Second trimester levels of maternal serum inhibin A in pregnancies affected by fetal neural tube defects

Inhibin A is effective as a second trimester maternal serum marker for Down syndrome screening. In the present study, inhibin A levels were measured in second trimester maternal serum samples from 28 pregnancies affected with open neural tube defects; 12 associated with open spina bifida and 16 associated with anencephaly. Each measurement was expressed as a multiple of the median (MoM) for control singleton pregnancies (n=1464) of the same completed week of gestation. Inhibin A levels were not significantly altered in cases of open neural tube defects; the median value was 0.96 MoM in cases of open spina bifida and 1.19 MoM in cases of anencephaly. Therefore, second trimester maternal serum inhibin A levels will not have an impact on prenatal detection of open neural tube defects.     

Maternal serum alpha-fetoprotein screening for open neural tube defects in twin pregnancies.

Data on maternal serum alpha-fetoprotein (AFP) levels at 13-24 weeks' gestation in 46 twin pregnancies with open neural tube defects (22 with anencephaly, 24 with open spina bifida) and 169 unaffected twins were used to estimate the detection and false-positive rates associated with different cut-off levels. Using the conventional cut-off level of 2.5 multiples of the median (MoM) for unaffected singleton pregnancies of the same gestation and laboratory, the detection rate in twins was 99 per cent for anencephaly and 89 per cent for open spina bifida, with a false-positive rate of 30 per cent. Using a 5.0 MoM cut-off level to maintain a similar false-positive rate to that found among singleton pregnancies at 16-18 weeks' gestation (about 3 per cent), the detection rate was 83 per cent for anencephaly and 39 per cent for open spina bifida. Estimates are provided of the odds of having an affected twin pregnancy given a positive AFP result as well as the odds for individual women with a raised AFP level.     

Ratio of immunochemically determined amniotic fluid acetylcholinesterase to butyrylcholinesterase in the differential diagnosis of fetal abnormalities.

A total of 111 amniotic fluid samples, clear or blood stained, with elevated levels of alpha-fetoprotein and acetylcholinesterase was analysed by immunoassays specific for acetylcholinesterase and butyrylcholinesterase and the acetylcholinesterase/butyrylcholinesterase-ratios determined. Samples from 40 pregnancies associated with anencephaly, 47 pregnancies associated with open spina bifida or encephalocele and six pregnancies with fetal intrauterine death or miscarriage all had ratios of greater than 0.14. All 11 pregnancies with fetal ventral wall defects had ratios less than 0.14 as had four pregnancies with normal outcome and elevated levels of alpha-fetoprotein and acetylcholinesterase. Three fetuses with both open spina bifida and ventral wall defects were associated with ratios above 0.14. These results suggest that immunochemical determination of acetylcholinesterase and butyrylcholinesterase can be used to distinguish pregnancies complicated by anencephaly, open spina bifida, encephalocele and miscarriage from those with ventral wall defects and samples with false positive elevated levels of alpha-fetoprotein and acetylcholinesterase. The procedure is accurate and simple to carry out and well suited to routine use in a clinical chemistry laboratory.     

Maternal serum alpha-fetoprotein in fetal neural tube and abdominal wall defects at 10 to 14 weeks of gestation

Maternal serum alpha-fetoprotein concentration was determined in nine pregnancies with fetal anencephaly, seven with exomphalos containing liver, two with spina bifida and 100 normal controls at 10 to 14 weeks of gestation. The median alpha-fetoprotein in the group with fetal anencephaly and exomphalos was significantly higher than in normal fetuses but the sensitivity of this test is likely to be only about 30% for a false positive rate of 5%.     

