Serum markers for Down's syndrome in women who have had in vitro fertilisation: implications for antenatal screening

To examine the Down's syndrome screening positive rate among in vitro fertilisation (IVF) pregnancies, we measured second trimester serum marker levels in singleton IVF pregnancies (cases) and in five non–IVF pregnancies (controls) matched to each case for gestational age, age of mother, and duration of storage of the serum sample. There were 151 IVF pregnancies in which alpha fetoprotein, unconjugated oestriol (uE₃), free β–human chorionic gonadotrophin (hCG) and total hCG were measured, 104 IVF pregnancies in which free α-hCG was measured, and 39 IVF pregnancies in which inhibin A was measured. Median uE₃ levels were 6% lower (   P = 0.003  ), median free β–hCG 9% higher (   P = 0.024  ), and median total hCG 14% higher (   P = 0.026  ) in IVF pregnancies compared with controls. The screen positive rate in the IVF pregnancies (28%) was about twice as high as that in controls (17%). High hCG levels may be explained by progesterone remaining high in IVF pregnancies. The low uE₃ levels remain unexplained. In Down's syndrome screening in IVF pregnancies hCG and uE₃ values should be adjusted to avoid the high screen positive rate.     

Detection of hydatidiform mole in maternal serum screening programmes for Down's syndrome.

OBJECTIVE: To determine how frequently hydatidiform mole will be detected in a maternal serum Down's syndrome screening programme. DESIGN: Affected pregnancies were identified using a national register. Unconjugated oestriol (uE3) and human chorionic gonadotrophin (hCG) were measured in stored serum samples and alphafetoprotein (AFP) levels were available from previous neural tube defect screening at 15-20 weeks gestation. SUBJECTS: Ten pregnancies with a complete mole (i.e., hydropic placenta without a fetus), nine with stored serum samples and one with an AFP level only. RESULTS: The median values were 0.08, 0.13 and 1.83 multiples of the normal median for AFP, uE3 and hCG respectively. Six out of nine (67%) tested for all three markers had a high risk of Down's syndrome given maternal age and the marker levels. CONCLUSION: Many molar pregnancies that have not presented clinically before 15 weeks will be detected through Down's syndrome screening.     

Maternal serum unconjugated oestriol and human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down's syndrome.

OBJECTIVE--To investigate maternal serum unconjugated oestriol (uE3) and human chorionic gonadotrophin (hCG) levels in twin pregnancies and to consider the implications of the results for antenatal screening for Down's syndrome. DESIGN--Measurement of maternal serum uE3 and hCG levels from 15-22 weeks of gestation in twin and singleton pregnancies. Previously available maternal serum alpha-fetoprotein (AFP) levels were also presented. SETTING--Stored serum samples collected from women receiving routine antenatal care in Oxford were used. SUBJECTS--200 women with a twin pregnancy and, for each, three singleton control pregnancies matched for gestational age (same completed week of pregnancy) and duration of storage of the serum sample (same calendar quarter). RESULTS--The median uE3, hCG and AFP levels in the twin pregnancies were respectively, 1.67 (95% CI 1.56-1.79), 1.84 (95% CI 1.64-2.07) and 2.13 (95% CI 1.97-2.31) multiples of the median (MoM) for singleton pregnancies at the same gestational age. The variance of values for the three serum markers (expressed in logarithms), and the correlation coefficients between any two, were similar in the twin and singleton pregnancies. CONCLUSION--In maternal serum screening programmes for Down's syndrome dividing uE3, hCG and AFP MoM values in twin pregnancies by the corresponding medians for twin pregnancies will, in expectation, yield a similar false-positive rate in twin pregnancies as in singleton pregnancies.     

Second trimester amniotic fluid oestriol, dehydroepiandrosterone sulphate, and human chorionic gonadotrophin levels in Down's syndrome.

