Principles of screening.

Over the past several decades, the principles by which screening tests are performed have slowly been developed and refined. The key distinction for the clinician to understand is the difference between diagnostic tests, which give a definitive answer, and screening tests, which identify who among the low-risk population is at high risk.

Determinants of parental decisions after the prenatal diagnosis of down syndrome: bringing in context.

This article develops the concept of decision context to refer to the combinations of factors that are important in understanding and predicting termination decisions after a prenatal diagnosis of trisomy 21. Four factors are examined: maternal age, gestational age, prior voluntary abortion, and existing children. The cases were studied at the Wayne State University's Reproductive Genetics Clinic. Qualitative comparative analysis, a technique specifically designed for examining the impact of combinations of factors, is used to isolate influential decision contexts. Odds and odds ratios are used to pinpoint outcome differences among different decision contexts. Four alternative decision contexts are especially conducive to choosing to terminate a pregnancy. Two of these involve women of any age and are formed from combinations of gestational age and existing children (existing children and low gestational age, and no children combined with late gestational age). Older women who have not had an abortion and who discover the trisomy 21 anomaly early are likely to choose termination. Younger women who have had an abortion are also likely to choose termination. Our data suggest there are added layers of complexity to patients' decisions that derive from combinations of conditions. An additional, strong implication is that qualitative comparative analysis may be particularly useful in understanding such complexity.

Fiscal impact of a potential legislative ban on second trimester elective terminations for prenatally diagnosed abnormalities.

This study was designed to determine the fiscal impact of a theoretical legislative ban on elective terminations for prenatally diagnosed abnormalities at Hutzel Hospital/Wayne State University. A fiscal comparison was completed for patients who had second trimester elective terminations for prenatally diagnosed abnormalities versus not allowing the procedure. An eight-year database of genetics cases and hospital and physician cost estimates for performing elective terminations for prenatally diagnosed abnormalities, and published reports of the average lifetime costs per selected birth defects, were used to calculate the net cost. The estimated lifetime cost for an average cohort year of a legislative ban on elective terminations for prenatally diagnosed abnormalities was found to be at least $8.5 million for patients treated at Hutzel Hospital. Extrapolated, a similar ban on second trimester elective terminations would have a net cost of $74 million in Michigan and $2 billion annually in the United States.

Molecular and fetal tissue biopsy capabilities are needed to maximize prenatal diagnosis of junctional epidermolysis bullosa: fetal skin biopsy using a 1-mm microendoscope.

OBJECTIVE: To describe a minimally invasive micro-endoscopic technique for fetal skin biopsy and direct examination for a lethal skin condition. MATERIALS AND METHODS: Direct fetoscopic examination of a fetus was undertaken along with full thickness skin biopsies at 19 weeks' gestation. RESULTS: No phenotypic expressions of the lethal condition were visualized and six full thickness skin biopsies were collected. Pathological examination revealed normal skin structures not consistent with junctional epidermolysis bullosa (JEB). CONCLUSION: Minimally invasive examination with the 1 mm endoscope allows direct fetal phenotypic evaluation, full thickness skin biopsies, with risks similar to amniocentesis.

Maternal age specific risk rate estimates for Down syndrome among live births in whites and other races from Ohio and metropolitan Atlanta, 1970-1989.

Our primary objective was to estimate, by one year and five year intervals, maternal age specific risk rates for Down syndrome among whites and among other races from two different populations, metropolitan Atlanta and south west Ohio, using live birth and prenatally diagnosed cases ascertained during 1970-1989. The five year estimates were also calculated separately for each of the five four year periods during these 20 years. Additionally, we compared two different methods of estimating these risk rates by using a third population of whites, and compared two different statistical methods of smoothing the risk rates. The results indicate good agreement between the metropolitan Atlanta and south west Ohio estimates within races, but show a statistically significant difference between the two race categories. Because 86% of live births in the "other races" category in the combined population are to blacks, these data may be seen as the first estimates of maternal age specific risk rates for Down syndrome among blacks calculated by one year intervals. We found excellent agreement in the risk rate estimates among the five four year time periods, between the estimates obtained by using the two different methods of estimation, and between the estimates obtained using the two different methods of statistical smoothing. Our estimated risk rates for white women in their 20s strongly reinforce those from previous studies currently being used for genetic counselling purposes. While we did find somewhat higher rates for women under 20, and increasingly higher rates for those over 30 years of age, these differences are not substantial. Thus, this study in general supports the risk rates estimated from data collected mostly during the 1960s and 1970s.