The impact of maternal serum alpha fetoprotein screening on open neural tube defect births in north-east Scotland

Over the three years period 1980-1982, 18 256 pregnancies in the Grampian Region of N-E Scotland including the islands of Orkney and Shetland were screened for raised levels of maternal serum alpha fetoprotein (MSAFP) in the second trimester. Thirty six cases of fetal open neural tube defect in singletons were detected (18 anencephaly and 18 spina bifida). Four additional cases of open spina bifida were associated with normal MSAFP levels although two of these were detected by amniotic fluid AFP measurement when amniocentesis was carried out because of previous NTD history. A further three cases of open spina bifida and two of anencephaly occurred in unscreened pregnancies. The MSAFP screening programme alone was thus instrumental in reducing the birth incidence of open neural tube defects by 36 out of 45 cases (80 per cent) in singletons.     

Second-trimester maternal serum analyte levels associated with fetal trisomy 13.

The aim of this study was to determine whether pregnancies affected by fetal trisomy 13 are associated with second-trimester maternal serum analyte levels different from those typical of the unaffected population. Pregnancies with trisomy 13 were identified through cytogenetics laboratories. Those which had second-trimester maternal serum screening analyte measurements were further evaluated. Maternal serum analyte levels for each case and five matched controls were statistically analysed by matched ranked-sum analysis. 28 cases of fetal trisomy 13 were identified. The median AFP, uE3 and hCG levels were 1.35 MoM, 0.71 MoM and 0.90 MoM, respectively. Only uE3 levels were statistically different (p < 0.01) from those for the unaffected population. These data suggest that second-trimester maternal serum AFP, uE3 and hCG levels are not useful in detecting fetal trisomy 13 and protocols already existing for Down syndrome or trisomy 18 screening will not detect the majority of cases of this aneuploidy.     

Maternal serum unconjugated oestriol and human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down's syndrome.

OBJECTIVE--To investigate maternal serum unconjugated oestriol (uE3) and human chorionic gonadotrophin (hCG) levels in twin pregnancies and to consider the implications of the results for antenatal screening for Down's syndrome. DESIGN--Measurement of maternal serum uE3 and hCG levels from 15-22 weeks of gestation in twin and singleton pregnancies. Previously available maternal serum alpha-fetoprotein (AFP) levels were also presented. SETTING--Stored serum samples collected from women receiving routine antenatal care in Oxford were used. SUBJECTS--200 women with a twin pregnancy and, for each, three singleton control pregnancies matched for gestational age (same completed week of pregnancy) and duration of storage of the serum sample (same calendar quarter). RESULTS--The median uE3, hCG and AFP levels in the twin pregnancies were respectively, 1.67 (95% CI 1.56-1.79), 1.84 (95% CI 1.64-2.07) and 2.13 (95% CI 1.97-2.31) multiples of the median (MoM) for singleton pregnancies at the same gestational age. The variance of values for the three serum markers (expressed in logarithms), and the correlation coefficients between any two, were similar in the twin and singleton pregnancies. CONCLUSION--In maternal serum screening programmes for Down's syndrome dividing uE3, hCG and AFP MoM values in twin pregnancies by the corresponding medians for twin pregnancies will, in expectation, yield a similar false-positive rate in twin pregnancies as in singleton pregnancies.     

Amniotic fluid fibrinolytic system in fetal neural tube defects

Second trimester amniotic fluid fibrinolytic system was examined in normal pregnancies and those complicated by anencephaly, spina bifida and fetal chromosome abnormalities. No significant difference was demonstrated between the fibrinolytic systems from normal pregnancies and those complicated by fetal chromosome abnormalities. In pregnancies complicated with anencephaly and spina bifida no significant difference was demonstrated for alpha-1-antitrypsin, alpha-1-antichymotrypsin and urokinase. Plasminogen was significantly lower (p less than 0.02) and plasmin significantly higher (p less than 0.001) than levels from normal amniotic fluid. Alpha-2-macroglobulin, fibrinogen, FDP-D and FDP-E were detected only in pregnancies complicated with anencephaly and spina bifida.     

