Screening For Neural Tube Defects Research Articles

Hereditary persistence of α-fetoprotein: Case report and review of the literature

Persistently elevated alpha-fetoprotein (AFP) levels of 24 to 30 micrograms/ml (normal < 10 micrograms/ml) were found in a 38-year-old healthy man. Subsequently, AFP was found to be elevated in another five out of 13 family members within three generations. The pedigree is consistent with an autosomal dominant inheritance pattern. No discernible disease and no functional abnormality appears to be associated with this clinically benign disorder which has been recorded in the literature on four occasions to date. The reported AFP levels in these other cases ranged from 18 to 198 micrograms/ml. Physiologically, AFP is mainly produced in the liver and the yolk sac of human fetuses more than four weeks old, with peak values of up to 4 mg/ml at 12 to 16 weeks of gestation. After birth, AFP levels usually fall, within eight to 12 months, to a very low concentration of < 10 micrograms/ml and persist at low levels throughout life. However, AFP levels can rise above normal in both children and adults in distinct conditions and diseases which will be discussed. Hereditary persistence of alpha-fetoprotein (HPAFP) should be considered in both children and adults with unexplained and persistent elevation of AFP e.g., those screened for hepatocellular carcinoma or diagnosed for germ cell tumor. It should also be recognized in AFP screening for neural tube defects or Down's syndrome during pregnancy. Hereditary persistence of AFP can be easily confirmed by analyzing AFP levels in family members.

Feto portador de síndrome de turner e tetralogia de fallot associadas à elevação de alfafetoproteína materna

A síndrome de Turner fetal e suas complicações, a hidropisia e o higroma cístico, podem produzir alteração dos marcadores bioquímicos de soro materno inicialmente utilizados no rastreamento de síndrome de Down e de defeitos de tubo neural (DTN). Os autores relatam o caso de uma gestante de 37 anos, que foi rastreada para síndrome de Down e DTN no início do 2º trimestre. Foi constatado aumento da alfafetoproteína de soro materno (MSAFP) e o rastreamento foi considerado positivo para DTN. Foi realizado exame ultra-sonográfico tridimensional, que não demonstrou nenhuma anormalidade fetal ou placentária, caracterizando o caso como elevação idiopática de MSAFP. No 3º trimestre, a gravidez evoluiu com acentuada oligoidrâmnia e alteração do fluxo uteroplacentário, obrigando à instituição de terapia com corticosteróides e parto cesáreo na 34ª semana gestacional. O concepto do sexo feminino foi encaminhado à UTI neonatal, onde foram diagnosticadas tetralogia de Fallot e síndrome de Turner. Esse caso incentivou os autores a rever a literatura sobre marcadores bioquímicos de soro materno na síndrome de Turner e nas malformações cardíacas congênitas. Ao final, propõe-se um protocolo para elevação idiopática de MSAFP.

Screening for Down syndrome at 14 weeks of pregnancy

To investigate whether statistical parameters used in Down syndrome screening between 15 and 22 weeks of pregnancy can be used at 14 weeks, we assayed alpha-fetoprotein (AFP), unconjugated oestriol (uE3), total human chorionic gonadotrophin (hCG), free alpha-hCG, free beta-hCG, and inhibin-A in 16 pregnancies with Down syndrome in the 14th week of pregnancy and expressed values in multiples of the normal median. The median and standard deviation values for these 16 pregnancies were not materially different from those published for 15-22 weeks. It is reasonable, therefore, to offer Down syndrome screening using these markers starting at 14 completed weeks of pregnancy instead of 15 weeks. It needs to be recognized, however, that serum AFP measurement for neural tube defect screening is less effective at this time than between 16 and 18 weeks of pregnancy.

Effect of adjustment of maternal serum ?-fetoprotein levels in insulin-dependent diabetes mellitus