Precise gaussian distribution functions of maternal serum alpha-fetoprotein and free beta-subunit of human chorionic gonadotropin for trisomy 21 screening: improved accuracy for patient counseling.

OBJECTIVE: Gaussian equation curves are used to generate baseline curves against which a priori maternal age Down syndrome risks are adjusted to develop likelihood ratios for individual patients. We sought to evaluate the accuracy of these calculations, minimize the affects of outliers, and to make improvements. STUDY DESIGN: Gaussian distribution functions were used to investigate the best model for alpha-fetoprotein and free beta-human chorionic gonadotropin multiples of the median with use of nonlinear regressions. Parameters from distribution functions can be used to compute a more precise likelihood ratio for the decision logic for trisomy 21. A total of 58,297 normal cases and 348 cases of trisomy 21 were computed. RESULTS: Log normal distribution functions generated by nonlinear regression produced excellent but exaggerated goodness of fit R2 to the frequency distributions of the data. For normal cases values were as follows (in mean, SD, and R2, respectively): log alpha-fetoprotein -0.07199, 0.15681, and 0.9970; log beta-human chorionic gonadotropin -0.15203, 0.24284, and 0.9987. For trisomy 21 cases the values were (in mean, SD, and R2, respectively) for log alpha-fetoprotein -0.19303, 0.15802, and 0.9828 and for log beta-human chorionic gonadotropin 0.19996, 0.29760, and 0.9669. Distributions reconstructed with use of statistical means and SDs generated goodness of fit R2 from 0.585 to 0.914. Use of means and SDs derived from distribution functions increased the R2 to 0.855 and 0.999. The change in the model produces, at a 5% false-positive rate, a sensitivity of 57.18% (199/348). A 1 in 113 cutoff point risk is obtained and is tighter than the 1 in 251 without the distribution functions, as versus 1 in 270 by age calculations alone. CONCLUSIONS: Our data suggest that (1) normality of log transforms of alpha-fetoprotein and normality of log transforms of beta-human chorionic gonadotropin are reasonable models, (2) distribution functions can minimize the effect of outliers, which produces more realistic risk estimates, and (3) the effect of distribution functions versus standard mean and SDs cannot automatically be extrapolated to other parameters, which must be tested individually.

Urinary beta-core fragment as a predictor of abnormal pregnancy at 4-6 weeks' gestation.

Currently, transvaginal ultrasound and serial serum beta-hCG measurements are used to differentiate normal versus abnormal gestations in the first trimester of pregnancy. These techniques have been found to be ineffective when the gestations are earlier than 6 weeks. This study was conducted to determine if urinary beta-core fragment, the urine degradation product of beta-hCG, could be used to distinguish normal from abnormal gestations between 4 and 6 weeks. Urine samples were obtained from 27 patients on initial presentation to the emergency room or outpatient settings with gestations at 4-6 weeks by sure last menstrual period. The urine was then frozen at -40 degrees C and sent for beta-core assay analysis. Eighteen women with normal intrauterine pregnancies and nine abnormal pregnancies, including ectopics and spontaneous abortions, were studied. Pearson correlations were performed with a p < 0.05 considered significant. In the normal gestations, there was a positive correlation between beta-core fragment and gestational age at 4-6 weeks (r = 0.461, p < 0.05). This correlation was not evident in abnormal gestations (r = 0.360, p = 0.34). In early pregnancy, beta-core fragment correlates positively with gestational age which is not apparent in abnormal counterparts. This finding suggests that urinary beta-core fragment may be a promising marker to differentiate normal early pregnancies from abnormal gestations.