OBJECTIVE--To investigate the reason for low maternal serum unconjugated oestriol (uE3) and raised human chorionic gonadotrophin (hCG) levels in Down's syndrome pregnancies. DESIGN--Measurement of uE3, total oestriol (tE3), dehydroepiandrosterone sulphate (DHEAS), a precursor of oestriol, and hCG in 15-20 week amniotic fluid samples from pregnancies with and without Down's syndrome. SETTING--The retrieval and use of stored amniotic fluid samples collected from women who had had an amniocentesis for antenatal diagnosis. SUBJECTS--45 women with a Down's syndrome pregnancy and 224 unaffected controls of the same gestational age. RESULTS--The median level of amniotic fluid in affected pregnancies was low for uE3, tE3 and DHEAS but high for hCG: 0.50, 0.46, 0.35 and 1.58 multiples of the normal median, respectively. CONCLUSION--These results suggest that the abnormal maternal serum levels of uE3 and hCG in affected pregnancies are due mainly to abnormal feto-placental synthesis, rather than feto-maternal transfer.     

Second-trimester maternal serum screening for Down syndrome in in vitro fertilization pregnancies

OBJECTIVES: To examine whether second-trimester maternal serum triple marker screening results differ between in vitro fertilization (IVF) pregnancies and naturally conceived pregnancies. METHODS: Second-trimester maternal serum triple marker screening results from 88 IVF pregnancies were compared with 596 naturally conceived pregnancies (controls). Controls were matched to each IVF pregnancy by maternal age, gestational age and date of blood collection. All pregnancies in the study were known to have normal outcome. Multiple of the median (MoM) levels of human chorionic gonadotrophin (hCG), unconjugated estriol (uE3) and alpha-fetoprotein (AFP), and the false-positive rate for Down syndrome were compared between the two groups. RESULTS: No statistically significant differences in analyte levels or in Down syndrome false-positive rate were observed between the IVF and naturally conceived pregnancies. CONCLUSION: IVF patients can be counselled about maternal serum triple marker screening in the same manner as patients with naturally conceived pregnancies. There is no evidence to support the general use of analyte correction factors in the interpretation of second-trimester maternal serum screen results in IVF pregnancies.     

Second-trimester double or triple screening for Down syndrome: a comparison of Chinese and Caucasian populations.

OBJECTIVES: To compare the performance of double screening (measuring maternal serum levels of alpha-fetoprotein [AFP] and total beta-human chorionic gonadotrophin [hCG] as markers for Down syndrome) with that of triple screening (also measuring levels of unconjugated estriol [uE3]) in the second trimester of pregnancy, and to compare ethnic variance between Chinese and Caucasian populations. METHODS: The study investigated 15096 normal singleton pregnancies and 24 pregnancies affected with Down syndrome. Frequency distributions of AFP, hCG, and uE3 levels were analyzed. Likelihood ratios (LRs) were calculated using the multiple of median value (MoM) of AFP, hCG, and uE3 as variables. After multiplying maternal age risk by the LR values for the markers used in double and triple screening, the specific risks obtained with double and triple screening were estimated. The detection rate (DR) and false-positive rate (FPR) were calculated at different cut-off points. The serum markers' levels were also compared with those of Caucasian women. RESULTS: The median MoM value of hCG was higher in women with affected pregnancies (1.40) than those with unaffected pregnancies (1.00). However, the median MoMs of AFP and uE3 (0.79 and 0.68) were lower in affected than in unaffected pregnancies. At a FPR of 5%, the detection rates reached with double and triple screening were 50% and 66.7%, respectively. Ratios of the 3 serum markers' medians to those in a study with Caucasian women were 1.06 (range=1.04-1.09) for AFP, 1.14 (range=1.10-1.17) for hCG, and 1.28 (range=1.23-1.41) for uE3 for the relevant gestational weeks. CONCLUSION: Triple screening performed better than double screening in the second trimester. Ethnic variance should be taken into account in Down syndrome screening.     

