Amniography and the false-positive amniotic-fluid A.F.P.
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Biomedical subjects
Publications and source records attributed to J N Macri.
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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.
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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.
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A prospective program for the prenatal detection of neural tube defects in a high-risk pregnancy group has been under way for one year. Twenty high-risk mothers have undergone a complete prenatal work-up, including sonography, amniocentesis, and amniotic fluid and maternal serum alpha-fetoprotein quantitation. Within this group, two cases were prospectively diagnosed and were later confirmed.
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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.
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.
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.
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The prenatal diagnosis of neural tube defects is now possible in about 90 per cent of cases by assaying the amniotic fluid for alpha fetoprotein. The accuracy of beta-trace protein assays on amniotic fluid samples from defective fetuses was compared to alpha-fetoprotein studies. At present, alpha-fetoprotein studies provide more reliable results.
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