Isolated unilateral fetal pleural effusion: the role of sonographic surveillance and in utero therapy.

OBJECTIVE: To discuss the necessity of close sonographic surveillance of small, isolated fetal pleural effusions as well as the selection criteria and benefits of in utero therapy utilizing thoracoamniotic shunts. METHODS: High-resolution ultrasound, fetal echocardiography, amniocentesis for viral cultures, cordocentesis, and thoracocentesis were performed to evaluate the underlying etiology of a unilateral pleural effusion. A Rodeck Rocket shunt was placed following sudden, rapid progression of the effusion and onset of severe fetal hydrops. RESULTS: Placement of the thoracoamniotic shunt resulted in near-complete drainage of the pleural effusion with normalization of intrathoracic anatomic relationships, subsequent complete resolution of fetal hydrops, and excellent postnatal outcome. CONCLUSIONS: Apparently stable, small pleural effusions can progress rapidly to severe hydrops and need to be followed closely. In appropriately evaluated and selected cases, thoracoamniotic shunt placement may result in resolution of fetal hydrops and prevent intrauterine fetal death.

An automated image analysis method for the measurement of neutrophil alkaline phosphatase in the prenatal screening of Down syndrome.

OBJECTIVES: (1) To develop an image analysis method for the measurement of neutrophil alkaline phosphatase (NAP); (2) To establish a correlation of urea-resistant fraction of NAP (URNAP)/NAP scoring between the manual and automated methods, and (3) to assess the value of URNAP/NAP in the prenatal screening of Down syndrome. STUDY DESIGN: Slides from 15 unaffected controls were blindly scored by both methods. The Pearson test was used for correlation analysis. Slides from 15 Down syndrome pregnancies and 25 unaffected controls were scored manually. RESULTS: A coefficient r = 0.93 was obtained comparing the URNAP/NAP scores generated by the two methods. Average time for scoring by the automated method was 8 min. The median URNAP/NAP values for Down syndrome and unaffected controls were 112/86.1 and 51/51.5, respectively. CONCLUSIONS: Scores obtained by both methods highly correlate. Automated scoring is threefold faster. Down syndrome cases have higher URNAP/NAP scores compared to unaffected controls, which suggests that URNAP/NAP is an extremely useful marker for mid-trimester prenatal screening.

Integration of genetics and ultrasonography in prenatal diagnosis: just looking is not enough.

OBJECTIVE: There has been a gradual shift of the focus of prenatal diagnosis from genetics to ultrasonography. We assessed our primary genetics approach to determine what would be missed without the genetics component. STUDY DESIGN: We evaluated referral indications for patients with normal and abnormal prenatal findings from Jan. 1, 1990, to March 31, 1995, and categorized them according to type of fetal anomalies and genetic abnormalities found. Discordance among initial indication, identified risk factors, and observed abnormalities was assessed. RESULTS: The proportion of patients referred for very-high-risk indications increased over time; 13.5% of all patients (1992 of 14,725) had abnormalities. Abnormal outcomes were categorized as 26% chromosomal, 58% ultrasonographic dysmorphologic features, 11% biochemical or deoxyribonucleic acid disorders, 5% infectious, and 11% other. Of the cases of ultrasonographic dysmorphism (exclusive of the aneuploidies), 3.5% were ultimately determined to be syndromic and 2.5% to be discrepant, that is, having a different abnormality than the referred diagnosis. Including the whole spectrum of disorders seen, half of the abnormalities would not be detectable with even high-quality ultrasonography. CONCLUSION: A large number of abnormal findings were not consistent with initial indication for referral. Correct diagnosis depended on increased acuity provided by genetic pedigree analysis and recognition of syndromes. Diligence in the search for associated anomalies, aneuploidy, pedigree analysis, and syndromic abnormalities remain critical components in the differential diagnosis. The elucidation of unexpected findings suggests the advantages of early counseling and a genetics-based approach combined with tertiary rather than primary ultrasonography with counseling only when anomalies are detected.