The best marker combination using the integrated screening test approach for detecting various chromosomal aneuploidies

AIMS: To evaluate the cross-trimester multiple marker correlation and the minimum marker combination needed for detecting various chromosomal aneuploidies. MATERIALS AND METHODS: Parturient women with singleton pregnancies who underwent non-interventional sequential screening test and followed prospectively were recruited. They all underwent first trimester combined nuchal translucency (NT), pregnancy-associated plasma protein-A (PAPP-A), and free beta-human chorionic gonadotrophin (f-betahCG), followed by second trimester measurement of unconjugated estriol (uE3), human chorionic gonadotrophin (hCG) and alpha-fetoprotein (AFP). Pearson correlation was applied to compute any cross-trimester marker correlation and logistic regression analysis was used to determine the minimum marker combination for detecting various categories of chromosomal aneuploidies. RESULTS: The current study included 552 normal and 43 chromosomal-affected pregnancies (24 Down's syndrome [DS], 7 Turner's syndrome, 8 Edward's syndrome, 4 Klinefelter syndrome and 5 triploidy) for which the results of both the screening tests and the pregnancy outcome were available. In the normal cases, a significant correlation was found between f-betahCG and hCG (r=0.52), as well as between PAPP-A and uE3 (r=0.174). In DS pregnancies, the NT correlated with both hCG (r=0.45) and uE3 (r=-0.39). In Turner's syndrome, uE3 correlated both with PAPP-A (r=0.97) and f-betahCG (r=0.97). No other significant correlations were found. Furthermore, with the exception of f-betahCG and hCG in the unaffected cases, all other markers correlation appeared very weak. For detecting all the above categories of aneuploidies, the combination of NT, PAPP-A and uE3 and the maternal age background risk were found adequate, with a 74% detection rate (DR) for a 5% false positive rate (FPR). For DS only, the combination of maternal age-related background risk and the combination of NT, PAPP-A, hCG and AFP yielded a 79% DR for a 5% FPR. CONCLUSIONS: The current study agrees with a previous report that, overall, there is no strong correlation between first and second trimester markers. The extension of the integrated test for detecting various categories of common chromosomal aneuploidies using NT, PAPP-A and uE3 deserves further evaluation.     

Screening in early pregnancy for pre-eclampsia using Down syndrome quadruple test markers

OBJECTIVES: To estimate the screening performance of early second-trimester prenatal serum markers for Down syndrome, in screening for the development of pre-eclampsia, and analyse the uncertainty over its screening performance. METHODS: A nested case-control study was carried out on 96 women with pre-eclampsia and 5 controls for each case from among the women attending three hospitals in London for their prenatal care. Record linkage between computerized obstetric and screening databases identified women with pre-eclampsia and unaffected control women. The stored frozen serum samples collected from these pregnancies between 15 and 22 weeks' gestation were retrieved and assayed for alpha-fetoprotein (AFP), unconjugated estriol (uE(3)), total human chorionic gonadotrophin (hCG), free beta-hCG and inhibin-A. RESULTS: Pre-eclampsia was identified from the computerized obstetric records and confirmed by examination of the medical notes. In the pregnancies that went on to develop pre-eclampsia, early second trimester inhibin-A and hCG values were significantly raised and uE(3) values were significantly lowered, while AFP values were not significantly altered. Using the Quadruple test markers (AFP, uE(3), hCG (total or free beta) and inhibin-A), an estimated 34% of pregnancies that developed pre-eclampsia were detected at a 5% false-positive rate. If all the women who had pre-eclampsia in a previous pregnancy (assuming a pre-eclampsia prevalence of 4%) are considered as screen positive and the serum test is applied to the remaining women, then around 42% of pre-eclamptic pregnancies would be detected at a 6.5% false-positive rate. Pre-eclampsia screening performance using the Quadruple test markers was materially better than that using the Triple test markers. CONCLUSION: Adding screening for pre-eclampsia to an existing Down syndrome screening programme using the Quadruple test markers is simple and worthwhile. It will detect over 40% of pregnancies with pre-eclampsia at an acceptable false-positive rate (about 6%) and with minimal additional costs.     

