1 Department of Obstetrics and Gynaecology, Taipei Chang Gung Memorial Hospital, Taipei, 2 The Endocrine Unit, Department of Clinical Biochemistry, Harold Wood Hospital, Romford, Essex, UK and 3 Lin-Kou Chang Gung Memorial Hospital, Tau-Young, Taiwan, ROC
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Abstract |
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Key words: chromosomal abnormalities/Down's syndrome/human chorionic gonadotrophin ß-core fragment/prenatal screening/urine
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Introduction |
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Recent reports have indicated that the urine HCGßcf could be an even better marker of fetal aneuploidy than the existing serum markers in the second trimester. They found at least four-fold elevation of HCGßcf in Down's syndrome pregnancies and achieved a 6288% detection rate with a 5% false-positive rate (Cuckle et al., 1994, 1995
; Canick et al., 1995
; Iles, 1996
; Cole et al., 1997a
; Isozaki et al., 1997
). However, some authors were still uncertain of the effectiveness of using HCGßcf for Down's syndrome screening in Asians (Hayashi and Kozu, 1995
; Lam et al., 1997
) and Caucasians (Spencer et al., 1996
). Because of racial differences between Asians and Caucasians, it remains to be seen whether these urine screening strategies are equally applicable in Asians. The aim of the current study is to investigate whether maternal urine HCGßcf might be an even better marker for Asian pregnancies with fetal chromosomal abnormalities.
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Materials and methods |
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Urine samples were centrifuged and stored at 40°C prior to analysis with mean storage time of 55 and 51 weeks in Down's syndrome and normal pregnancies respectively. The HCGßcf concentrations were measured by using a commercial enzyme immunoassay kit (UGF-EIA Toa, Toagosei Co. Ltd, Tokyo, Japan) in which only the HCGßcf was specifically detected with cross-reactivity of 0.44% to the HCGß (Cole, 1995). All samples were diluted at 1:50 and 1:2500 prior to assay. To correct the variation of urine-concentrating effects, HCGßcf concentrations (ng/l) were corrected to a standard urine creatinine (Cr) concentration (mmol/l). Cr was measured with a standard Jaffe reaction procedure after a 1 in 20 urine dilution in 0.9% normal saline. Optimal smoothed gestation-specific medians of HCGßcf were calculated by weighted non-linear regression from the observed medians at each gestational week (Table I
). Considering the gestational variation of creatinine, the results were expressed in multiples of the median (MOM) for the relevant gestational week.
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Results |
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The median HCGßcf values were inversely related to the gestation in weeks in unaffected pregnancies (log median (HCGßcf) = 29.7697 + 85.3906xlog (GA) 72.6908xlog (GA)2 + 19.8169xlog (GA)3, where GA is the gestation in weeks). The median, 5th, 10th, 25th, 75th, 90th, and 95th centiles of normal controls were 1.06, 0.19, 0.28, 0.58, 3.05, 6.76, and 8.22 MOM respectively. There was a wide spread of values in the controls, exemplified by the five-fold range between the 25th and 75th centiles or by the 24-fold 10th and 90th centile range. Urine HCGßcf log MOM values fitted a Gaussian distribution in both Down's syndrome and normal pregnancies (D = 0.91, P = 0.39; and D = 1.02, P = 0.25; respectively; KolmogorovSmirnov test).
Urine HCGßcf MOM concentrations in each case of Down's syndrome pregnancies are shown in Figure 1. There were 27 of 28 [96%, 95% confidence interval (CI) 90103%] Down's syndrome cases (median 12.89 MOM, 95% CI 4.7535.75) with urine HCGßcf above the median of normal controls (1.06 MOM, 95% CI 0.911.27) and 18 of 28 (64%, 95% CI 4782%) cases at or above the 95th centile of the control values (8.22 MOM cut-off). One case of trisomy 18 (6.71 MOM) and four of five (80%) other chromosomally abnormal cases (median 2.70 MOM) had elevation of urine HCGßcf above the median of normal controls and one of five (20%) other chromosomally abnormal cases with HCGßcf concentrations at or above the 95th centile of the control values (Figure 2
).