Second trimester maternal serum hCG level in an Asian population: normal reference values by ultrasound dating

OBJECTIVE: To establish normative data of maternal serum chorionic gonadotropin (hCG) during the second trimester in an Asian population. METHODS: We measured the maternal serum hCG levels in 17,955 normal singleton pregnancies between 15 and 21 weeks of gestation. The gestation age was estimated by measurement of fetal biparietal distance (BPD) in all cases. Median values of hCG at various gestational weeks were calculated and the values of hCG were converted to multiple of median (MoM). The incidences of low MoM value and high MoM value were also calculated. RESULTS: The mean and median values of hCG were 57,153 mIU/ml and 50,120 mIU/ml, respectively, at 15 weeks of gestation and then decreased to 30,898 mIU/ml and 26,226 mIU/ml, respectively, at 21 weeks. We found 8.6% and 9.4% of normal singleton pregnancies have hCG MoM values >2.0 MoM and <0.5 MoM, respectively. CONCLUSIONS: Our report provides a normal reference data of second trimester maternal hCG levels by ultrasound dating in an Asian population.     

Data from an alpha-fetoprotein pilot screening program in Maine

In Maine, maternal serum alpha-fetoprotein (AFP) values equaled 2 or more multiples of the median in 4.8% of screened women. Between 2.0 and 2.9 multiples of the median repeat maternal serum AFP testing and sonography were comparable as the next diagnostic step; at 3 multiples of the median or higher sonography was superior. Sonography moved dates back in only ten singleton viable pregnancies with maternal serum AFP elevations; three of these had open fetal defects. Among singletons, all five anencephaly cases, one of two open spina bifida lesions, and all three open ventral wall defects were identified. Three closed singleton neural tube defects and two open spina bifida defects in twins were not detected. Nineteen of 36 multiple gestations had maternal serum AFP 2 or higher multiples of the median. In singletons, maternal serum AFP of 3 or higher multiples of the median indicated a thirtyfold increased risk for fetal death and a sevenfold increased risk for birth weight under 2500 g.     

Cut-off levels for maternal plasma alpha-fetoprotein in the diagnosis of neural tube defects: validation of the use of multiples of the normal median.

A retrospective study was made of measurement of maternal plasma alpha-feto-protein (AFP) by a standard radioimmunoassay technique, as a method of screening for neural tube defects (NTDs) between 15 and 20 weeks gestation. There was a good fit of a log-normal distribution to the data at each week and multiples of the normal median were equivalent to constant centiles over weeks 15 to 20 and possibly at later weeks also. There were 700 plasma samples from women with normal prenancies and 60 from women with pregnancies complicated by fetal NTDs (30 with anencephaly and 30 with spina bifida). At 15 to 20 weeks of pregnancy, 90 per cent of women with fetuses affected by anencephaly, 70 per cent of those with fetuses affected by open spina bifida and 3 per cent ofthose with normal pregnancies had plasma AFP levels at or above 2.4 times the normal median for each gestational week. It was estimated that 2.1, 2.4 and 3.1 times the normal median maternal plasma AFP levels were equivalent to the 95th, 97th and 99th centiles respectively. The interassay coefficients of variation estimated on control sera throughout the entire study were 4 to 6 per cent.     

Ratio of immunochemically determined amniotic fluid acetylcholinesterase to butyrylcholinesterase in the differential diagnosis of fetal abnormalities

Summary. A total of 111 amniotic fluid samples, clear or blood stained, with elevated levels of alpha-fetoprotein and acetylcholinesterase was analysed by immunoassays specific for acetylcholinesterase and butyrylcholinesterase and the acetylcholinesterase/butyrylcholinesterase-ratios determined. Samples from 40 pregnancies associated with anen-cephaly, 47 pregnancies associated with open spina bifida or encephalocele and six pregnancies with fetal intrauterine death or miscarriage all had ratios of >0.14. All 11 pregnancies with fetal ventral wall defects had ratios <0.14 as had four pregnancies with normal outcome and elevated levels of alpha-fetoprotein and acetylcholinesterase. Three fetuses with both open spina bifida and ventral wall defects were associated with ratios above 0.14. These results suggest that immu-nochemical determination of acetylcholinesterase and butyrylcholinesterase can be used to distinguish pregnancies complicated by anencephaly, open spina bifida, encephalocele and miscarriage from those with ventral wall defects and samples with false positive elevated levels of alpha-fetoprotein and acetylcholinesterase. The procedure is accurate and simple to carry out and well suited to routine use in a clinical chemistry laboratory.     