Screening for Down's syndrome: changes in marker levels and detection rates between first and second trimesters

Objective To monitor changes with gestation in levels of alpha-fetoprotein (AFP), free beta human chorionic gonadotrophin (FβhCG) and pregnancy associated plasma protein-A (PAPP-A) in Down's syndrome pregnancies and to compare risks estimated in the first trimester with those obtained by routine screening in the second trimester for the same pregnancies.
Design In each of 47 Down's syndrome pregnancies two maternal serum samples were obtained, one in the first trimester and one in the second trimester. Comparison of marker levels with 10,600 first trimester controls and a smaller sample of second trimester controls allowed case identification criteria based on optimum marker combinations to be developed and compared directly between trimesters.
Setting Biochemical genetics laboratory.
Results FβhCG was an effective marker of Down's syndrome in both the first and second trimesters. PAPP-A levels were significantly reduced in trisomy 21 pregnancies in the first trimester only. Using a population model, these two markers in combination with maternal age gave an overall detection rate of 55% for a 5% false positive rate in the first trimester. For the paired first and second trimester samples, three of six cases classified as low risk by routine second trimester screening were classified as high risk by the first trimester screening protocol of FβhCG/PAPP-A/matemal age. However, fifteen cases identified as high risk by routine second trimester screening were classified as low risk in the first trimester, a net loss in detection of 12 cases by first trimester screening.
Conclusion The data suggest that first trimester detection rates for Down's syndrome using a combination of FβhCG and PAPP-A may vary with gestation and will be lower than those currently obtained by routine second trimester screening with AFP/hCG.     

SURUSS in perspective

BACKGROUND: Until the publication of the Serum Urine and Ultrasound Screening Study (SURUSS) report, it was difficult to compare the different antenatal screening tests for Down's Syndrome because of variations in study designs. We here present the main results from SURUSS, updated to take account of recent information on nuchal translucency in Down's Syndrome pregnancies, and discuss their implications. METHODS: SURUSS was a prospective study of 47,053 singleton pregnancies (including 101 pregnancies with Down's Syndrome) conducted in 25 maternity units. Nuchal translucency measurements were taken. Serum and urine samples collected between 9 and 13 weeks, and again between 14 and 20 weeks of pregnancy were stored. Samples from each affected pregnancy and five matched controls were tested for currently used or suggested biochemical Down's Syndrome screening markers. Pregnancies were followed up to determine the presence or absence of Down's Syndrome. For an 85% Down's Syndrome detection rate, the false-positive rate for the Integrated test (nuchal translucency and pregnancy associated plasma protein-A [PAPP-A] at 11 completed weeks of pregnancy, and alpha-fetoprotein, unconjugated oestriol [uE3], free beta or total human chorionic gonadotrophin (hCG) and inhibin-A in the early second trimester) was 0.9%, the Serum integrated test (without nuchal translucency) 2.7%, the Combined test (nuchal translucency with free beta-hCG and PAPP-A at 11 weeks) 4.3%, the Quadruple test (alpha-fetoprotein, uE3, free beta or total hCG and inhibin-A) 6.2%, and nuchal translucency at 11 weeks, 15.2%. All tests included maternal age. Using the Integrated test at an 85% detection rate, there would be six diagnostic procedure-related unaffected fetal losses following amniocentesis per 100,000 women screened compared with 35 using the Combined test or 45 with the Quadruple test. CONCLUSIONS: The Integrated test offers the most effective and safe method of screening for women who attend in the first trimester. The next best test is the Serum integrated test. The Quadruple test is the best test for women who first attend in the second trimester. There is no justification for retaining the Double (alpha-fetoprotein and hCG) or Triple (alpha-fetoprotein, uE3, and hCG) tests, or nuchal translucency alone (with or without maternal age) in antenatal screening for Down's Syndrome.     

