Detection Of Neural Tube Defects Research Articles

Antenatal attendance and screening for neural tube defects.

An analysis of factors influencing the time of booking at seven hospital antenatal clinics in one Health Authority Area showed that only 52.5 per cent of patients booked before 16 weeks gestation and 78.9 per cent before 19 weeks gestation. The principle reasons for late booking were delay in the patient seeking medical advice and delay in referral to hospital by the general practitioner (GP) after pregnancy was confirmed. Possibilities for improving early attendance and hence implementing an effective screening programme for the detection of neural tube defects are discussed.

Pregnancies associated with low maternal serum alpha-fetoprotein concentrations

PIP: A program of routine screening for antenatal detection of neural tube defects by alpha fetoprotein (AFP) testing is described. It was decided to determine the outcome of all pregnancies in which the patients exhibited a low AFP level during the screening process. From May 1975 to September 1976, 3% (53 cases) of the 2100 women tested had low AFP levels. Since maternal serum AFP levels rise with increasing gestational age until 32 weeks, a large number of women with low AFP levels actually have gestational ages more advanced than originally thought. That was true in this test. Ultrasonic examination of the cases with low AFP levels halped in revision gestational ages for some of the women. Among the 49 women with low AFP levels at gestational ages from 12-16 weeks, 12% had a spontaneous abortion eventually, 2% (or 1 case) had a macerated stillborn infant, and 1 woman was not pregnant. All 4 of the women with low AFP levels at gestational ages above 16 weeks had their gestational ages revised downward following ultrasonic examination. The study show that most women with low AFP levels eventually deliver a normal infant; a low AFP level does appear to be associated with spontaneous abortion. A larger study might identify association with other abnormalities. The study data was graphed and tabulated.

Maternal serum alpha-fetoprotein screening: Promise not yet fulfilled

Measurement of alpha fetoprotein (AFP) levels in amniotic fluid has been used as a diagnostic tool for detection of neural tube defects (NTDs) in the fetus. AFP measurement in conjunction with ultrasonography yields a 90% NTD detection rate. The technique is recommended for use in pregnancies known to be at risk of NTDs and as a screening technique for use with 2nd-trimester amniocentesis. In recent years, maternal serum AFP assays have been used for NTD detection. The technique has promise as a diagnostic tool but is not recommended for routine maternal screening. Problems with maternal AFP screening are: 1) the large number of false positive results; 2) lack of general patient and physician education on the screening technique; 3) technical problems related to the assay; 4) inconsistency of assay results from 1 laboratory to another; and 5) the lack of established normal standards for the test.

Factors affecting the success of mid-trimester amniocentesis

Of 298 women who had mid-trimester amniocentesis carried out in a single hospital unit in a 6-yr period, an increasing proportion were carried out for detection of neural tube defects. A clinical decision could be made following the first amniocentesis in 77% of cases. There were 16% where liquor was not obtained at the first attempt, and a further 7% where cell growth or biochemical testing was unsatisfactory. The outcome was influenced by the experience of the operator and timing of procedure. The success of the first procedure was 59% before 16 wk of gestation and 86% between 16 and 20 wk. The incidence of blood-staining of the liquor was higher with an anterior placenta (19%). Despite difficulties, the abortion rate (3.5%) does not appear to be higher than would be expected.

Prenatal detection of neural tube defects: False positive and negative results

An estimated 6,000 to 8,000 babies with neural tube defects (NTDs) are born each year in the United States. The suffering of both child and family has been well documented.1-3 Prenatal detection early in the second trimester of pregnancy became possible in 1972 when elevated α-fetoprotein (AFP) concentrations in amniotic fluid in association with open NTDs were demonstrated in Edinburgh.4 These results have been amply confirmed.5-10 The AFP test is best used and most reliable between 14 to 16 weeks of gestation.8 With such prenatal diagnosis, termination of the abnormal pregnancy can be offered to the family. AFP is synthesized by the yolk sac and fetal liver and normally passes from the fetal serum into fetal urine and then into the amniotic fluid.

Prenatal Diagnosis of Neural Tube Defects

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.

Prenatal detection of neural tube defects: Comparison between alpha-fetoprotein and beta-trace protein assays

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 β-trace protein asseys on amniotic fluid samples from defective fetuses was compared to alpha-fetoprotein studies. At present, alpha-fetoprotein studies provide more reliable results.

The present status of prenatal detection of neural tube defects

In experimentally induced myelocele in rats, efforts to find neural cells in amniotic fluid (AF) were unsuccessful. Creatine phosphokinase (CPK) and aldolase concentrations studied in serum of 118 and cerebrospinal fluid (CSF) in 9 patients with myelomeningocele showed serum CPK to be significantly elevated and more responsive to additional muscle injury than aldolase, but both enzymes appeared in lower concentrations in patients with myelomeningocele than those with infantile atrophy or cerebral palsy. In CSF, CPK, and aldolase concentrations averaged 4.2 I.U. and 2.7 S.L.U. per milliliter, respectively. Significant CPK elevation (p < 0.001) was also found in AF from myeloschitic fetuses and maternal rat serum. Although these findings suggest that increased CPK concentration is an indicator of myelocele in rats, the technique is impractical for prenatal detection of human neural tube defects (NTD) because muscle denervation in the human fetus occurs too late in gestation. This does not, however, preclude the value of CPK for detecting onset of paraparesis. In all myeloschitic human fetuses, the CSF communicates directly with AF for at least 3 to 4 weeks. This implies that CSF is probably the principal source of increased alphafetoprotein concentration encountered in AF of all pregnancies with NTD. When biological variables are recognized, it is evident that increased concentration of amniotic fluid alpha fetoprotein is a reliable indicator of fetuses with open myelocele and/or anencephalus.