Modeling Down syndrome screening performance using first-trimester serum markers.

OBJECTIVE: To evaluate the modeled predictive value of three current screening markers (pregnancy-associated plasma protein-A (PAPP-A), free ß-human chorionic gonadotropin (free ß-hCG), and nuchal translucency (NT)) and four potential screening markers (a disintegrin and metalloprotease 12 (ADAM12), total hCG, placental protein 13 (PP13), and placental growth factor (PlGF)) for Down syndrome using different screening strategies. METHODS: All markers were measured in stored first-trimester serum of 151 Down syndrome cases and 847 controls. All marker levels were expressed as gestational age-specific multiples of the median (MoMs) and comparisons were made using the Mann-Whitney U-test. Detection rates (DRs) for fixed false-positive rates (FPRs) were modeled using different screening strategies. RESULTS: Significantly different median MoMs for Down syndrome cases compared to controls were found for PAPP-A (0.49 vs. 1.00; P < 0.0001), free ß-hCG (1.70 vs. 1.01; P < 0.0001), ADAM12 (0.89 vs. 1.00; P < 0.0001), total hCG (1.28 vs. 1.00; P < 0.0001), PlGF (0.80 vs. 1.00; P < 0.0001) and NT (1.74 vs. 1.01; P < 0.0001). The lower PP13 MoM in Down syndrome cases (0.91 vs. 1.00) was not statistically significant (P = 0.061). Adding the four new markers to the current screening strategy (i.e. first-trimester combined test) led to an increase in DR from 77% to 80% at a 5% FPR. The modeled application of a two-sample screening strategy (with some markers assessed early and others later in the first trimester) increased the DR to 89%. In a two-step contingent screening model, using an intermediate risk range of 1 in 100 to 1 in 2000 at biochemical screening (using all markers), the overall DR was 77%, but it was predicted that only 33% of women would require referral for NT measurement. CONCLUSIONS: First-trimester Down syndrome screening may be improved by adding new markers to the current screening test and by applying different screening strategies. The application of a two-sample screening model resulted in the highest predicted DR, but this should be confirmed in population-based prospective studies.

Longitudinal trends in fetoplacental biochemical markers, uterine artery pulsatility index and maternal blood pressure during the first trimester of pregnancy.

OBJECTIVE: To assess trends in levels of biochemical markers, uterine artery (UtA) pulsatility index (PI) and maternal blood pressure changes over time and study their relationships in uncomplicated first-trimester pregnancies. METHODS: The study population comprised 86 women with singleton pregnancies. In each woman, a blood sample was collected at 6-7, 8-9, 10-11 and 12-13 weeks' gestation. At the same visit blood pressure was measured and ultrasound examination was performed to measure the crown-rump length and Doppler flow velocity waveform patterns of both UtAs. Serum concentrations of pregnancy-associated plasma protein-A (PAPP-A), free ß-human chorionic gonadotropin (ß-hCG), A disintegrin and metalloprotease domain-containing protein-12 (ADAM-12), placental protein-13 (PP-13) and placental growth factor (PlGF) levels were measured in thawed specimens using an automated time-resolved fluorescence assay. Summary curves were created to describe normal ranges and trends over time. The data were analyzed with a linear mixed model with the log-transformed marker values as dependent variables. This allowed for flexible modeling of patterns over time. RESULTS: Sixty-eight pregnancies had an uneventful outcome, with the birth of an appropriate-for-gestational-age (AGA) infant. In these pregnancies serum PAPP-A, ADAM-12, PP-13 and PlGF levels increased with gestational age. The UtA-PI decreased and the mean arterial blood pressure remained constant. There were no significant correlations between maternal age, birth-weight percentile, gender and blood pressure and any of the biochemical markers. The serum markers were highly correlated with each other except for ß-hCG. A negative correlation was found between most biomarkers and UtA-PI, especially from 10 weeks onwards. Serum concentrations of ADAM-12 and PP-13 were lower in a small-for-gestational-age (SGA) subgroup born at term (n = 6), the former statistically significantly (P = 0.031), the latter non-significantly (P = 0.054), whereas UtA-PI was significantly higher (P = 0.02). Biomarker concentrations in 12 women delivering a large-for-gestational age infant did not differ from those delivering AGA neonates. CONCLUSION: There is a relationship between biochemical markers of early placentation and downstream resistance to flow in the UtAs in low-risk uncomplicated pregnancies, indicating differences in placentation. In a small series of SGA infants born at term we could demonstrate differences as compared to normal pregnancies, with potential value for screening.

Prediction of macrosomia at birth in type-1 and 2 diabetic pregnancies with biomarkers of early placentation.

