Maternal Serum α-Fetoprotein Screening for the Detection of Neural Tube Defects—Report of a Pilot Program

We tested 10,715 low-risk pregnancies in a voluntary maternal serum α-fetoprotein screening program for the detection of neural tube defects in California. In all, 5.3 percent of women had one elevated serum level, 3.3 percent were referred for sonography and 1.5 percent for amniocentesis. There were 12 cases of open neural tube defects (1.1 per 1,000); all of the mothers had one elevated serum αfetoprotein level: nine (75 percent) completed the protocol and the neural tube defects were correctly identified. No normal pregnancies were terminated. The risk of an open neural tube defect occurring was about 1 in 50 after the first abnormal serum level and 1 in 15 at amniocentesis. We found significantly increased risk for fetal death and low birth weight after one elevated serum α-fetoprotein level, though the likelihood of a normal pregnancy outcome was about 80 percent. Maternal serum screening was also useful in identifying twin pregnancies and correcting underestimated gestational dates.     

Prevalence of neural tube defects in South Australia, 1966-91: effectiveness and impact of prenatal diagnosis.

OBJECTIVE--To determine trends in total prevalence of neural tube defects in South Australia during 1966-91, the impact of prenatal diagnosis on birth prevalence, and the effectiveness of prenatal screening for neural tube defects in 1986-91. DESIGN--All births and terminations of pregnancy affected by neural tube defects and information on prenatal screening were ascertained from multiple sources including the South Australian perinatal and abortion statistics collections, birth defects register, and state maternal serum alpha fetoprotein screening programme. SETTING--Southern Australia. SUBJECTS--All 1058 births and terminations of pregnancy affected by neural tube defects in 1966-91. MAIN OUTCOME MEASURES--Total prevalence and birth prevalence of individual and all neural tube defects. The proportion of screened cases detected prenatally. RESULTS--Total prevalence of neural tube defects during 1966-91 was 2.01/1000 births with no upward or downward trend. However, birth prevalence fell significantly (by 5.1% a year), with an 84% reduction from 2.29/1000 births in 1966 to 0.35/1000 in 1991 (relative risk = 0.16, 95% confidence interval 0.07 to 0.34). The fall was 96% for anencephaly and 82% for spina bifida. 85% of defects, both open and closed, were detected before 28 weeks'' gestation in women screened by serum alpha fetoprotein or mid-trimester ultrasonography, or both, in 1986-91 (99.0% for anencephaly and 75.7% for spina bifida). CONCLUSIONS--While the total prevalence of neural tube defects in South Australia remained stable, prenatal diagnosis and termination of pregnancy resulted in an 84% fall in birth prevalence during 1966-91. Screening detected over four fifths of cases in 1986-91.     

Maternal alpha-fetoprotein screening: two years' experience in a low-risk district.

Over a two-year period, 3479 pregnant women in the Kings'' Lynn Health District were screened for neural tube defects by estimation of maternal serum alpha-fetoprotein. Most pregnancies were scanned by sonar for fetal maturity. Eight women had fetuses with open neural tube defects; four with anencephaly were associated with very high alpha-fetoprotein values. Of the four with open neural tube defects without anencephaly, only one was detected by screening and confirmed after amniocentesis. One other had a raised serum alpha-fetoprotein but a normal amniotic fluid value. The other two affected fetuses were missed. This disappointing outcome was attributed to the poor predictive value of alpha-fetoprotein in detecting open neural tube defects (anencephaly apart) rather than to errors in its estimation or in assessment of fetal maturity by sonar scan. We question the validity of screening, particularly in areas of intermediate or low incidence.     

Birth prevalence and recurrence rates of neural tube defects in southern Alberta in 1970-81.

Given the observed variation in birth prevalence and recurrence rates of neural tube defects, it is important to obtain such data specific to a given locality for research and genetic counseling purposes. A review of hospital medical charts, the patient lists of the Medical Genetics and Myelomeningocele clinics at Alberta Children''s Hospital and data from the Canadian Congenital Anomalies Surveillance System revealed the annual birth prevalence rate of neural tube defects in southern Alberta in 1970-81 to be 1.62/1000 total births. This figure suggests southern Alberta to be a low-frequency area. There was no significant variation in the annual rates of spina bifida, encephalocele or all neural tube defects combined over the study period. A significant linear decline in the frequency of births of anencephalic infants, however, was noted (p = 0.025). Information on the total reproductive history of the mothers revealed that the empiric risk of recurrence of a neural tube defect was 2.2%, and the risk to all siblings was estimated to be 2.3%. In future prevalence studies multiple sources of case ascertainment should be used, including data on pregnancies terminated because of a fetal neural tube defect.     

Antenatal diagnosis of neural tube defects in Canada: extension of a collaborative study.

