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.     

Maternal serum free beta-hCG and PAPP-A in fetal sex chromosome defects in the first trimester

We have studied maternal serum free beta-hCG and PAPP-A, and fetal nuchal translucency (NT) in a series of 46 cases of fetal Turner's syndrome, 13 cases of other sex chromosomal anomalies and compared these with 947 control pregnancies in the first trimester. In cases of Turner's syndrome (45,X) the median fetal NT was significantly higher than in controls (4.76 MoM), the median PAPP-A was significantly lower (0.49 MoM), whilst the free beta-hCG was not significantly different (1.11 MoM). For NT, 93% (43/46) of cases were equal to or greater than the 95th centile of controls, for PAPP-A 35% (16/46) of cases were less than or equal to the 5th centile of controls and for free beta-hCG 15% (7/46) of cases were equal to or greater than the 95th centile of controls. For other sex chromosomal anomalies (47XXX, XXY, XYY) the median NT was increased (2.07 MoM) whilst PAPP-A was not significantly decreased (0.88 MoM) and free beta-hCG was not significantly different (1.07 MoM) from controls. Using a previously derived multivariate risk algorithm for trisomy 21, incorporating NT, PAPP-A, free beta-hCG and maternal age, 96% of the Turner's cases and 62% of the other sex chromosomal anomalies would have been identified.     

A first trimester trisomy 13/trisomy 18 risk algorithm combining fetal nuchal translucency thickness,maternal serum free beta-hCG and PAPP-A

This study examines 45 cases of trisomy 13 and 59 cases of trisomy 18 and reports an algorithm to identify pregnancies with a fetus affected by trisomy 13 or 18 by a combination of maternal age fetal nuchal translucency (NT) thickness, and maternal serum free beta-hCG and PAPP-A at 11-14 weeks of gestation. In this mixed trisomy group the median MoM NT was increased at 2.819, whilst the median MoMs for free beta-hCG and PAPP-A were reduced at 0.375 and 0.201 respectively. We predict that with the use of the combined trisomy 13 and 18 algorithm and a risk cut-off of 1 in 150 will for a 0.3% false positive rate allow 95% of these chromosomal defects to be identified at 11-14 weeks. Such algorithms will enhance existing first trimester screening algorithms for trisomy 21.     

Second trimester levels of pregnancy associated plasma protein-A in cases of trisomy 18

In a study of 70 cases of trisomy 18 and 450 matched controls in the second trimester we have measured the maternal serum levels of the analytes alpha feto protein (AFP), free beta-human chorionic gonadotrophin (hCG) and pregnancy associated plasma protein-A (PAPP-A). We have found the median multiple of the median (MoM) of maternal serum free beta-hCG to be significantly lower (0.327) than normal, as was the level of AFP (0.600). Levels of PAPP-A were reduced even further (0.108). Of the markers associated with trisomy 18 at this time PAPP-A was the most discriminatory, being lower than the 5 per cent centile of normal in 93 per cent of cases, compared with 57 per cent of cases for free beta-hCG and 32 per cent of cases for AFP. Combining free beta-hCG and PAPP-A or all three markers with maternal age would have the ability to detect 74 per cent of cases at a 0.5 per cent false positive rate (or 64 per cent at a 0.1 per cent false positive rate). Unlike in cases of trisomy 21, the low PAPP-A values observed in the first trimester are continued into the second trimester. Whether the good discriminatory power of PAPP-A can be realized in second trimester screening programmes will depend on developing two stage screening algorithms. This approach is unlikely to be better than the excellent detection rates achievable with free beta-hCG, PAPP-A and nuchal translucency in the first trimester.     

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.     