Parental decisions to terminate/continue following abnormal cytogenetic prenatal diagnosis: "what" is still more important than "when".

This study was undertaken to determine if parental decisions to continue or terminate following the diagnosis of a cytogenetic abnormality have changed over the past 8 years at the same center. Parental decisions in 310 prenatal chromosomal abnormalities were stratified by procedure (chorionic villus sampling [CVS] vs. amniocentesis) and the severity of the anomaly (severe vs mild-moderate). Patients with severe anomalies were much more likely to terminate regardless of gestational age. There was a trend (P = .107) toward a lower rate of termination for mild-moderate degrees in the second trimester. There was no change in patient's decisions over time. Patients' decisions about termination are focused on the severity of the disorder and only marginally influenced by when in gestation the decision is made.

Logistic regression generated probability estimates for trisomy 21 outcomes from serum alpha fetoprotein and beta human chorionic gonadotrophin: simplification with increased specificity.

Traditional Gaussian approaches to biochemical screening make calculations very cumbersome. We have sought to develop a logistic regression mathematical model for the calculation of risk for trisomy 21 in multiple marker screening that would be more "user friendly." Biochemical screening data from 15,444 patients with confirmed normal outcomes and 28 with trisomy 21 were analyzed by logistic regression analysis (LRA) to produce a direct mathematical approach to risk calculation that combines the improvements in sensitivity and specificity already demonstrated by us with extreme value cumulative function surface fittings, but which can be extended for other exploratory variables. LRA yields a 71.4% sensitivity with a 95% specificity which is comparable to our previously published discriminant aneuploidy detection (DADs) approach; both are an improvement over the commonly used Gaussian approach of risk assessment. In our study population, LRA performed as well as DADs; both performed better than the Gaussian method, and LRA is a simpler approach.

Similarity of insulin-dependent diabetics' and non-insulin-dependent diabetics' levels of beta-hCG and unconjugated estriol with controls: no need to adjust as with alpha-fetoprotein.

OBJECTIVE: To determine if the same systematic alteration of serum values seen for alpha-fetoprotein (AFP) in diabetic patients is also seen for beta-hCG and unconjugated estriol (uE3). METHODS: Serum AFP, beta-hCG, and uE3 results were obtained in 18,639 patients for whom complete follow-up information was obtained. Patients were divided into euglycemic (n = 18,088), insulin-requiring diabetics (n = 104), and non-insulin-requiring diabetics (n = 437), as well as by race. RESULTS: The 20% adjustment used for AFP appropriately corrects serum values. No such systematic variation is seen for either beta-hCG or uE3 by glycemic status or race. CONCLUSION: No adjustment for beta-hCG or uE3 is necessary for diabetes for biochemical screening programs.

Multiple marker screening in multifetal gestations: failure to predict adverse pregnancy outcomes.

The objective of the study was to assess whether the association known in singleton pregnancies of high maternal serum alpha-fetoprotein (AFP) or human chorionic gonadotropin (HCG) with adverse outcomes applies also to multifetal gestations. Maternal serum AFP and HCG were evaluated in 207 multifetal pregnancies. High values were defined as a maternal serum AFP of > 4.5 and a HCG of > 4.0 multiples of the median (MoM), with appropriate adjustments. Results were correlated with premature delivery, stillbirths, or pregnancy termination for fetal anomalies. There were 10 stillbirths, 7 terminations of pregnancy for fetal anomalies, and 66 premature deliveries in the study group. Maternal serum AFP was somewhat higher in abnormal pregnancies than in those with normal outcome (3.4 vs. 2.5 MoM, respectively, NS). A high AFP level was found in 6% of pregnancies with adverse outcomes and in 4% of uncomplicated gestations (NS). High HCG values, also observed in 5% of cases, were all associated with normal outcome. Multiple marker screening suggested an increased risk for aneuploidy in 9% of patients, all of whom were euploid on amniocentesis karyotypes. Maternal serum screening in multiple gestations is confounded by the differing contributions of fetuses, and abnormal results cannot reliably predict adverse pregnancy outcomes.

