Prenatal serum alpha-fetoprotein screening for neural tube defects.

Twenty-two cases of open neural tube defect were found in a population of 17,703 unselected pregnancies (1.2 per 1000) within the Long Island, New York, region. Voluntary screening of maternal serum alpha-fetoprotein levels identified 20 of the 22 cases (91%). Six hundred ninety-two participants demonstrated serial elevations in maternal serum alpha-fetoprotein. Of this group, which was designated at increased risk for open neural tube defect, 24% had underestimated gestational age, 13% had multiple gestations, and 53% were candidates for amniocentesis. In the amniocentesis group, the detection yield of neural tube defect was 20 per 365 (5.5%). Neither false-negative amniotic fluid evaluations nor termination of normal pregnancy due to false-positive amniotic fluid levels occurred. Perinatal outcome data, including pregnancy complications, date, mode of delivery, sex, birth weight, Apgar score, and congenital malformations of the neonate other than neural tube defect, are reported for the first 9300 consecutive participants of the 17,703 population study. These data identify a correlation between rate of perinatal loss and maternal serum alpha-fetoprotein levels.

Amniography in the prenatal diagnosis of neural tube defects.

Amniography for the visualization and confirmation of suspected neural tube defect was performed in 9 midtrimester gravidas. In all cases, amniotic fluid alpha-feto protein (AFP) was abnormally elevated. Four cases of anencephaly and one of spina bifida were demonstrated by amniography. These pregnancies were terminated and the defects were confirmed by gross pathologic examination. In 4 remaining cases, amniography was normal. Three of these pregnancies proceeded to term, culminating in the birth of a normal child. The fourth patient had spontaneous abortion of a normal fetus at 23 weeks of gestation. The experience reported here suggests that amniography is an important adjunctive diagnostic technique in the prenatal diagnosis of neural tube defect, and if used correctly, may significantly reduce the chance of false-positive diagnosis.

Maternal serum and amniotic fluid alpha-fetoprotein as a marker of acute fetal distress in a midtrimester abortion model.

Maternal serum (MS) and amniotic fluid (AF) alpha-fetoprotein (alpha-FP) levels were serially determined in 18 cases of elective midtrimester abortion. Prostaglandin F2alpha (PGF2alpha) and 20% NaCl were used as the abortifacients in 2 groups of 9 patients, respectively. The time from instillation to abortion (IAT) was accurately recorded in all cases. A marked 260-600% increase in MS alpha-FP occurred prior to fetal demise in both groups. Amniotic fluid alpha-FP content remained largely unchanged for the first 6 hours following intraamniotic prostaglandin injection. A 50% INCREASE WAS OBSERVED IN THE AF alpha-FP content in the group with 20% NaCl-induced abortion (after an initial dilutionary drop). The results of this investigation confirm the value of alpha-FP in MS as a marker of impending fetal demise. This rise is not caused by a prior alpha-FP change in the AF. The data suggest a major fetomaternal transplacental route for alpha-FP.

Origin of amniotic fluid alpha-fetoprotein in normal and defective pregnancies.

Alpha-fetoprotein was determined by electroimmunodiffusion and radioimmunoassay in 109 neonatal urine samples and 94 amniotic fluid samples. The samples were obtained from newborns and from pregnancies ranging in gestational age from 20 to 40 weeks. When alpha-fetoprotein values of neonatal urine and amniotic fluid were correspondingly correlated with gestational age, almost identical declining curves could be drawn. Twenty-one cerebrospinal fluid samples from newborns ranging from 25 to 40 weeks of gestation were similarly determined. No correlation between cerebrospinal fluid alpha-fetoprotein and gestational age could be demonstrated. It is concluded that fetal urine is the major source of alpha-fetoprotein in the amniotic fluid of normal pregnancy. In pregnancies associated with neural tube defects, alpha-fetoprotein elevation is probably not due to the leakage of cerebrospinal fluid into the amniotic cavity.

Rapid assay--possible application in the diagnosis of premature rupture of the membranes.

Premature rupture of the membranes frequently presents a diagnostic dilemma to the clinician. The presence of alpha-fetoprotein (AFP) in amniotic fluid suggests a possible solution. A rapid, easy-to-use latex agglutination test for AFP was evaluated on 99 amniotic fluid samples of known AFP concentration. Body fluids (maternal serum, urine, vaginal secretions, and seminal fluid) that commonly interfere with other tests were also studied. The sensitivity for amniotic fluids from gestations less than 39 weeks was 93%, and specificity was 94%. The test is most accurate under 35 weeks, when diagnosis is critical. Equivocal results may be resolved by using radioimmunoassay. The results suggest that a rapid assay for AFP may be useful in the diagnosis of ruptured membranes. It has few interfering factors, is safe, and requires no elaborate equipment or training.

First-trimester Down syndrome screening using dried blood biochemistry and nuchal translucency.