OBJECTIVE: To evaluate the value of first trimester placental biomarkers (fß-hCG, PAPP-A, ADAM12, PP13 and PlGF) and fetal nuchal translucency (NT) in the prediction of macrosomia at birth in pregestational type-1 and type-2 diabetes (PGDM). DESIGN: Nested case-control study. SETTING: Routine first-trimester combined test. POPULATION: A total of 178 PGDM and 186 control pregnancies. METHODS: ADAM12, PP13 and PlGF concentrations were measured in stored first-trimester serum, previously tested for fß-hCG and PAPP-A. All concentrations were expressed as multiples of the median (MoM). Where applicable, the median MoMs of PGDM and control pregnancies were compared in relation to birthweight centiles (≤90th centile, non-macrosomic, versus >90th centile, macrosomic). Model-predicted detection rates for fixed false-positive rates were obtained for statistically significant markers, separately and in combination. MAIN OUTCOME MEASURES: Prediction of macrosomia in diabetic pregnancies. RESULTS: In the PGDM group, median ADAM12 MoM (0.88; P = 0.007) was lower than in the controls. Subgroup analyses showed that median MoMs of PAPP-A (0.65), ADAM12 (0.85), PP13 (0.81) and PlGF (0.91) were only reduced in the PGDM non-macrosomic birthweight subgroup (n = 93) compared with other weight subgroups. In the PGDM macrosomic birthweight subgroup (n = 69), MoMs of all markers were comparable with the control birthweight subgroups. The screening performance for macrosomia at birth in the PGDM group provided a detection rate of 30% for a 5% false-positive rate (FPR) and 43% for a 10% FPR. CONCLUSIONS: Macrosomia at birth in PGDM pregnancies may be predicted by normal levels of PAPP-A, ADAM12, PP13 and PlGF already in the first trimester of pregnancy. Fetal birthweight in PGDM offspring is partially determined by placental development during the first trimester of pregnancy. The present increase in fetal macrosomia may be related to better early glycemic control and placentation.

First-trimester placental protein 13 and placental growth factor: markers for identification of women destined to develop early-onset pre-eclampsia.

OBJECTIVE: To investigate the predictive value of maternal serum pregnancy-associated plasma protein A (PAPP-A), free ß subunit of human chorionic gonadotrophin (fß-hCG), placental protein 13 (PP13), placental growth factor (PlGF) and a desintegrin and metalloproteinase 12 (ADAM12), for first-trimester identification of early-onset pre-eclampsia. DESIGN: Nested case-control study. SETTING: Routine first-trimester screening for trisomy 21 in the Netherlands. POPULATION: Eighty-eight women who developed pre-eclampsia or haemolysis, elevated liver enzymes, low platelets (HELLP) syndrome before 34 weeks of gestation and 480 controls. METHODS: PP13, PlGF and ADAM12 were measured in stored first-trimester serum, previously tested for PAPP-A and fß-hCG. All marker levels were expressed in multiples of the gestation-specific normal median (MoMs). Model predicted detection rates for fixed false-positive rates were obtained for statistically significant markers alone and in combination. MAIN OUTCOME MEASURES: Development of pre-eclampsia or HELLP syndrome. RESULTS: PP13 and PlGF were reduced in women with pre-eclampsia, with medians 0.68 MoM and 0.73 MoM respectively (P < 0.0001 for both). PAPP-A was reduced (median 0.82 MoM, P < 0.02) whereas ADAM12 and fß-hCG did not differ between control women and those with pre-eclampsia. In pre-eclampsia complicated by a small-for-gestational-age fetus, all markers except fß-hCG had lower values, compared with pregnancies involving fetuses of normal weight. The model-predicted pre-eclampsia detection rate for a combination of PP13 and PlGF was 44% and 54%, respectively, for a fixed 5% and 10% false-positive rate. CONCLUSION: This study demonstrates that PP13 and PlGF in the first-trimester might be promising markers in risk assessment for early pre-eclampsia/HELLP syndrome but for an adequate screening test additional characteristics are necessary.

Distributions of current and new first-trimester Down syndrome screening markers in twin pregnancies.