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

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

Maternal serum hyperglycosylated human chorionic gonadotrophin (HhCG) in the first trimester of pregnancies affected by Down syndrome,using a sialic acid-specific lectin immunoassay

In a series of 54 cases of pregnancies complicated by Down syndrome and 224 unaffected pregnancies we examined maternal serum levels of hyperglycosylated human chorionic gonadotrophin (HhCG) in samples collected in the first trimester (11-13 weeks) using a sialic acid-specific lectin immunoassay. We compared these levels with those of other potential first trimester serum markers [free beta-hCG, pregnancy-associated plasma protein A (PAPP-A) and total hCG (ThCG)] and modeled detection rates and false-positive rates of various biochemical markers in conjunction with fetal nuchal translucency (NT) and maternal age using an maternal age standardized population. Maternal serum HhCG in cases of Down syndrome were significantly elevated (median MoM 1.97) with 24/54 (44%) of cases above the 95th centile for unaffected pregnancies. Free beta-hCG was also elevated (median MoM 2.09) with 33% of cases above the 95th centile. PAPP-A levels were reduced (median MoM 0.47) with 38% below the 5th centile. ThCG levels, whilst elevated (median MoM 1.34), had only 20% of cases above the 95th centile. Maternal serum HhCG levels were not correlated with fetal NT but showed significant correlation with ThCG and free beta-hCG and with PAPP-A in the Down syndrome group (r=0.536). Maternal serum HhCG levels in cases with Down syndrome had a significant correlation with gestational age, increasing as the gestation increased. When HhCG was combined together with fetal NT, PAPP-A and maternal age, at a 5% false-positive rate the modeled detection rate was 83%, some 6% lower than when free beta-hCG was used and some 4% better than when ThCG was used. Maternal serum HhCG is unlikely to be of additional value when screening for Down syndrome in the first trimester.     

Maternal serum biochemistry at 11-13(+6) weeks in relation to the presence or absence of the fetal nasal bone on ultrasonography in chromosomally abnormal fetuses: an updated analysis of integrated ultrasound and biochemical screening

BACKGROUND: Screening for trisomy 21 by a combination of maternal age, fetal nuchal translucency (NT) thickness and maternal serum free beta-hCG and pregnancy associated plasma protein-A (PAPP-A) at 11-13(+6) weeks of gestation is associated with a detection rate of 90%, for a false-positive rate of 5%. Recent evidence suggests that in about 70% of fetuses with trisomy 21 the nasal bone is not visible at the 11-13(+6) week scan and that the frequency of absence of nasal bone differs in different ethnic groups. In addition, there is a relationship between absent nasal bone and nuchal translucency thickness. In a preliminary study we showed that while PAPP-A levels were lower and free beta-hCG levels were higher in trisomy 21 fetuses with an absent nasal bone, this difference was not statistically different. In fetuses with trisomy 13 and trisomy 18, there is also a high (57 and 67%) incidence of an absent nasal bone. The aim of this present study was to extend our examination of whether the level of maternal serum biochemical markers is independent of the presence or absence of the nasal bone in cases with trisomy 21 and to ascertain if any differences exist in cases with trisomies 13 and 18. METHODS: This study data comprised 100 trisomy 21 singleton pregnancies at 11-13(+6) weeks of gestation from our previous study and an additional 42 cases analysed as part of routine OSCAR screening. A total of 34 cases with trisomy 18 and 12 cases with trisomy 13 were also available. Ultrasound examination was carried out for measurement of fetal NT and assessment of the presence or absence of the fetal nasal bone. Maternal serum free beta-hCG and PAPP-A were measured using the Kryptor rapid random access immunoassay analyser (Brahms Diagnostica AG, Berlin). The distribution of maternal serum free beta-hCG and PAPP-A in chromosomally abnormal fetuses with absent and present nasal bone was examined. RESULTS: The nasal bone was absent in 29 and present in 13 of the new trisomy 21 cases and in 98 (69%) and 44 respectively in the combined series. For the trisomy 18 cases, the nasal bone was absent in 19 (55.9%) cases and in 3 (25%) of cases of trisomy 13. There were no significant differences in median maternal age, median gestational age, NT delta, free beta-hCG MoM and PAPP-A MoM in trisomy 21 fetuses with and without a visible nasal bone, and similarly for those with trisomies 13 or 18. For a false-positive rate of 5%, it was estimated that screening with the four markers in combination with maternal age would be associated with a detection rate of 96% of cases with trisomy 21. For a false-positive rate of 0.5%, the detection rate was 88%. CONCLUSIONS: There is no relationship between an absent fetal nasal bone and the levels of maternal serum PAPP-A or free beta-hCG in cases with trisomies 13, 18 or 21. An integrated sonographic and biochemical test at 11-13(+6) weeks can potentially identify about 88% of trisomy 21 fetuses for a false-positive rate of 0.5%.     