OBJECTIVE: To assess the effectiveness of free beta-hCG, pregnancy-associated plasma protein A, and nuchal translucency in a prospective first-trimester prenatal screening study for Down syndrome and trisomy 18. METHODS: Risks were calculated for Down syndrome and trisomy 18 based on maternal age and biochemistry only (n = 10,251), nuchal translucency only (n = 5809), and the combination of nuchal translucency and biochemistry (n = 5809). RESULTS: The study population included 50 Down syndrome and 20 trisomy 18 cases. Nuchal translucency measurement was done on 33 Down syndrome and 13 trisomy 18 cases. Down syndrome screening using combined biochemistry and ultrasound resulted in a false-positive rate of 4.5% (95% confidence interval [CI] 3.9%, 5.2%) and detection rate of 87.5% (95% CI 47%, 100%) in patients under age 35 years. In older patients, the false-positive rate was 14.3% (95% CI 12.7%, 15. 8%) and detection rate was 92% (95% CI 74%, 99%). For trisomy 18 screening, the false-positive rate was 0.4% (95% CI 0.24%, 0.69%) and detection rate was 100% (95% CI 40%, 100%) in younger patients, whereas in older patients the false-positive rate was 1.4% (95% CI 0. 9%, 2.0%) and detection rate was 100% (95% CI 66%, 100%). Using modeling, at a fixed 5% false-positive rate, the Down syndrome detection rate was 91%. Conversely, at a fixed 70% Down syndrome detection rate, the false-positive rate was 1.4%. CONCLUSION: First-trimester screening for Down syndrome and trisomy 18 is effective and offers substantial benefits to clinicians and patients.

Amniotic fluid adenosine 3',5' - monophosphate in prostaglandin-induced midtrimester abortions.

Cyclic adenosine 3'5-monophosphate (cAMP) was serially measured in the amniotic fluid (AF) of 9 patients undergoing midtrimester abortions induced by intraamniotic prostaglandins. The results demonstrate an increase in AF cAMP ranging from 2- to 7-fold within the 6 hours of observation. The fetal heart tones were closely monitored by a Doppler instrument and the time from injection of abortifacient to fetal demise (IDT) and to fetal expulsion (IAT) was accurately recorded. No correlation between the rate of AF cAMP increase and IDT or IAT could be demonstrated. The concentration of cAMP in amniotic fluid obtained from patients with fetal demise in utero was lower than that found in AF of fetuses of corresponding gestational age where the fetus was alive. The significance of AF cAMP as a potential indicator of fetal distress is discussed.

Amniotic fluid alpha-fetoprotein as a marker in prenatal diagnosis of neural tube defects.

The prenatal diagnosis of anencephaly and spina bifida (neural tube defect, NTD) through amniotic fluid analysis for alpha-fetoprotein (AFP) is gradually gaining clinical recognition. AFP concentrations were determined in 237 amniotic fluids from normal pregnancies ranging between 7 and 42 weeks of gestation. A steady decline in AFP from 26 mug/ml at 7-9 weeks to 155 ng/ml at term is observed. AFP concentration was determined in 35 amniotic fluids from 33 confirmed neural tube defective pregnancies. In 14 cases where amniotic fluid was examined prior to the 26th week of gestation. AFP was markedly elevated when compared with the normal range of the same gestational period. In 21 amniotic fluids past the 26th week, 17 cases (85-) had markedly elevated AFP levels; however, 2 cases of anencephaly, 1 of spina bifida, and 1 of hydrocephaly gave levels within the normal range. It is concluded that elevated AFP in the amniotic fluid is a reliable but nonspecific marker for open neural tube defects prior to the 26th week of pregnancy, but may become normal after the 26th week in a small percentage of patients.

PIP: A steady decline in alpha fetoprotein (AFP) levels was observed in single specimens of amniotic fluid (AF) from 237 patients, ranging from 26 mcg/ml at 7-9 weeks to 155 ng/ml at term. All pregnancies tested were normal. 35 AF specimens from 33 confirmed neural tube defective pregnancies were assayed for AFP. Very high levels of AFP were found in 13/14 fluids examined before Week 26 of gestation. A value of 23 mcg/ml was determined in 1 sample where the infant had skin-covered encephalocele. A fluid taken from the same patient at 34 weeks fell to 6.4 mcg of AFP. 21 AF samples from patients past the 26th week of pregnancy were analyzed. Of these, 1 case of spina bifida and 2 of anecephaly gave no detectable levels of AFP by electroimmunodiffusion. By radioimmunoassay, however, these samples measured 3700, 256, and 700 ng/ml. 1 case of hydroencephaly, examined at 33 weeks, had an AFP level of 1.5 mcg/ml. A sharp drop in AFP from 353.6 at 15 weeks to 10.4 mcg/ml at 29 weeks was noted in the only serially examined open neural tube defective pregnancy.

Early prenatal diagnosis of soft-tissue malformations.

This study presents 3 cases of severe soft-tissue malformations of the fetus. Prenatal diagnosis was established early in the second trimester, and the accuracy of the diagnosis was confirmed by pathological examination in each instance. A clinically oriented work-up plan for early prenatal diagnosis is proposed.

Dual Analyte immunoassay--a new approach to neural tube defect and Down's syndrome screening.