Our objective was to determine the effect of the 20% upward adjustment of maternal serum alphafetoprotein (MSAFP) in patients with insulin-dependent diabetes mellitus (IDDM) on the number of patients that would be classified at increased risk for pregnancy complicated by either Down syndrome (DS) or neural tube defect (NTD). We retrospectively evaluated a database containing 63,110 patients who underwent multiple serum marker screening between 14 and 22 weeks gestation; 620 patients with IDDM had measurements of MSAFP of which 479 also had measurements of beta-HCG, allowing calculation of DS risk. Increased NTD risk was defined as MSAFP >2.5 MOM while increased DS risk was defined as a calculated risk > or =1/270. One IDDM patient delivered an infant with a NTD; it was not detected on serum screening. No infants were born with DS. Of the 620 patients with MSAFP determinations, 9 had values >2.5 MOM before adjustment. After upward adjustment, 7 additional patients were identified. Sixteen patients were identified at increased risk for DS before and after adjustment. Our data suggest that the 20% upward adjustment of MSAFP increases by 78%, the number of patients who would require further evaluation for NTD's. Although we were able to identify 620 women with IDDM who underwent serum screening for NTD, the low prevalence of NTD's did not allow us to demonstrate an increased detection rate. The effect of upward adjustment of MSAFP on the number of patients categorized at increased DS risk appears to be minimal.

Effect of adjustment of maternal serum α‐fetoprotein levels in insulin‐dependent diabetes mellitus

Our objective was to determine the effect of the 20% upward adjustment of maternal serum alphafetoprotein (MSAFP) in patients with insulin-dependent diabetes mellitus (IDDM) on the number of patients that would be classified at increased risk for pregnancy complicated by either Down syndrome (DS) or neural tube defect (NTD). We retrospectively evaluated a database containing 63,110 patients who underwent multiple serum marker screening between 14 and 22 weeks gestation; 620 patients with IDDM had measurements of MSAFP of which 479 also had measurements of β-HCG, allowing calculation of DS risk. Increased NTD risk was defined as MSAFP >2.5 MOM while increased DS risk was defined as a calculated risk ≥1/270. One IDDM patient delivered an infant with a NTD; it was not detected on serum screening. No infants were born with DS. Of the 620 patients with MSAFP determinations, 9 had values >2.5 MOM before adjustment. After upward adjustment, 7 additional patients were identified. Sixteen patients were identified at increased risk for DS before and after adjustment. Our data suggest that the 20% upward adjustment of MSAFP increases by 78%, the number of patients who would require further evaluation for NTD's. Although we were able to identify 620 women with IDDM who underwent serum screening for NTD, the low prevalence of NTD's did not allow us to demonstrate an increased detection rate. The effect of upward adjustment of MSAFP on the number of patients categorized at increased DS risk appears to be minimal. Am. J. Med. Genet. 75:176–178, 1998. © 1998 Wiley-Liss, Inc.

Epidemiology of neural tube defects

Epidemiologic studies have established clear variations in the occurrence of neural tube defects (NTDs) associated with demographic and other factors. Methods of counting NTD-affected pregnancies and other birth defects rely on multiple sources of information such as hospital records and birth certificates. Widespread prenatal diagnosis of NTDs presents special challenges for birth defects monitoring programs. Even before prenatal diagnosis was possible, epidemiologists noted geographic variation in NTD rates; distinctive recurrence patterns within families; variations in NTD rates by race/ethnicity, socioeconomic strata, and sex of the infant or fetus; and changing rates over time. We review highlights of studies of these factors and some conclusions that can be drawn from NTD epidemiologic data. These conclusions include the importance of maternal diet, a finding that has led to preventive interventions, and the suggestion of multiple causes of NTDs, indicating that no single prevention program may prevent the occurrence of all NTDs. We also discuss the relevance of epidemiologic data to NTD screening and counseling policies and the importance of prenatal diagnosis data. Future epidemiologic studies will need to incorporate prenatal records, particularly to study trends. Other emerging themes in epidemiologic research include collaboration between different birth defects monitoring programs, new information from unique geographic areas, new techniques to study gene-environment interactions, and a multidisciplinary emphasis on measuring the effectiveness of prevention programs. MRDD Research Reviews 1998;4:241–246. Published 1998 Wiley-Liss, Inc.

