1987 (i.e., the birth prevalence in the absence of prenatal diagnosis and the induced abortion of affected pregnancies) was estimated by applying the maternal age-specific birth prevalence derived from epidemiological studies to the number of births in single-year age groups tabulated by the Office of Population Censuses and Surveys (OPCS). On average, the natural birth prevalence was 12.6 per 10 000 births and increased slightly from 12.2 to 13.2 per 10 000 births over the 14-year period. Using data on induced abortions carried out on account of Down's syndrome reported to OPCS under the statutory abortion notification scheme, 14 per cent of affected births were avoided by the induced abortion of affected pregnancies, so that the actual birth prevalence of Down's syndrome was estimated at 10.8 per 10000 births. Using data on Down's syndrome births reported to OPCS under the voluntary congenital malformation notification scheme, the prevalence was 7.2 per 10000 births, so only 67 per cent of the estimated number of affected births were, in fact, notified to the scheme.     

First-trimester screening for fetal chromosomal abnormalities. Preliminary results

We have started a multicentre trial to study the possibilities of first-trimester maternal serum screening for fetal chromosomal abnormalities. Maternal blood samples were obtained before 13 weeks of gestation. We present the preliminary results of the first 950 patients on alpha-fetoprotein (AFP). Results on cancer antigen 125 (CA 125) in Down's syndrome and normal pregnancies are also presented. We conclude that the results on AFP are promising and that CA 125 might be predictive for fetal Down's syndrome.