A retrospective evaluation of second-trimester serum screening for fetal trisomy 18: experience of two laboratories.

A retrospective study on screening methods for fetal trisomy 18 has been carried out in two different laboratories using the serum parameters: total human chorionic gonadotropin (hCG), unconjugated oestriol (uE3), and alpha-fetoprotein (AFP) in different combinations and in single marker protocols. Laboratory A (L(A)) utilized a radio-immunoassay to examine 38 fetal trisomy 18 cases and laboratory B (L(B)) utilized an enzyme-immunoassay to examine 33 trisomy 18 cases. As unaffected references the whole routine cohorts of each laboratory were used (L(A): 29 043; L(B): 4264). In both trisomy 18 study groups the median hCG and uE3 multiples of the median (MoM) values were markedly declined (L(A): 0.21 MoM, 0.37 MoM; L(B): 0.31 MoM, 0.44 MoM). Even after exclusion of trisomy 18 cases with combined neural tube or ventral wall defects the medians of AFP MoM values were only moderately declined (L(A): 0.73 MoM; L(B): 0.8 MoM). Receiver-operator characteristic (ROC) curves after multivariate discriminance analysis and single marker evaluation demonstrated that the difference of efficiency between a combination of hCG, uE3 and AFP, and a combination of hCG and uE3 is small but that any of these combinations are more efficient than a combination of hCG and AFP or single marker protocols, respectively. At a risk cut-off generating a false-positive rate of one per cent the most effective marker combination detected 31 of 38 (81.6 per cent) affected pregnancies in L(A) and 25 of 33 (75.8 per cent) in L(B). The differences in sensitivity and specificity seem to be due to the different analytical systems being utilized by the two laboratories.     

Midtrimester triple test levels in women with severe preeclampsia and HELLP syndrome

BACKGROUND: The levels of midtrimester triple test constituents are known to be altered in hypertensive disorders of pregnancy. OBJECTIVE: Our aim was to determine whether midtrimester triple test constituent levels differ in women with severe preeclampsia and those who also develop HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome. METHODS: A retrospective chart analysis of 106 women with severe preeclampsia for whom midtrimester triple test data were available was made. None of these patients had fetuses with abnormal karyotype, nor did they deliver infants with malformations. The levels of midtrimester maternal serum alpha-fetoprotein (MSAFP), human chorionic gonadotropin (MShCG) and unconjugated estriol (MSuE3) of 74 patients with severe preeclampsia were compared with those of 32 patients who also developed HELLP syndrome. RESULTS: The mean MShCG was significantly higher and the mean MSuE3 was significantly lower in patients with HELLP syndrome than in those with only severe preeclampsia [1.78 multiple of the medians (MoM), standard error (SE) 0.18 vs. 1.27 MoM, SE 0.07, p=0.015 and 0.86 MoM, SE 0.05 vs. 1.04 MoM, SE 0.07; p = 0.03, respectively]. The two groups did not differ significantly with regard to MSAFP levels. CONCLUSION: Unexplained high levels of midtrimester MShCG and low levels of MSuE3 may be associated with the development of HELLP syndrome in women with severe preeclampsia.     

Second-trimester double or triple screening for Down syndrome: a comparison of Chinese and Caucasian populations.