Epidemiology of neural tube defects

Epidemiologic studies have established clear variations in the occurrence of neural tube defects (NTDs) associated with demographic and other factors. Methods of counting NTD-affected pregnancies and other birth defects rely on multiple sources of information such as hospital records and birth certificates. Widespread prenatal diagnosis of NTDs presents special challenges for birth defects monitoring programs. Even before prenatal diagnosis was possible, epidemiologists noted geographic variation in NTD rates; distinctive recurrence patterns within families; variations in NTD rates by race/ethnicity, socioeconomic strata, and sex of the infant or fetus; and changing rates over time. We review highlights of studies of these factors and some conclusions that can be drawn from NTD epidemiologic data. These conclusions include the importance of maternal diet, a finding that has led to preventive interventions, and the suggestion of multiple causes of NTDs, indicating that no single prevention program may prevent the occurrence of all NTDs. We also discuss the relevance of epidemiologic data to NTD screening and counseling policies and the importance of prenatal diagnosis data. Future epidemiologic studies will need to incorporate prenatal records, particularly to study trends. Other emerging themes in epidemiologic research include collaboration between different birth defects monitoring programs, new information from unique geographic areas, new techniques to study gene-environment interactions, and a multidisciplinary emphasis on measuring the effectiveness of prevention programs. MRDD Research Reviews 1998;4:241–246. Published 1998 Wiley-Liss, Inc.

Antepartum screening in the office-based practice: Findings from the Collaborative Ambulatory Research Network

Objective : To examine utilization patterns of four antepartum screening tests by office-based obstetricians. Methods : The population surveyed was the Collaborative Ambulatory Research Network, a voluntary subset of 550 ACOG fellows from 130 practices participating in data collection regarding ambulatory practices. Responses from self-administered questionnaires concerning screening for hepatitis B, gestational diabetes, neural tube defects, and trisomy 21 were analyzed. Results : Hepatitis screening was performed by all practices with 95% (2750 of 2886) of women tested; however, only 55% (six of 11) of at-risk newborns received treatment. For gestational diabetes screening, 94% (116 of 124) administer a 50-g glucose load to all parturients, regardless of risk factors, two-thirds initiate further testing for a 1-hour post-load glucose of 140 mg/dL or greater, and 34% do so at lower glucose levels (130–135 mg/dL). For neural tube defect screening, 92% (95 of 103) offer maternal serum alphafetoprotein (MSAFP) screening although when results are elevated, further recommendations are varied. For women under 35 years of age, 84% (87 of 103) offer serum screening for trisomy 21 risk, most (68%) with double or triple (MSAFP, hCG, and estriol) markers. For women over 35 years, a majority (87%) offer serum screening, although half do so only if amniocentesis is declined for age risk alone. The relatively high initial positive rate and poor specificity of serum screening were underappreciated by a large number of respondents. Conclusion : Increased initial and continuing education of antenatal care providers is warranted if these screening tools are to perform optimally within office practices.

Nonparametric Density Estimation and Discrimination from Images of Shapes

SUMMARY Nonparametric density estimation is the basis for a new methodology for discrimination using shape data in the form of pixel images. Our work is driven by an application based on screening for neural tube defects from ultrasonography data that comprise binary pixel images of head shapes from human fetuses. We discuss the choice of smoothing parameters used for the density estimates, the variation that is inherent in our method and how our approach could be extended to take into account other discriminatory information. We compare our method based on density estimates with alternative approaches such as those based on Fourier descriptors.

Down Syndrome and Neural Tube Defect Screening: The Value of Using Gestational Age by Ultrasonography

Down Syndrome and Neural Tube Defect Screening: The Value of Using Gestational Age by Ultrasonography

Serum triple-marker screening in in vitro fertilization and naturally conceived pregnancies

To determine whether results of second-trimester maternal serum triple-marker screening for Down syndrome and open neural tube defects in singleton pregnancies conceived from in vitro fertilization (IVF) differ from those of pregnancies conceived spontaneously. The screen-positive rates and triple-marker levels of patients conceiving singleton pregnancies by IVF were compared to age-adjusted standards. Sixty-nine singleton IVF pregnancies with maternal serum screening were identified. Twenty-one (30.4%) of the 69 IVF singleton pregnancies had a positive screen for Down syndrome compared with a 14.4% expected screen-positive rate for the maternal age distribution in our observed sample (P = .013). The screen-positive rate for open neural tube defects in the measured population was similar to anticipated values based on historic controls (5.8% in IVF patients versus 5.3% in the total population). The median levels of the triple markers were 0.95 multiples of the median (MoM) for alpha-fetoprotein (AFP), 0.90 MoM for unconjugated estriol (E3), and 1.22 MoM for hCG. The increased hCG levels as well as the slightly lower AFP and unconjugated E3 levels may contribute to the higher Down syndrome screen-positive rate in this IVF singleton population. These results may be due to the number of embryos transferred, the maternal hormonal environment of the IVF process, or other factors. Pregnancies conceived by IVF may be twice as likely to have a positive maternal serum screening test. As additional data are collected, corrected standards should be determined.