SURUSS in perspective

BACKGROUND: Until the publication of the Serum Urine and Ultrasound Screening Study (SURUSS) report, it was difficult to compare the different antenatal screening tests for Down's Syndrome because of variations in study designs. We here present the main results from SURUSS, updated to take account of recent information on nuchal translucency in Down's Syndrome pregnancies, and discuss their implications. METHODS: SURUSS was a prospective study of 47,053 singleton pregnancies (including 101 pregnancies with Down's Syndrome) conducted in 25 maternity units. Nuchal translucency measurements were taken. Serum and urine samples collected between 9 and 13 weeks, and again between 14 and 20 weeks of pregnancy were stored. Samples from each affected pregnancy and five matched controls were tested for currently used or suggested biochemical Down's Syndrome screening markers. Pregnancies were followed up to determine the presence or absence of Down's Syndrome. For an 85% Down's Syndrome detection rate, the false-positive rate for the Integrated test (nuchal translucency and pregnancy associated plasma protein-A [PAPP-A] at 11 completed weeks of pregnancy, and alpha-fetoprotein, unconjugated oestriol [uE(3)], free beta or total human chorionic gondaotrophin (hCG) and inhibin-A in the early second trimester) was 0.9%, the Serum integrated test (without nuchal translucency) 2.7%, the Combined test (nuchal translucency with free beta-hCG and PAPP-A at 11 weeks) 4.3%, the Quadruple test (alpha-fetoprotein, uE(3), free beta or total hCG and inhibin-A) 6.2%, and nuchal translucency at 11 weeks, 15.2%. All tests included maternal age. Using the Integrated test at an 85% detection rate, there would be six diagnostic procedure-related unaffected fetal losses following amniocentesis per 100,000 women screened compared with 35 using the Combined test or 45 with the Quadruple test. CONCLUSIONS: The Integrated test offers the most effective and safe method of screening for women who attend in the first trimester. The next best test is the Serum integrated test. The Quadruple test is the best test for women who first attend in the second trimester. There is no justification for retaining the Double (alpha-fetoprotein and hCG) or Triple (alpha-fetoprotein, uE(3), and hCG) tests, or nuchal translucency alone (with or without maternal age) in antenatal screening for Down's Syndrome.     

Dimeric inhibin A as a fourth marker for Down's syndrome maternal serum screening in native Japanese women

OBJECTIVE: This study was conducted to assess the usefulness of dimeric inhibin A as a fourth marker for Down's syndrome screening in addition to AFP, hCG and uE3 markers for native Japanese women. METHODS: Serum specimens from 367 native Japanese women in the second trimester were assayed for dimeric inhibin A levels. Day specific dimeric inhibin A medians were established for gestational ages 15.0-21.9. Weekly median values for the native Japanese were compared with those of a U.S. population. Selected Japanese specimens from 15 diagnosed Down's syndrome and 3 trisomy 18 cases were also assayed for dimeric inhibin A. RESULTS: Dimeric inhibin A levels did not vary greatly over the gestational age range as expected. Median value comparison showed that native Japanese dimeric inhibin A medians are higher than the U.S. population medians by an average of 7.95%. Native Japanese dimeric inhibin A median values in this study are 1.77 times higher in Down's syndrome cases than in unaffected pregnancies. Trisomy 18 dimeric inhibin A levels show no significant difference from the unaffected pregnancies. CONCLUSIONS: This report shows for the first time that dimeric inhibin A can be informative as a fourth marker for Down's syndrome screening in native Japanese women. We expect the addition of dimeric inhibin A to a triple marker protocol will increase the accuracy of predicted risk for all pregnancies screened and increase the detection rate of Down's syndrome affected pregnancies.     

Medically assisted reproduction and second-trimester maternal serum marker screening for Down syndrome

OBJECTIVES: To evaluate the effect of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) on total hCG, free ss-hCG, AFP and unconjugated estriol (uE3) used as markers for second-trimester Down syndrome maternal serum screening. METHODS: Second-trimester maternal sera from 1515 singleton pregnancies (970 by IVF, 545 by ICSI) were compared with control sera (21 014 cases). Free ss-hCG, total hCG, AFP and uE3 were compared between the control group and the medically assisted reproduction groups. The percentages of at-risk patients (>/=1/250) were also compared. RESULTS: No differences in values of the maternal serum markers were observed between the medically assisted and control groups. When maternal age was taken into account, the screen-positive rate for Down syndrome screening did not differ between the two groups. CONCLUSION: Patients undergoing assisted reproduction techniques can be counseled for maternal serum Down syndrome screening with the same efficacy as patients with naturally conceived pregnancies.     