A microtiter plate based Dual Analyte enzyme-immunoassay method for the simultaneous measurement of alpha-fetoprotein (AFP) and Free-beta human chorionic gonadotrophin (hCG) was evaluated. This rapid assay, which has application in both Neural Tube Defect screening and Down's screening, shows good precision with between assay coefficients of variation between 5 and 7.5% for AFP and 3.7 to 5.8% for Free-beta(hCG). Correlation with single analyte procedures is good, with correlation coefficients being greater than 0.91 in both cases. Clinical discrimination in detecting both types of abnormalities is not compromised by this new simultaneous Dual Analyte assay. We conclude that the Dual Analyte approach, which combines analytes achieving the highest known detection efficiency, will bring about improvements in the efficiency of screening, reduce costs and improve report turnaround, all leading to better quality of patient care.

Free beta-chorionic gonadotropin: a cross-reactivity study of two immunometric assays used in prenatal maternal serum screening for Down's syndrome.

We have evaluated the cross-reactivity characteristics of two distinct immunometric assays for the measurement of free beta-human chorionic gonadotropin (free beta). These maternal serum assays have been used in the initial studies which evaluated free beta as a marker in the prenatal detection of Down's syndrome. It has been suggested that free beta assays are subject to substantial potential for cross-reactivity. To confirm that free beta was the analyte responsible for enhanced detection efficiency both non-competitive and competitive cross-reactivity evaluations were undertaken. These studies demonstrated acceptably small cross-reactivity to other glycoprotein hormones or their beta components. We conclude that properly designed free beta assays will provide specific analyte measurement and improved detection efficiency in Down's syndrome screening.

First trimester biochemical screening for trisomy 21: the role of free beta hCG, alpha fetoprotein and pregnancy associated plasma protein A.

The potential efficacy of screening for trisomy 21 in the first trimester, using maternal serum markers alpha fetoprotein, free beta human chorionic gonadotropin, unconjugated oestriol and pregnancy associated plasma protein A, was studied in an unselected population of women between the seventh and fourteenth week of gestation. Using a combination of alpha fetoprotein and free beta human chorionic gonadotropin, 53% of affected pregnancies could be identified at a false positive rate of 5%. Unconjugated oestriol and pregnancy associated plasma protein A levels were lower in cases of trisomy 21, but their inclusion with other markers did not significantly improve detection rate. Monitoring the same pregnancies also in the second trimester showed that screening in the first trimester identified the same cases as in the second. We conclude that first trimester screening using free beta human chorionic gonadotropin and alpha fetoprotein, is a viable possibility and will lead to detection rates in excess of 50%. Prospective studies are needed to confirm these observations.

Dual analyte immunoassay in neural tube defect and Down's syndrome screening: results of a multicentre clinical trial.

We report a multicentre clinical field trial of a novel dual analyte enzyme immunoassay method for the simultaneous measurement of alpha-fetoprotein (AFP) and free beta-human choriogonadotropin (hCG) in the same microtitre well. The assay was shown to have good technical performance in the hands of all trial centres, with between assay coefficients of variation better than 10% for both analyte across the whole of the assay ranges. The method compared well with single analyte measuring procedures and produced acceptable performance as judged by external quality assurance criteria. Recovery of added analyte and analyte dilution curves also showed acceptable performance. In clinical evaluation of a large set of neural tube defect cases, good clinical discrimination from unaffected cases was observed using AFP. With over 150 Down's syndrome cases, the combination of AFP and free beta hCG confirmed the high detection rates achievable using this marker combination, with detection rates in excess of 70% in early gestation. We conclude that the combination of clinically superior markers coupled with technologically innovative assay design will lead to more efficient Down's screening programmes.

Prenatal screening for trisomy 18 with free beta human chorionic gonadotrophin as a marker.

OBJECTIVE: To determine the relation between maternal serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations in pregnancies complicated by trisomy 18 and establish whether prenatal biochemical screening for this condition could be developed in a way similar to that proposed for trisomy 21. DESIGN: Serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations in women with singleton pregnancies affected by cytogenetically confirmed trisomy 18, uncomplicated by neural tube defect or ventral wall defect, were identified from prospective trisomy 21 screening programmes. Additionally, stored maternal serum from similar pregnancies was analysed retrospectively. Analyte concentrations from singleton unaffected pregnancies were identified from a prospective screening programme as controls. Statistical parameters of the affected and unaffected populations were compiled. SETTING: Biochemical screening laboratories in Britain and the United States. SUBJECTS: 52 women with singleton pregnancies complicated by trisomy 18; control population of 6661 women with unaffected singleton pregnancies. MAIN OUTCOME MEASURES: Median values of each analyte and their distribution in the affected and unaffected populations; detection rate of trisomy 18 and the false positive rate. RESULTS: Maternal serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations were significantly lower in pregnancies complicated by trisomy 18 (median values 0.71 and 0.37 respectively). By using a multivariate risk algorithm incorporating maternal age risk of trisomy 18 and the concentration of the two biochemical markers it was predicted that 50% of trisomy 18 cases (unaffected by neural tube defect or ventral wall defect) could be detected with a 1% false positive rate. CONCLUSION: Second trimester biochemical screening for trisomy 18 could be a valuable addition to trisomy 21 screening programmes.