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.     

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.     

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

BACKGROUND: ADAM12 (a disintegrin and metalloprotease 12) is a placentally derived glycoprotein that appears to be involved in growth and differentiation. The maternal serum concentration of ADAM12 appears to be a very good marker of trisomy 21 in the early first trimester when levels are reduced, and in the second trimester around 16-18 weeks levels are elevated. One small preliminary study of first trimester pregnancies with trisomy 18 found reduced levels in the maternal serum, and we examine herein the potential of ADAM12 as a marker of trisomy 18 in both the first and second trimester of pregnancy. MATERIALS AND METHODS: The concentration of ADAM12 was determined by a time-resolved immunofluorometric assay in 132 first and 12 second trimester cases of trisomy 18, and 389 first and 341 second trimester gestational age-matched control pregnancies. Medians of normal pregnancies were established by polynomial regression and used to determine the population distribution parameters for the trisomy 18 and control groups. Correlation with previously established pregnancy-associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin (beta-hCG) multiples of the median (MoMs) and nuchal translucency thickness (NT) MoM were determined and used to model the performance of first trimester screening with ADAM12 in combination with other first trimester markers. RESULTS: The maternal serum concentration of ADAM12 in the first trimester was significantly reduced with a median MoM of 0.829 (p < 0.001) and a mean log10 MoM SD of 0.2663 compared to 0.3353 in the controls. In the second trimester small series ADAM12 was significantly increased with a median MoM of 2.09 (p = 0.001) and a mean log10 MoM SD of 0.2607 compared to 0.4318 in controls. There was a significant correlation of ADAM12 MoM with gestational age (r = 0.510) in trisomy 18 cases, and the median MoM increased from 0.51 at 10 weeks to 1.28 at 13 weeks and 2.09 across the 14-18 week window. ADAM12 was correlated with PAPP-A (r = 0.1918) in the first trimester of cases with trisomy 18 but less so with NT (r = 0.1594) and free beta-hCG (r = 0.0938). Modeled detection rates incorporating ADAM12, free beta-hCG, and NT were 92% at 1% false positive rate (88% at 0.5%) A combination of all four markers had a detection rate of 96.5% at a false positive rate of 1% (95% at 0.5%). CONCLUSION: ADAM12 may be a useful addition to early screening for trisomy 18 alongside other chromosomal anomalies, particularly if biochemical screening can occur before 10 weeks.     

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.     

The influence of fetal sex in screening for trisomy 21 by fetal nuchal translucency, maternal serum free beta-hCG and PAPP-A at 10-14 weeks of gestation

In a study of 2923 normal pregnancies and 203 pregnancies affected by trisomy 21 we have shown a significant difference in the median MoM of the markers: fetal nuchal translucency, maternal serum free beta-hCG and PAPP-A in the presence of a female fetus compared with a male fetus. For maternal serum free beta-hCG levels are higher by 15% if the fetus is chromosomally normal and by 11% if the fetus has trisomy 21. For maternal serum PAPP-A the levels in chromosomally normal fetuses are 10% higher in the presence of a female fetus and 13% higher if the fetus has trisomy 21. In contrast, fetal nuchal translucency is 3-4% lower in both chromosomally normal and trisomy 21 female fetuses. The consequence of such changes when screening for trisomy 21 will be a reduction in the detection rate in female fetuses by a factor of 1-2%. Correction of risk algorithms for fetal sex, however, is probably not feasible, since ultrasound detection of fetal sex is only 70-90% accurate in the 10-14 week period.     