Impact of abnormal second-trimester maternal serum single, double, and triple screening on patient choices about prenatal diagnosis.

The development of multiple-marker biochemical screening has increased the percentage of aneuploidies detected for all age groups and has also increased the abnormality/amniocentesis ratio from about 1 in 85 for maternal serum alpha-fetoprotein alone (single screening) to about 1 in 50 for either maternal serum alpha-fetoprotein plus human chorionic gonadotropin (double screening) or maternal serum alpha-fetoprotein combined with human chorionic gonadotropin and unconjugated estriol (triple screening). We evaluated the decisions to have or decline amniocentesis of 985 patients 'at risk' by either single, double, or triple screening, as multiple markers were phased in over a 3-year period. The patient acceptance of the procedure did not change (approximately 80%) either by actual risk or type of biochemical screening. The labeling of 'at risk' status is more important than actual numerical risks, and the patient perception of risk status must be considered in counseling.

MOMs (multiples of the median) and DADs (discriminant aneuploidy detection): improved specificity and cost-effectiveness of biochemical screening for aneuploidy with DADs.

OBJECTIVE: Our purpose was to assess the efficacy of double- and triple-screening paradigms for Down syndrome and to develop a more logical, statistical approach to risk prediction that will decrease the cost of screening and allow the incorporation of new parameters appropriately weighted for their contribution. STUDY DESIGN: Data from 24,504 patients who had biochemical screening for Down syndrome by single (alpha-fetoprotein), double (alpha-fetoprotein, beta-human chorionic gonadotropin), or triple screening (alpha-fetoprotein, beta-human chorionic gonadotropin, unconjugated estriol) who had complete outcome information were analyzed by (1) existing gaussian-based methods, (2) the Glasgow ratio method, and (3) a new statistical approach (i.e., directly adjusted data sets for discriminant aneuploidy detection [DADs]) RESULTS: By use of individual risk-based thresholds for "at risk" status, both double and triple screening performed far better than single screening, but the percentages of patients at risk varied widely. When the percentages at risk were held constant, the sensitivity of double and triple screenings was similar, suggesting that there are no benefits of using estriol as a third marker. For 25,000 patients the use of only alpha-fetoprotein and beta-human chorionic gonadotropin would save about $500,000, with no decrease in sensitivity. With the DADs approach a statistically sound model giving more stable estimates was developed that permits each factor to be analyzed for its own explained proportion of variance and allows each parameter to have different weighting. For this data set the same sensitivity was seen with, conservatively, a 1% reduction in the percentage of patients at risk, which would reduce by 250 the number of amniocenteses, at a further savings of about $400,000. CONCLUSIONS: By use of existing methods, double screening is equally as effective as triple screening, so that the expense of estriol is unnecessary. The DADs approach, by allowing for variable weighting of parameters, lowers the at risk percentage and will permit a much more flexible approach as new parameters become available. Changing to DADs and eliminating estriol should achieve higher specificity for the same sensitivity and save, conservatively, about $900,000 in this series. Extrapolated nationally, if confirmed, the annual savings could approach $72,000,000.

In utero fetal muscle biopsy alters diagnosis and carrier risks in Duchenne and Becker muscular dystrophy.

OBJECTIVES: We have previously shown that Duchenne muscular dystrophy (DMD) can be diagnosed by fetal muscle biopsy and immunohistochemical staining showing the absence of dystrophin. In Becker muscular dystrophy (BMD), there is a variable dystrophin staining pattern. STUDY DESIGN: A 26-year-old, gravida 5, para 1, SAB 2, VIP 1, white female had a son with the diagnosis of BMD, with no other affected family members. In the current pregnancy, the male fetus inherited the same X chromosome. RESULTS: Fetal muscle biopsy revealed no dystrophin, consistent with the diagnosis of DMD, prompting re-analysis of the sibling whose diagnosis was then changed to DMD. CONCLUSIONS: Molecular techniques in prenatal diagnosis in this case not only led to the diagnosis of a severe disorder in the current pregnancy, but changed the diagnosis in another child, allowing for more appropriate counseling of this couple.