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).     

Sensitivity and specificity of screening for Down syndrome with alpha-fetoprotein, hCG, unconjugated estriol, and maternal age.

The sensitivity and specificity of maternal serum screening for Down syndrome with different biochemical markers were evaluated. Detection rates with different combinations of maternal serum alpha-fetoprotein (MSAFP), hCG, and unconjugated estriol (uE3) were established by retrieving and analyzing 54 serum specimens from women with confirmed Down syndrome pregnancies, compared with 657 specimens from women with normal outcomes. With a risk cutoff of 1:270 at the second trimester, the detection rate with MSAFP, hCG, and uE3 was two to three times higher than with MSAFP alone. With all three markers, the detection rate for Down syndrome increased from 50 to 77% as maternal age increased, and was 60% in a representative screened population. If uE3 was omitted, the detection rate decreased from 60 to 48%. One thousand women were screened prospectively, either with MSAFP or with all three markers prospectively, either with MSAFP or with all three markers and 4.1% with MSAFP. With the three markers, the positive predictive value for Down syndrome was 2.2% overall and as high as 5.9% in older women. Therefore, the addition of hCG and uE3 to the maternal serum screen increases the positive predictive value by 50-300%, depending on maternal age. These results confirm the efficacy of screening for Down syndrome using maternal age and three serum markers.     

Risk of fetal Down's syndrome based on maternal age and varying combinations of maternal serum markers

Serum samples from 320 women with chromosomally normal fetuses and from 50 women with fetuses affected by Down's syndrome were assayed retrospectively for human chorionic gonadotropin (hCG), pregnancy-specific β ₁ glycoprotein (SP1), alpha fetoprotein (AFP), and unconjugated estriol (uE3) between 14 and 21 weeks of gestation. Nonparametric discriminant analysis was applied to calculate Down syndrome risks on the basis of various combinations of serum parameters. At a risk threshold that falsely identifies 5% of controls as being affected, 46 to 48% of Down syndrome pregnancies were detected by combinations of hCG/AFP, hCG/AFP/uE3, and hCG/AFP/uE3/SP1 respectively. HCG, AFP, and uE3 were assayed in 652 serum samples from women who underwent amniocentesis because of maternal age (≥35 years in this prospective study). 49% of women with euploid fetal karyotype, 8 of 10 pregnancies with Down's syndrome, and 3 pregnancies with sex chromosomal anomalies were identified as being at an increased risk (>1:380). Received: 30 June 1993 / Accepted: 26 January 1994     

Second-trimester prenatal screening markers for Down syndrome in women with insulin-dependent diabetes mellitus

Published studies have shown that some serum markers used in screening for Down syndrome tend to be lower among women with insulin-dependent diabetes mellitus (IDDM). On this basis, many screening programmes adjust the marker levels to take account of this difference. Recent studies suggested that the marker levels were not different, and so adjustment may no longer be needed, possibly because of better diabetic control. Data from a prenatal screening programme for Down syndrome were examined to see whether the median values of second-trimester screening markers were still reduced in pregnant women with IDDM. A total of 366 women with IDDM singleton pregnancies without Down syndrome were identified from the screening programme at Barts from 1989 to 2002. After allowing for maternal weight, the median multiples of the median (MoM) for IDDM-unaffected singleton pregnancies were as follows: 0.88 (95% confidence interval 0.84-0.93) for alphafetoprotein (AFP), 0.95 (0.91-0.99) for unconjugated oestriol (uE3), 0.90 (0.80-1.01) for total human chorionic gonadotrophin (total hCG), 0.98 (0.88-1.08) for free beta-hCG, and 0.99 (0.89-1.10) for inhibin-A. The median levels for AFP and uE3 were statistically significantly lower in pregnant women with IDDM. The other markers were not significantly different in women with and without IDDM. There remains a case for adjusting AFP and uE3 levels in women with IDDM in prenatal screening programmes for Down syndrome.     