OBJECTIVES: To compare the performance of double screening (measuring maternal serum levels of alpha-fetoprotein [AFP] and total beta-human chorionic gonadotrophin [hCG] as markers for Down syndrome) with that of triple screening (also measuring levels of unconjugated estriol [uE3]) in the second trimester of pregnancy, and to compare ethnic variance between Chinese and Caucasian populations. METHODS: The study investigated 15096 normal singleton pregnancies and 24 pregnancies affected with Down syndrome. Frequency distributions of AFP, hCG, and uE3 levels were analyzed. Likelihood ratios (LRs) were calculated using the multiple of median value (MoM) of AFP, hCG, and uE3 as variables. After multiplying maternal age risk by the LR values for the markers used in double and triple screening, the specific risks obtained with double and triple screening were estimated. The detection rate (DR) and false-positive rate (FPR) were calculated at different cut-off points. The serum markers' levels were also compared with those of Caucasian women. RESULTS: The median MoM value of hCG was higher in women with affected pregnancies (1.40) than those with unaffected pregnancies (1.00). However, the median MoMs of AFP and uE3 (0.79 and 0.68) were lower in affected than in unaffected pregnancies. At a FPR of 5%, the detection rates reached with double and triple screening were 50% and 66.7%, respectively. Ratios of the 3 serum markers' medians to those in a study with Caucasian women were 1.06 (range=1.04-1.09) for AFP, 1.14 (range=1.10-1.17) for hCG, and 1.28 (range=1.23-1.41) for uE3 for the relevant gestational weeks. CONCLUSION: Triple screening performed better than double screening in the second trimester. Ethnic variance should be taken into account in Down syndrome screening.     

The composition of amniotic fluid in pregnancies complicated by fetal anencephaly or spina bifida.

The concentration of amniotic fluid glucose, total protein, sodium, potassium, calcium, magnesium and phosphate as well as amniotic fluid osmolality were measured in normal second trimester pregnancies and in second trimester pregnancies complecated by fetal anencephaly or spina bifida. Amniotic fluid glucose concentration was low in anencephaly, while phosphate and total protein were high; calcium concentration and osmolality were slightly elevated with spina bifida. The application of these findings to antenatal diagnosis are discussed.     

Amniotic fluid gel cholinesterase density ratios in fetal open defects of the neural tube and ventral wall

Summary. Densitometry was used to measure gel acetyl- and pseudo-cholinesterase bands in a selection of amniotic fluid samples yielding positive α-fetoprotein and positive gel acetylcholinesterase results. The samples were associated with the following conditions: 28 anencephaly (10 stained with fetal blood), 20 open spina bifida (3 stained with fetal blood), 10 open ventral-wall defects (2 stained with fetal blood) and 5 unaffected pregnancies (all stained with fetal blood). In samples not visibly stained with fetal blood, the ratio of the acetylcholinesterase density to the pseudo-cholinesterase density distinguished between open ventral-wall defects and open neural-tube defects: the former group all had values less than 0.13, while the latter all had values greater than that. In amniotic fluid samples which were stained with fetal blood the acetylcholinesterase/pseudo-cholinesterase ratio did not offer useful diagnostic information; results from unaffected pregnancies overlapped with those from pregnancies with both ventral-wall defects and open neural-tube defects.     

Effect of estimating gestational age by ultrasound cephalometry on the specificity of alpha-fetoprotein screening for open neural-tube defects

A total of 1268 women had a maternal serum alpha-fetoprotein (AFP) screening test for open neural-tube defects between 15 and 22 weeks gestation and a routine ultrasound examination at their first antenatal visit. All had a singleton infant without a neural-tube defect. AFP values were expressed as multiples of the normal median at the relevant gestational age (MoM). The percentage of women with raised maternal serum AFP levels was less when gestation was estimated by the fetal biparietal diameter (BPD) than when the time since the first day of the last menstrual period (LMP) was used; 1.8% compared with 2.3% at a serum AFP cut-off level of 2.5 MoM. Different ultrasound policies were compared for their effect on AFP screening and the best was found to be routine BPD measurement used together with a higher cut-off level than usual. For example, using a cut-off level of 3.0 MoM the detection rate for open spina bifida at 16-18 weeks gestation would be about 88% and the proportion of unaffected singleton pregnancies with raised levels only 0.9%. These results are materially better than those achieved by a policy of scanning only those women with a raised AFP level (79% and 1.4% respectively with a more conventional cut-off level of 2.5 MoM) or, in addition, scanning those with doubtful gestational ages (82% and 1.7% respectively with a cut-off level of 2.5 MoM).