Down syndrome and neural tube defect screening: The value of using gestational age by ultrasonography

OBJECTIVE: Our goal was to determine whether gestational age should be based on ultrasonographic evaluation or last menstrual period data in the interpretation of second-trimester maternal serum screening for Down syndrome and open neural tube defects. STUDY DESIGN: Initial and revised screen-positive rates and detection rates were reviewed for women undergoing triple-marker testing (maternal serum α-fetoprotein, human chorionic gonadotropin, and unconjugated estriol). The study population consisted of >24,000 women at 15.0 to 21.9 weeks' gestation with approximately 60% of test interpretations based on ultrasonographic evaluation of gestational age. Gestational age and screening results were compared for 24 Down syndrome pregnancies in which both ultrasonography and last menstrual period dating were available. RESULTS: Both initial and revised screen-positive rates for Down syndrome were significantly lower when ultrasonographic data were used compared with last menstrual period dating. The detection rate for Down syndrome appeared to be higher with ultrasonographic dating (approximately 76% vs 60% for last menstrual period dating). Down syndrome fetuses had a significantly shorter gestational age when evaluated by ultrasonography (relative to last menstrual period dating), but a similar trend was also seen in control pregnancies. Initial and revised screen-positive rates for open neural tube defects were higher for women who had received an ultrasonographic examination compared with the rates for those women referred with only last menstrual period data. The detection rates for open neural tube defects were similar for both methods of pregnancy dating. CONCLUSION: By use of ultrasonographic measurement of gestational age, the number of amniocenteses performed to detect Down syndrome can be substantially reduced while detection rates are maintained or improved. (Am J Obstet Gynecol 1997;176:1056-61.)

Antecedent circumstances surrounding neural tube defect births in 1990-1991. The Steering Committee of the National Confidential Enquiry into Counselling for Genetic Disorders.

To investigate births with neural tube defects at a time when most districts were screening for the condition. The objective was to document the circumstances surrounding each affected birth and assess the care provided against given standards. Retrospective review of antenatal casenotes by the obstetric team. Three hundred and eight births in England and Wales in 1990 to 1991 were reported to the Office of Population Census Survey (OPCS) to involve neural tube defects. Sufficient information was available to identify both the woman and the obstetrician in 213 pregnancies. Details were obtained from a questionnaire completed by the obstetric team for 168 (79%). In 20/168 cases either the reported outcome was not a live birth/stillbirth or the pregnancy did not involve a neural tube defect: eight resulted in a 'normal' infant, eight were terminated and in four the abnormality was not a neural tube defect. Thus 148 eligible cases were available for analysis. Of the 148 births, the anomaly was not detected prenatally or detected later than 25 weeks of gestation in 98 cases (66%), diagnosed in a multiple pregnancy in 24 (16%) and diagnosed prenatally but the woman chose to continue the pregnancy in 26 (18%). Of the 98 births not detected prenatally or detected late during pregnancy, the surrounding circumstances were that screening was declined in six cases (4%), screening was not offered due to late booking in 30 (20%), serum alpha-fetoprotein screening gave a false negative result in eight (5%), ultrasound screening gave a false negative result in 29 (20%), both screening methods gave false negative results in 17 (11%) and other reasons in eight (5%). The estimated sensitivity of ultrasound screening for anencephaly was 100%. For spina bifida the estimated sensitivity for singleton pregnancies is higher for serum alpha-fetoprotein screening, 84% to 92%, than ultrasound screening, 70% to 84%, for a range of assumptions regarding the degree of under-reporting to OPCS of live births and terminations. Late booking precluded the offer of screening tests in a substantial proportion (22%) of cases. The presence of multiple fetuses including one or more with a neural tube defect was a serious additional complication in prenatal screening, diagnosis and counselling. Screening for neural tube defects was widespread in 1990 to 1991, although variations in the services provided were documented. Ultrasound scanning was a major component but was associated with a lower sensitivity than maternal serum alpha-fetoprotein screening for neural tube defects other than anencephaly.

Refinements in managing maternal weight adjustment for interpreting prenatal screening results.