Cross-trimester marker ratios in prenatal screening for Down syndrome

OBJECTIVE: To examine the performance of Integrated Down syndrome screening (first- and second-trimester measurements integrated into a single screening test) when ratios of the levels of the same serum markers measured in both these trimesters (cross-trimester ratios) are added as new screening markers. METHODS: Using data from Serum Urine and Ultrasound Screening Study (SURUSS), second-trimester concentrations (in multiples of the median, or MoM) of pregnancy associated plasma protein A (PAPP-A), alphafetoprotein (AFP), unconjugated oestriol (uE(3)), human chorionic gonadotrophin (hCG) (free beta and total), and inhibin-A were divided by the first-trimester concentration to obtain a cross-trimester (CT) ratio for each analyte in 74 Down syndrome and 492 unaffected pregnancies. We identified CT ratios that improved screening performance and then, using Monte Carlo simulations, estimated the efficacy and cost effectiveness of adding them to the Integrated and serum Integrated tests. RESULTS: All the median CT ratios differed significantly between Down syndrome and unaffected pregnancies. Setting the Integrated test to achieve a 90% detection rate, the false-positive rate (FPR) was 0.7% with CT ratios for PAPP-A, uE(3), inhibin-A, and total hCG compared with 2.2% without CT ratios, a reduction of about two-thirds. Using the serum Integrated test to achieve the same 90% detection rate and the first-trimester measurements made at 11 completed weeks of pregnancy, the corresponding FPRs were 2.4 and 8.1%, a similar proportional reduction. The AFP CT ratio had little effect on screening performance. Using CT ratios did not increase the cost per Down syndrome pregnancy detected. CONCLUSION: The addition of CT ratios to an Integrated test substantially improves the efficacy and safety of prenatal screening for Down syndrome. It is cost effective and could be usefully introduced into screening programmes. Copyright (c) 2006 John Wiley & Sons, Ltd.     

Comparison of triple-risk assessment of fetal trisomy 21 including total human choriogonadotropin (hCG) or its free beta-subunit (free beta hCG)

OBJECTIVE: Second trimester total hCG and free betahCG levels in maternal serum samples of 33 pregnancies affected by fetal trisomy 21 and of 188 matched controls were compared in a retrospective study. To find out differences of discriminating efficacy by using one of these markers a multivariate discriminant analysis was performed. METHOD: Statistical evaluation was performed for hCG/free betahCG frequency distributions. Discriminant analysis was carried out using the status 'affected' or 'unaffected' as the group variable and the serum markers unconjugated estriol (uE3), alpha-fetoprotein (AFP), and alternatively, hCG or free betahCG, as discriminant variables. RESULTS: The median of free betahCG MoM values in affected pregnancies was slightly higher (1.90 MoM) than the median of total hCG MoM values (1.72 MoM) but a lower standard deviation was stated for the logarithmic hCG MoM values (SD = 0.49) compared with free betahCG MoM values (SD = 0.51). A two-tailed Student's t test revealed no significant differences of hCG and free betahCG MoM values in both the affected and unaffected pregnancies. By inclusion of free betahCG the discriminant analysis classified 26 out of 33 affected cases correctly and 45 out of 188 unaffected cases incorrectly. For the inclusion of hCG these ratios were 25/33 and 41/188, respectively. Taking in account the individual maternal age risks at a defined false-positive rate of 5% including free betahCG yielded a higher detection rate than including hCG. However, using 1:380 (age-related at-term risk of a 35-year-old woman) as a cut-off risk including hCG yielded a higher detection rate than including free betahCG. CONCLUSION: For the observed cases none of the markers, hCG or free betahCG, was superior in Down syndrome screening.