OBJECTIVES: To study the distributions of pregnancy-associated plasma protein A (PAPP-A), the free beta subunit of human chorion gonadotrophin (fbeta-hCG), A Disintegrin and Metalloprotease 12 (ADAM12) and Placental Protein 13 (PP13) in first trimester twin pregnancies. METHODS: Serum marker concentrations were measured in monochorionic and dichorionic twin pregnancies and singleton controls to study differences in multiples of the gestation-specific normal medians (MoMs). RESULTS: Median PAPP-A and fbeta-hCG MoMs were 2.03 and 1.87 for monochorionic twins (n = 116) and 2.18 and 1.89 for dichorionic twins (n = 650). Furthermore, ADAM12 and PP13 MoMs were 1.66 and 1.56 for monochorionic twins (n = 51) and 1.64 and 1.53 for dichorionic twins (n = 249). No statistically significant differences between monochorionic and dichorionic twin pregnancies were found. Correlations between markers in these pregnancies did not differ from singletons. CONCLUSION: For first-trimester screening, different parameters for monochorionic and dichorionic twin pregnancies is not necessary. Furthermore, if ADAM12 and PP13 will be adopted as screening markers, the presented median MoM values, standard deviations and correlation coefficients for twin pregnancies may contribute to a proper twin risk estimation.

Placental protein 13 as a first trimester screening marker for aneuploidy.

OBJECTIVE: To determine whether Placental Protein 13 (PP13) could be an additional marker in first trimester screening for aneuploidies. METHODS: To evaluate differences in multiples of the gestation-specific normal median (MoMs), PP13 concentrations were measured in serum samples from Down syndrome, trisomy 18 and 13 affected pregnancies and euploid singleton pregnancies (four for each case matched for duration of storage, maternal weight and age). RESULTS: The PP13 MoM in Down syndrome cases (n = 153) was 0.91 [not statistically significant from controls (n = 853); P = 0.06; Wilcoxon rank sum test, two-tail]. PP13 MoMs were decreased in trisomy 18 (n = 38-median MoM 0.64; P < 0.0001) and trisomy 13 cases (n = 23-median MoM 0.46; P < 0.0001). There was a slight upward trend in MoM values of the Down syndrome cases with gestational weeks. The PP13 MoM was significantly correlated with the pregnancy associated plasma protein-A MoM and the free beta-subunit of human chorion gonadotrophin (fbeta-hCG) MoM. CONCLUSION: PP13 does not seem to be a good marker for Down syndrome. PP13 MoMs are, however, significantly lower in trisomy 18 and 13 pregnancies. The addition of PP13 to the current screening test could be valuable for improving the discrimination of aneuploid from euploid pregnancies.

Quality of nuchal translucency measurements in The Netherlands: a quantitative analysis.

OBJECTIVE: The Dutch Centre for Population Research has specified quality demands for nuchal translucency (NT) measurement in The Netherlands. We performed an analysis of the quality of NT measurement in 2005-2006 and its influence on screening performance. METHODS: This was a retrospective study of records of NT measurements (n = 27,738) obtained between January 2005 and December 2006 retrieved from the Dutch National Institute for Public Health and the Environment (RIVM). The performance of each individual operator was analyzed with regard to the quality standards, which involved calculation of operator-specific median NT-multiples of the median (MoM) values. For the entire population of operators, a curve was determined describing the relationship between crown-rump length and NT. Detection rates (DR) and false-positive rates (FPR) for Down syndrome were modeled with this new curve and compared to those originally obtained using previously published reference data. RESULTS: Only 22% of all operators met the quality requirement of performing more than 150 NT measurements per year. However, no relationship was found between the number of measurements per operator and their median NT-MoM. The mean of all operator-specific median NT-MoM values was 0.94 (target value 1.0). Overall, operators with The Fetal Medicine Foundation certificate measured a significantly higher median NT-MoM (mean of operator-specific medians, 0.98) as compared to the non-certified operators (0.92). During the study period, the monthly median NT-MoM of all operators rose steadily, from 0.86 in January 2005 to 0.96 in December 2006. Recalculation of the risk for Down syndrome after adjusting the reference NT medians using our own data led to a modeled 4% increase in DR at a 5% FPR. CONCLUSION: Improved monitoring of NT measurement put into effect during the study period seems to have led to an improvement in the accuracy of measurements. Strict quality demands, continued monitoring and scrupulous evaluation of individual operators is likely to lead to an even better performance.

ADAM12s as a first-trimester screening marker of trisomy.

OBJECTIVE: To evaluate the potential of maternal serum A Disintegrin And Metalloprotease 12-S (ADAM12s) as an additional marker for the combined test in the Dutch first-trimester national Down syndrome (DS) screening program. METHODS: Serum samples were collected between 2004 and 2007 as part of the national program. A total of 218 singleton cases of trisomy 21 (DS), 62 trisomy 18 (Edwards syndrome) and 29 trisomy 13 (Patau syndrome) were identified. All cases were matched with controls for gestation, maternal weight and maternal age. The serum concentration of ADAM12s was determined 'blind' to outcome and expressed in multiples of the gestation-specific median for controls (MoM). RESULTS: The median ADAM12s was 1.00 MoM in controls and in the DS cases at 8, 9, 10, 11, 12, 13 weeks it was 0.45 (n = 3), 0.73 (22), 0.74 (53), 0.85 (37), 0.92 (71), 1.06 (32) MoM, respectively. The median for trisomy 18 was 0.85 MoM and for trisomy 13 0.63 MoM. CONCLUSION: The ADAM12s MoM values were clearly reduced in early first-trimester for all trisomies. However, the screening performance for DS did not greatly improve adding ADAM12s. ADAM12s could be an additional biochemical marker for first-trimester screening for trisomies other than DS.