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Discussion |
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We confirm that urine HCGßcf concentrations of Down's syndrome pregnancies is elevated in Asians, which is similar with those findings of previous studies in Asians (Hayashi and Kozu, 1995; Lam et al., 1997
) and Caucasians (Cuckle et al., 1994
, 1995
; Canick et al., 1995
; Iles, 1996
; Cole et al., 1997a
; Isozaki et al., 1997
; Kellner et al., 1997
). The median HCGßcf MOM value of Down's syndrome pregnancies in this study (12.89) was markedly higher than those of previous studies (Table II
). At a fixed 5% false-positive rate, the observed detection rate in this study (64%) was higher than previously reported results (Hayashi and Kozu, 1995
; Spencer et al., 1996
; Lam et al., 1997
) and in agreement with results of previous studies (5871%) (Cuckle et al., 1994
; Iles, 1996
; Cole et al., 1997a
; Isozaki et al., 1997
; Kellner et al., 1997
), but lower than others (Canick et al., 1995
; Cuckle et al., 1995
) (Table II
).
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Figure 2 shows the distribution of urine HCGßcf MOM concentrations from the 20 cases of trisomy 18 pregnancies in our study and the world literature. These reports confirm that urine HCGßcf concentrations were decreased in trisomy 18 pregnancies (median 0.32 MOM, range 0.022.19) (Canick et al., 1995
; Cuckle et al., 1995
; Hayashi and Kozu, 1995
; Spencer et al., 1996
; Isozaki et al., 1997
) as with serum free ß-HCG (median 0.37 MOM, range 0.270.42) in trisomy 18 pregnancies (Spencer et al., 1993
). Reduced MOM concentrations in trisomy 18 pregnancies were observed in a small number of studies with median values of 0.33 (n = 5) (Cuckle et al., 1995
) and 0.15 (n = 5) (Spencer et al., 1996
). The observations of elevated MOM value in our case (6.71) and normal values previously reported (Canick et al., 1995
) (1.09 and 1.30) are different from the previous findings. However, there were too few affected cases to make any conclusion and more work is needed to clarify this discrepant finding.
Figure 2 also demonstrates the urine HCGßcf MOM concentrations from the 22 pregnancies with chromosomal abnormalities other than trisomy 18 and 21 from our study and the world literature. There were three cases of Turner's syndrome, one case of 47,XXY, one case of 47,XXX (Cuckle et al., 1995
), two cases of triploidy (Cuckle et al., 1994
; Canick et al., 1995
), one case of trisomy 9 (Canick et al., 1995
), three cases of trisomy 13 (Canick et al., 1995
; Isozaki et al., 1997
), four cases of inversion 9, and two cases of marker chromosome (Hayashi and Kozu, 1995
). These results show that urine HCGßcf concentrations were also slightly decreased in other chromosomally abnormal pregnancies (median 0.86 MOM, range 0.0290.00). However, three of four (75%) translocation cases and one mosaic deletion case in this study had an elevated urine HCGßcf concentration. It seems that more work is needed to evaluate urine HCGßcf concentrations for their usefulness in the detection of fetal chromosomal abnormalities other than Down's syndrome.
In conclusion, the apparent advantages and encouraging results of urine HCGßcf has been thought to be a promising marker for future Down's syndrome screening. This study has demonstrated the feasibility of HCGßcf in urine screening for Down's syndrome in an Asian population. Although maternal serum screening programmes have been conducted in Taiwan or other western countries for several years, there is still a limitation in the detection rates of Down's syndrome screening. Urine screening could replace serum screening not only because of logistical advantages but increased sensitivity (Cuckle et al., 1995; Cole et al., 1997a
). However, although the screening performance using urine markers will not surpass the 8090% detection rate achievable in the first trimester using nuchal translucency and serum biochemical markers (Spencer et al., 1999
), urine markers could be useful in the area where Down's syndrome screening is not available in the first trimester. Recently, urine HCGßcf has been reported in combination with other analytes and ultrasound to improve the performance of a screening test (Bahado-Singh et al., 1998
, 1999
). However, a large-scale study is needed to survey the performance of urine screening for Down's syndrome and other chromosomal abnormalities in an Asian population.
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Acknowledgments |
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Notes |
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References |
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Submitted on February 2, 1999; accepted on April 23, 1999.