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

BACKGROUND: Screening for trisomy 21 by a combination of maternal age, fetal nuchal translucency (NT) thickness and maternal serum free beta-hCG and pregnancy-associated plasma protein-A (PAPP-A) at 11 to 14 weeks of gestation is associated with a detection rate of 90% for a false-positive rate of 5%. Recent evidence suggests that in about 70% of fetuses with trisomy 21, the nasal bone is not visible at the 11th- to 14th-week scan (Cicero et al., 2001). The aim of this study was to examine whether fetal NT thickness and the level of maternal serum biochemical markers is independent of the presence or absence of the nasal bone, and to estimate the performance of a screening test that integrates the two sonographic and the two biochemical markers. METHODS: This was a retrospective case-control study comprising 100 trisomy 21 and 400 chromosomally normal singleton pregnancies at 11 to 14 weeks of gestation. Ultrasound examination was carried out for measurement of fetal NT and assessment of the presence or absence of the fetal nasal bone. Maternal serum free beta-hCG and PAPP-A were measured using the Kryptor rapid random-access immunoassay analyser (Brahms Diagnostica GmbH, Berlin). The distribution of fetal NT, maternal serum free beta-hCG and PAPP-A in trisomy 21 fetuses with absent and present nasal bone was examined. RESULTS: The nasal bone was absent in 69 and present in 31 of the trisomy 21 fetuses. There were no significant differences in median maternal age, median gestational age, NT delta, free beta-hCG MoM and PAPP-A MoM in trisomy 21 fetuses with and without a visible nasal bone. For a false-positive rate of 5%, it was estimated that screening with the four markers in combination with maternal age would be associated with a detection rate of 97%. For a false-positive rate of 0.5%, the detection rate was 90.5%. CONCLUSIONS: An integrated sonographic and biochemical test at 11 to 14 weeks can potentially identify about 90% of trisomy 21 fetuses for a false-positive rate of 0.5%.     

Second-trimester levels of pregnancy-associated plasma protein-A and free beta-hCG in pregnancies with trisomy 13

OBJECTIVE: To examine the levels of free beta-human chorionic gonadotrophin (free beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A) in second-trimester maternal serum from pregnancies affected by trisomy 13 and compare these with the known reduced levels of these markers in first-trimester cases in an attempt to better understand the pathophysiology of changes in marker levels in chromosomally abnormal pregnancies between the first and second trimester. METHODS: Using the Kryptor immunoassay system, we measured free beta-hCG and PAPP-A in 32 singleton pregnancies affected by trisomy 13 between 14 and 20 weeks of gestation. Using medians established in a previous study, these results were compared against 450 normal singleton pregnancies over the same gestational range. The data were combined with data from 82 cases of trisomy 13 previously examined in the first trimester (11-13 weeks) and an analysis of analyte trend was performed. RESULTS: The median free beta-hCG in multiples of the appropriate gestational median (MoM) in the second-trimester samples was not significantly different from the controls (1.15 (95% CI 0.827-1.651) vs 1.00). The median PAPP-A MoM in the second-trimester samples was significantly lower (p<0.001) than in controls (0.25 (95% CI 0.164-0.373) vs 1.00). Seventy-eight percent of cases were below the 5th centile of normal for PAPP-A. The combined cases in the first trimester had a median free beta-hCG MoM of 0.58 (95% CI 0.454-0.668) and a median PAPP-A MoM of 0.26 (95% CI 0.218-0.320). For PAPP-A, there was no significant change in median across the gestational period of 11 to 20 weeks, whilst for free beta-hCG, there was a significant increase with gestation (r=0.458, p<0.001). CONCLUSIONS: Although PAPP-A levels are reduced in trisomy 13 pregnancies in the second trimester, this isolated lower marker value is unlikely to be of value in screening for trisomy 13 in the second trimester. The aetiology of reduced levels of PAPP-A in cases with trisomy 13 may be similar to that in cases with trisomy 18, but different from that in cases with trisomy 21 since the temporal pattern in trisomies 13 and 18 are different from that in trisomy 21.     

Screening for chromosomal anomalies in the first trimester: does repeat maternal serum screening improve detection rates?