First-trimester Down syndrome screening performance in the Dutch population; how to achieve further improvement?

OBJECTIVE: To study the performance of the first-trimester combined test between 2004 and 2006 compared to a previous period to investigate changes in time and identify reasons for sub-optimal performance. METHODS: Serum samples were analysed for pregnancy-associated plasma protein A (PAPP-A) and the free beta subunit of human chorionic gonadotrophin (f beta-hCG). Nuchal translucency (NT) was measured between 10 and 14 weeks. Tests were considered screen positive, if their calculated Down syndrome (DS) risk was at least 1 in 250 at term. RESULTS: A total of 20,293 singleton pregnancies were included in the analysis. The median maternal age fell from 35.7 to 34.3 years. The overall median weight-corrected multiple of the median (MoM) values of PAPP-A and f beta-hCG were 1.12 and 1.03, respectively. The median MoM value of NT was 0.89 and increased from 0.82 to 0.96. Sixty-six DS cases were detected by the screening test. The detection rate (DR) for DS was 75.9%, with a FPR of 3.3%. CONCLUSION: The performance of the first-trimester test has improved over the years. A better performance of the NT measurement was the main reason, although NT assessment should further be improved. In addition, a better setting of the medians for the biochemical parameters may contribute to a higher DR.

Fifteen years of triple tests in The Netherlands; the life cycle of a screening test.

OBJECTIVE: This report provides an overview of 15 years prenatal screening for Down syndrome (DS). METHODS: Between 1991 and 2005, blood samples for the triple test were sent for analysis to our laboratory. Test results were considered screen-positive for neural tube defects (NTDs) if the serum alpha-1-fetoprotein > or = 2.50 MoM for singleton pregnancies or screen-positive for DS if the calculated risk was at least 1 in 250. RESULTS: As many as 42 554 tests were performed. Data on the pregnancy outcome were available for 30 290 screening tests (71.2%). In 1991, most requests (93%) came from the university hospitals; thereafter a shift toward midwives occurred. Until 2001, the number of requests rose to 3500 a year. Most samples were collected between 15 and 17 weeks of gestation. The median age of women for whom a test was requested increased from 30.5 to 34.5. The detection rate (DR) for DS remained stable over the years (80%), with a false positive rate of about 13%. The DR for Trisomy 13, 18, and NTD was 50, 68, and 70%, respectively. CONCLUSION: Based on the results of this study, the triple test may be considered a fairly good second trimester screening test. Here it is shown that health practitioners got more acquainted with the test through the years. This may have served the swift introduction of a formal national screening program that started in January 2007.

Lack of standardization in determining gestational age for prenatal screening.

OBJECTIVES: To determine whether estimation of gestational age (GA) in the context of first-trimester Down syndrome screening is standardized in the Netherlands. METHODS: This was a retrospective study, carried out between January 2005 and December 2006, of women who underwent first-trimester Down syndrome screening (n = 40,730) based on GA, maternal serum analysis and nuchal translucency (NT) measurement. Date of the last menstrual period (LMP), dating scan information including measurement of crown-rump length (CRL), NT thickness and name of the sonographer were recorded for all pregnancies. The accuracy of estimation of GA was evaluated by comparing the GA based on the LMP with that estimated from the CRL, using relevant subsets of the database. A survey of 104 sonographers was performed to further investigate the findings of the preceding analysis. RESULTS: In 44% of all first-trimester combined tests the estimation of GA was based on the dating scan; the method of determination of GA was unknown in 23%. In 15% of all cases a dating scan was recorded but was not used to provide the estimation of GA at blood sampling. Detailed analysis showed that a consistent methodology for the estimation of GA from CRL was not maintained within hospitals and obstetric practices. For a single CRL, the reported GA differed by up to 10 days. Finally, it was demonstrated that individual sonographers reported different GAs for a given CRL. CONCLUSIONS: Currently, estimation of GA in the first trimester in the Netherlands is not standardized. To improve the performance of prenatal screening for Down syndrome, estimation of GA should be based on ultrasound examination, with one nationally accepted CRL curve.