This study examines the relationship between maternal weight and serum levels of alpha-fetoprotein, unconjugated oestriol, and human chorionic gonadotropin in a population of 47,585 women being provided with prenatal screening for Down's syndrome and open neural tube defects. The study population contains sufficient numbers of women at the extremes of weight to allow the determination that a reciprocal-linear equation more accurately describes the weight relationship for two of the three analytes than the currently used log-linear equations. The reciprocal-linear equations, while more appropriate, provide only a minimal advantage over the log-linear equations. A more important finding is that published weight equations may not be optimal for some screening programmes, due to differences in the mean weight of the populations being tested. Screening programmes are encouraged to calculate their own weight correction formulae, based on data from their own population, and to monitor the mean maternal weight to detect when modifications in the weight correction formulae might be indicated.

Quality assessment of a prenatal screening program

Epidemiologic monitoring is a process which uses data generated from the screened population as a quality control measure. Most commonly, laboratories monitor the percentage of women with screen positive test results, i.e., with test results falling at or above a specified multiple of the median (MoM) for open neural tube defect screening or, with a risk at or above a specified risk cut-off for Down's syndrome screening. These percentages are sensitive to inaccurate and imprecise assays, inappropriate reference data, and long term assay drift. In fetal Down's syndrome screening it is necessary to simultaneously monitor two or more assays, which is accomplished by monitoring the median MoM for each assay (which should be 1.0 within statistical limits) calculated using patient MoM values. Monitoring the median MoM can identify inappropriate adjustment factors for variables which affect the MoM such as maternal weight. Epidemiologic monitoring is a useful tool for identifying problems which are not readily apparent using traditional quality control measures.

Insulin-dependent diabetes mellitus and prenatal screening results: current experience from a regional screening programme.

From around 91,000 women having routine prenatal screening for Down's syndrome and neural tube defects between July 1992 and October 1995, 261 women were identified as having insulin-dependent diabetes mellitus (IDDM). Alpha-fetoprotein (AFP) and human chorionic gonadotrophin (hCG) levels were reduced in these women, with median levels of 0.89 and 0.91 multiples of the median (MOM), respectively. The IDDM patients had a median weight which was 6 kg heavier than that of non-IDDM women. After correction for maternal weight, the AFP and hCG levels in the IDDM patients were 0.98 and 0.92 MOM, respectively. In routine practice, using results which were not weight-corrected, the IDDM women were neither over- nor under-represented in the high-risk group for Down's syndrome, but showed a tendency to be under-represented in the high-risk group for neural tube defects.

Antepartum screening in the office-based practice: Findings from the collaborative ambulatory research network

To examine utilization patterns of four antepartum screening tests by office-based obstetricians. The population surveyed was the Collaborative Ambulatory Research Network, a voluntary subset of 550 ACOG fellows from 130 practices participating in data collection regarding ambulatory practices. Responses from self-administered questionnaires concerning screening for hepatitis B, gestational diabetes, neural tube defects, and trisomy 21 were analyzed. Hepatitis screening was performed by all practices with 95% (2750 of 2886) of women tested; however, only 55% (six of 11) of at-risk newborns received treatment. For gestational diabetes screening, 94% (116 of 124) administer a 50-g glucose load to all parturients, regardless of risk factors, two-thirds initiate further testing for a 1-hour post-load glucose of 140 mg/dL or greater, and 34% do so at lower glucose levels (130-135 mg/dL). For neural tube defect screening, 92% (95 of 103) offer maternal serum alpha-fetoprotein (MSAFP) screening although when results are elevated, further recommendations are varied. For women under 35 years of age, 84% (87 of 103) offer serum screening for trisomy 21 risk, most (68%) with double or triple (MSAFP, hCG, and estriol) markers. For women over 35 years, a majority (87%) offer serum screening, although half do so only if amniocentesis is declined for age risk alone. The relatively high initial positive rate and poor specificity of serum screening were underappreciated by a large number of respondents. Increased initial and continuing education of antenatal care providers is warranted if these screening tools are to perform optimally within office practices.

Effect of allowing for ethnic group in prenatal screening for Down's syndrome.