OBJECTIVE: To assess the within person biological variability of first trimester maternal serum biochemical markers of trisomy 21 across the 10-14 week gestational period. To evaluate whether repeat sampling and testing of free beta-hCG and PAPP-A during this period would result in an improved detection rate. METHODS: Women presenting at the first trimester OSCAR clinic have blood collected prior to ultrasound dating and nuchal translucency measurement. All samples are analysed for free beta-hCG and PAPP-A before an accurate estimate of gestation is available. In 10% of cases the gestation is prior to the minimum time for NT measurement (11 weeks) and these women are rebooked for a repeat visit to the clinic at the appropriate time. Our fetal database was interrogated to obtain cases in which two maternal blood samples had been collected and analysed in the 10-14 week period. Using data from the marker correlations and statistical modelling, the impact of repeat testing on detection rate for trisomy 21 at a fixed 5% false positive rate, was assessed. RESULTS: 261 pairs of data were available for analysis collected over a 3 year period. The correlation between free beta-hCG in sample 1 and sample 2 was 0.890 and that for PAPP-A was 0.827. The average within person biological variation for free beta-hCG was 21% and 32% for PAPP-A. The increase in detection rate when using both sets of marker data was 3.5% when using serum biochemistry and maternal age, and 1.3% when using nuchal translucency, serum biochemistry and maternal age. CONCLUSION: Repeat sampling and testing of maternal serum biochemical markers is unlikely to substantially improve first trimester screening performance.     

Comparison of serum markers in first-trimester down syndrome screening

OBJECTIVE: To estimate patterns of total hCG and inhibin A levels in the late first trimester of Down syndrome pregnancies, compare them with that of free beta-hCG, and assess screening performance of these markers individually and in combination with pregnancy-associated plasma protein-A (PAPP-A) and nuchal translucency. METHODS: Seventy-nine matched case-control sets of maternal serum samples (each Down syndrome case matched to 5 controls) from 11 through 13 completed weeks of gestation were taken from the sample bank of the First and Second Trimester Evaluation of Risk Consortium, a population-based study, and assayed for levels of free beta-hCG, total hCG, and inhibin A. Distribution characteristics and correlations of the multiples of the median values were estimated in cases and controls. Screening performance for each marker, alone and in combination with PAPP-A, nuchal translucency, and maternal age, was calculated. RESULTS: Median multiples of the median levels of free beta-hCG, total hCG, and inhibin A in cases were more elevated as gestation increased from 11 to 13 weeks, with univariate detection rates of 31%, 23%, and 29%, respectively, at a 5% false-positive rate. At 12 weeks, the multivariate detection rates at a 5% false-positive rate for nuchal translucency and PAPP-A (with maternal age) with either free beta-hCG, total hCG, or inhibin A were 84%, 83%, and 85%, respectively. The improvement in performance from nuchal translucency and PAPP-A to any of the three-marker tests was significant, while performance of any of the three-marker combinations was not significantly different from each other. CONCLUSION: Although levels of free beta-hCG in affected pregnancies were higher earlier than the levels of either total hCG or inhibin A, there was no significant difference in screening performance when either of the three markers was used with nuchal translucency and PAPP-A at 11-13 weeks of pregnancy. LEVEL OF EVIDENCE: II-2.     

The influence of maternal insulin-dependent diabetes on fetal nuchal translucency thickness and first-trimester maternal serum biochemical markers of aneuploidy

OBJECTIVE: To evaluate the influence of maternal insulin dependent diabetes mellitus (IDDM) on maternal serum free beta-hCG, PAPP-A and fetal nuchal translucency (NT), thickness at 11 to 13(+6) weeks of gestation in a large cohort of women screened prospectively for chromosomal anomalies. METHODS: Information on maternal IDDM status, maternal serum biochemical marker levels and fetal NT were collected from the prenatal screening computer records in two first-trimester screening centres. In total the control group included 33 301 pregnancies of which 16 366 had NT and maternal serum biochemistry results and 16 305 with NT only. The IDDM group included 195 pregnancies of which 79 had NT and maternal serum biochemistry results and 127 with NT only. The median maternal weight corrected free beta-hCG and PAPP-A, expressed as multiple of the median (MoM), and fetal NT, expressed as delta values, in the IDDM and non-IDDM groups were compared. RESULTS: There were no significant differences between the IDDM and non-IDDM groups in median maternal weight corrected free beta-hCG (IDDM 0.87 MoM, 95% Confidence Interval 0.75 to 1.16 MoM, non-IDDM 1.00 MoM), median maternal weight corrected PAPP-A (IDDM 1.02 MoM, 95% Confidence Interval 0.83 to 1.05 MoM, non-IDDM 1.01 MoM), or mean delta NT (IDDM 0.0358 mm, non-IDDM 0.0002 mm). CONCLUSIONS: In pregnancies with maternal IDDM, first-trimester screening for chromosomal defects does not require adjustments for the measured fetal NT. However, more data are required before the possible reduction in maternal serum free beta-hCG and the reduction of PAPP-A suggested by the published world series can be considered sufficiently important to take into account in the calculation of risks for chromosomal defects.     