Comparative epidemiology of Down syndrome in two United States population, 1970-1989.

This study compared the epidemiology of Down syndrome over a 20-year period, 1970-1989, in two populations in which livebirths with Down syndrome were believed to be highly ascertained. One population was a 10-county region in southwest Ohio; the second was a five-county region in metropolitan Atlanta, Georgia. The major objectives were to 1) compare observed incidences of Down syndrome over the entire study period; 2) calculate expected incidences of Down syndrome for each population and compare these with observed incidences; 3) determine incidence trends throughout the period; and 4) examine the impact of prenatal diagnosis on the observed incidence of Down syndrome in each population. Excluding aborted fetuses with Down syndrome diagnosed prenatally, the observed incidence of Down syndrome, 0.98, was significantly lower than that expected, 1.27, within the Atlanta white data set. Once the observed data were adjusted to include aborted fetuses with Down syndrome (total incidence = 1.17), no statistically significant differences remained. No differences were found between observed and expected incidences of Down syndrome for whites in southwest Ohio or for other races in either population. Although uncorrected observed incidences were significantly different between the two populations of whites for the entire 20-year period, the differences again disappeared after the data were corrected to include aborted fetuses. No significant effect of prenatal diagnosis on those of other races was found in either population. Expected Down syndrome incidences rose from the late 1970s throughout the 1980s for both racial groups in Ohio and Atlanta, Georgia; however, because the termination of fetuses with Down syndrome increased over the decade, the observed incidence among whites in southwest Ohio remained at earlier levels and actually fell among whites in Atlanta. These results indicate the increasing importance of prenatal diagnosis and selective abortion in the epidemiology of Down syndrome and of correcting for it when comparing incidences between populations, even within the same time period. These data from 2 decades show that differences in both observed and expected incidences of Down syndrome exist between both populations and races, principally because of differences in demographic age structure and maternal age fertility rates and because of differential use of prenatal diagnosis and selective abortion.

Determinants of parental decisions to abort for chromosome abnormalities.

Parental decisions concerning the continuation of pregnancy following prenatal detection of abnormal chromosomes were evaluated for 80 patients whose diagnosis and prenatal counselling were performed in our centre. Twenty-two anomalies were diagnosed by chorionic villus sampling (CVS) and 58 by amniocentesis. The severity of the chromosome anomaly and associated ultrasound findings in the first vs. second trimester were correlated with patients' decisions. No difference was found in the likelihood of parental decisions to interrupt or continue a pregnancy between CVS and amniocentesis for either the 'severe' or the 'questionable' group of chromosome anomalies. Ninety-three per cent of patients with severe prognosis and 27 per cent with questionable prognosis opted for pregnancy termination (p less than 0.0001). The association of ultrasound anomalies and termination was highly significant (p less than 0.001). The severity of the chromosome anomaly, and, to a lesser extent, the visualization of anomalies on ultrasound were the major determinants of parental decisions to terminate the pregnancy. The diagnosis of an anomaly in the first trimester was no more likely ito lead to a termination of pregnancy than in the second trimester.

Counseling for low maternal serum alpha-fetoprotein should emphasize all chromosome anomalies, not just Down syndrome.

In common usage, a low maternal serum alpha-fetoprotein (MSAFP) value is associated with an increased risk of Down syndrome. We have performed amniocenteses for the indication of age-adjusted low MSAFP in 1154 patients and found 13 chromosomally abnormal conceptions. Autosomal trisomies were detected in half the cases. Additional abnormalities included sex-chromosome aberrations, deletions, or triploidy in proportions consistent with those seen in an advanced-maternal-age population. Patients with low serum AFP should be counseled that not only Down syndrome, but other aneuploidies as well, may be diagnosed. The risk quoted should be that of all chromosomal abnormalities, which is about twice the risk calculated for Down syndrome.