We conducted a study to investigate ethnic group differences in levels of serum markers used in screening for Down's syndrome [serum alpha-fetoprotein (AFP), unconjugated oestriol (uE3), total human chorionic gonadotrophin (hCG), free alpha- and free beta-hCG, and dimeric inhibin-A], to estimate the extent to which maternal weight differences between ethnic groups explain these differences, and to estimate the effect of adjusting for ethnic group and maternal weight on screening performance. Serum measurements were taken from women who were screened prenatally for Down's syndrome. AFP, uE3, and hCG concentrations were available from 9462 white, 4215 black, and 4392 South Asian women with singleton pregnancies without Down's syndrome or neural tube defects between 15 and 22 weeks' gestational age. Frozen serum samples were available from a subset of 922 white, 449 black, and 135 South Asian women and were used for measurement of free alpha-hCG, free beta-hCG, and inhibin. Values were expressed as multiples of the median (MOM) for women of the same gestational age. There were statistically significant differences in the serum marker levels between ethnic groups that were not explained by differences in maternal weight. The main differences were found in black women compared with white women; black women had serum AFP levels 22 per cent higher (95 per cent confidence interval 20-24 per cent), total hCG levels 19 per cent higher (16-22 per cent), and free beta-hCG levels 12 per cent (3-21 per cent) higher. The other differences were less than 10 per cent. Adjusting for ethnic group only had a small estimated effect on screening performance: a maximum of about 0.5 per cent extra detection at a 5 per cent false-positive rate. At a fixed risk cut-off level, the false-positive rate will not be materially different between different ethnic groups. Adjusting serum markers for ethnic groups improves Down's syndrome screening performance to a very small extent. It is worthwhile because of its established value in AFP screening for open neural tube defects.

Periconceptional folate intake and neural tube defects.

Approximately 50% of neural tube defects may be folate-preventable and perhaps even more in other countries where prevalence is high. The Public Health Service has issued the recommendation that all women of childbearing age in the United States who are capable of becoming pregnant should consume 400 micrograms of folic acid/day for the purpose of reducing this risk. Ways in which a reproductive age woman could achieve this goal include: 1) fortifying a food sample with folic acid, 2) consuming supplements containing at least 400 mcg of folic acid, or 3) increasing nutrient intake by eating foods rich in folate. Advantages of consuming foods high in folate content are that it is a natural behavior and consistent with other dietary recommendations. However, this method is dependent upon a proper diet, and equivalencies of conjugated (dietary form) vs. unconjugated (in supplements) folate are unknown. The benefit of a supplementation policy is that the appropriate group can be targeted as pregnancies are planned, whereas primary limitations to taking a supplement would be compliance and most cases in need would not be reached. The advantage of fortification is that it is likely to reach everyone before conception, while the major disadvantage is that nontargeted populations will also receive more folic acid. Adequate consumption of folic acid should begin before and continue during at least the first 4 weeks after conception when the fetal neural tube is being formed. Standard methods of screening for neural tube defects should continue during pregnancy. The risk of a recurrent neural tube defect is 2-3%, and a higher periconception daily intake of folic acid (4 mg per day) is recommended.

Prenatal maternal dried blood screening with α-fetoprotein and free β-human chorionic gonadotropin for open neural tube defect and Down syndrome

OBJECTIVE: Our purpose was to evaluate second-trimester prenatal screening for open neural tube defects and Down syndrome by use of dried blood specimen collection and transport. STUDY DESIGN: A prospective study of 7497 dried blood specimens from patients <35 years old was performed. Specimens were assayed for maternal blood α-fetoprotein and free β-human chorionic gonadotropin. Patient-specific risks for both disorders were calculated and used to determine whether further evaluation was indicated. The study included an evaluation of the median and SD of analyte multiple of the median levels. RESULTS: The initial positive rate for open neural tube defect was 4.4% adjusted to 2.7% after ultrasonographic revision and collection of a second sample. The initial positive rate for Down syndrome was 3.6%, adjusted to 2.8% after ultrasonographic revision. All seven cases of open neural tube defect were detected within the increased risk group. Six of 8 (75%) cases of Down syndrome were detected. The median α-fetoprotein multiple of the median was 3.5 in open neural tube defect cases and 0.6 in Down syndrome cases. The median free β-human chorionic gonadotropin multiple of the median was 2.4 in Down syndrome cases. The SD (log e ) of α-fetoprotein and free β-human chorionic gonadotropin in 5868 unaffected white patients was 0.4022 and 0.5635, respectively. CONCLUSION: Second-trimester dried blood screening for open neural tube defects and Down syndrome can achieve screening efficiency comparable to serum-based protocols with distinct advantages over the conventional method of blood collection. (A M J O BSTET G YNECOL 1996;174:566-72.)