Screening for adverse pregnancy outcome by ductus venosus Doppler at 11-13+6 weeks of gestation

OBJECTIVE: To estimate the independent contribution of abnormal flow in the ductus venosus at 11 to 13+6 weeks of gestation in the prediction of major fetal abnormalities and fetal death. METHODS: This was a prospective assessment of singleton pregnancies by maternal history, serum free beta-hCG, pregnancy-associated plasma protein A (PAPP-A), fetal nuchal translucency thickness, and ductus venosus Doppler. The patients were subdivided into five groups: normal outcome (n=10,120), miscarriage or fetal death (n=185), abnormal karyotype (n=95), and major cardiac (n=20) or noncardiac defect (n=70). Regression analysis was performed to determine the significance of the contribution to adverse outcome of reversed a-wave in the ductus venosus, maternal characteristics, fetal delta nuchal translucency, maternal serum log PAPP-A multiples of the median, and log free beta-hCG multiples of the median. RESULTS: The prevalence of reversed a-wave was significantly higher in the groups with miscarriage or fetal death (10.8%), abnormal karyotype (62.1%), and fetal cardiac defect (25.0%) than in the normal outcome group (3.7%), but not noncardiac defect (4.3%). An adverse outcome was observed in 2.7% of the fetuses with nuchal translucency at or below the 95th centile (in 2.6% of those with normal a-wave and in 7.0% of those with reversed a-wave) and in 19.3% of the fetuses with nuchal translucency above the 95th centile (in 8.9% of those with normal a-wave and in 70.9% of those with reversed a-wave). CONCLUSION: Reversed a-wave is associated with increased risk for chromosomal abnormalities, cardiac defects, and fetal death. However, in about 80% of cases with reversed a-wave, the pregnancy outcome is normal.     

Combined measurement of fetal nuchal translucency, maternal serum free beta-hCG, and pregnancy-associated plasma protein A for first-trimester Down's syndrome screening.

PURPOSE: It has been proposed that first-trimester Down's syndrome screening has a higher detection rate compared to second-trimester biochemical screening. This study investigated the accuracy of Down's syndrome screening during gestational weeks 10 to 13 using the combination of fetal nuchal translucency (NT) measurement with maternal serum concentrations of free beta-human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A). METHODS: A total of 1,514 women with singleton pregnancies were enrolled in this study. Fetal NT was measured using the criteria published by the Fetal Medicine Foundation. Maternal serum concentrations of free beta-hCG and PAPP-A were determined by microtiter-plate ELISA. Down's syndrome risk was calculated using multivariate Gaussian distribution and Alpha software. RESULTS: Seventeen (1.12%) of the 1514 screened pregnancies had a fetal NT of at least 3 mm, and 41.2% of these had a poor pregnancy outcome, including four fetal aneuploidies. The odds of a fetal aneuploidy when the NT was greater than 2.0 multiples of median (MoM) was 90, when serum PAPP-A concentration was less than 0.45 MoM, it was 8.6, and when serum free beta-hCG concentration was greater than 2.2 MoM, it was 4.7. Using a risk cut-off level of 1 in 400, nine of 10 fetal aneuploidies were identified with a 4.7% false-positive rate, including two with trisomy 21, one with trisomy 18, and three with Turner's syndrome. CONCLUSIONS: This study demonstrated that Down's syndrome screening using the combined test in the first trimester had a higher detection rate than that of serum screening in the second trimester. Implementation of NT measurement in the first trimester provides substantial advantages for Down's syndrome detection and early diagnosis of fetal structural abnormalities.