Experience with the diagnosis of neural tube defects from alpha1-fetoprotein (AFP) concentrations in amniotic fluid is reported from a prospective study of five laboratories testing for 13 Canadian genetic centres. The results of the study indicate that antenatal diagnosis of open neural tube defects is being carried out effectively in Canada (in 99.2% of cases the AFP measurements were interpreted correctly). Amniocentesis should be recommended to women at high risk for having a child with a neural tube defect (i.e., those who have a child, a parent or a sibling with a neural tube defect). The rate of neural tube defects in 182 high-risk pregnancies was 2.2% for an open defect and 1.1% for a closed defect, whereas the rate in 673 pregnancies in which amniocentesis was being performed for other reasons was 0.3%. This suggests that the AFP concentration should be measured in any sample of amniotic fluid collected for other reasons (usually fetal karyotyping). There were three instances of false-negative results, for a rate of 0.4%. Two closed neural tube defects were not detected; this limitation of the test has also been found by others. One of the six fetuses with an open neural tube defect, who died in utero, had a large myelocele in the neck that was not recognized. There were also four instances of false-positive results, for a rate of 0.5%. The findings suggest that AFP values that are more than 2 but less than 7 standard deviations (SDs) above the mean may indicate a neural tube defect, and that values 7 or more SDs above the mean very likely indicate such a defect, although other reasons for such high values (e.g., fetal erythrocytes in the amniotic fluid, intrauterine death and mistaken gestational age) must be ruled out by other methods.     

Maternal fever and neural tube defects

It has been proposed that hyperthermia in the pregnant woman is associated with neural tube defects in her offspring. We analyzed retrospective interview data for a maternal history of probable febrile illness during the first trimester of pregnancy among mothers of infants with anencephaly or spina bifida. There were two control groups--mothers of infants with Down syndrome and mothers of infants with cleft lip or palate. With the Down syndrome group serving as controls, the incidence of febrile illness among mothers of all infants with neural tube defects was significantly elevated. With the cleft group as controls, the fever incidence was not significantly increased in the neural tube defect groups. When the combined cleft and Down syndrome controls were used, only mothers of the spina bifida group had an elevated fever incidence. Epidemiology data suggest an association of maternal fever during pregnancy with neural tube defects in the offspring.     

Behavioral effects of prenatal folate deficiency in mice

BACKGROUND: Folate supplementation decreases the incidence of birth defects such as neural tube defects (NTDs). We and others have shown that gestational dietary folate deficiency that does not produce overt NTDs can alter fetal neural histology. Accordingly, murine offspring were examined for the possible functional consequences of prenatal folate deficiency. METHODS: CD-1 mice were fed a diet of chow containing 400, 600, or 1200 nmol of folic acid/kg of chow for eight weeks prior to breeding and until GD18, at which time all dams were placed on folate-replete chow. Behavioral tests of male and female offspring included righting reflex, negative geotaxis, forelimb hanging, motor coordination, open field activity, and elevated plus maze activity. RESULTS: Of greatest significance, the adult offspring that were prenatally folate-deficient exhibited more anxiety-related behavior in the elevated plus maze. Offspring of the 400 nmol of folic acid/kg of chow diet group exhibited significantly shorter durations in the open arms and longer durations in the closed arms. Further, these two behaviors were dose-related. There was also a trend for the prenatally folate-deficient adult mice to exhibit more thigmotaxis (wall-hugging) behavior in the open field, entering the central area less frequently than controls. There were few other differences in tested behaviors between folate-deficient and folate-replete mice. CONCLUSIONS: Prenatal folate deficiency that is repleted at birth can manifest later with increased anxiety 9-12 weeks after birth.     

Ascertainment of pregnancies terminated because of birth defects: effect on completeness of adding a new source of data

BACKGROUND: When evaluating preventive programs such as folate promotion and rubella vaccination, it is critically important to include terminations of pregnancy for neural tube defects and congenital rubella syndrome. Data from birth defects registries are often used for this purpose. The Western Australian Birth Defects Registry ascertains cases of birth defects in livebirths, stillbirths, and terminations of pregnancy for fetal abnormality, using multiple sources of ascertainment. METHODS: Data on terminations of pregnancy for fetal abnormality from the Western Australian Hospital Morbidity Data System 1980-1997 (not previously available to the Registry) were used to estimate the completeness of ascertainment of such cases by the Registry. Ascertainment-adjusted prevalences were calculated using capture-recapture methods. RESULTS: A total of 702 terminations with birth defects were identified among hospital discharges, most of which were already known to the Registry (87.9%). Of the 85 new cases, seven had a neural tube defect, 23 had a chromosomal defect, and 12 had confirmed maternal rubella infection during pregnancy. The ascertainment-adjusted prevalence was not importantly [corrected] different for birth defects overall or for these individual conditions, although the 95% confidence intervals for all birth defects, and for all chromosomal defects, did not include the prevalence based on registered cases only. CONCLUSIONS: The Western Australian Birth Defects Registry ascertains a high proportion of pregnancies terminated for fetal abnormality, and should therefore be a reliable source of data with which to assist in monitoring the effectiveness of preventive programs.     

Maternal serum alpha-fetoprotein screening programs and quality control for laboratories performing maternal serum and amniotic fluid alpha-fetoprotein assays: policy statement. American Society of Human Genetics.

Maternal serum alpha-fetoprotein (MSAFP) values are used primarily but not solely to predict the occurrence of open neural tube defects in the fetus; their use for prediction of Down''s syndrome is a new initiative under investigation. The test is a good one, as far as such a test can be, but it is imperfect, because false-negative and false-positive results both occur. In other words, it is not an infallible test. To use the test as effectively as is currently possible requires a program capable of supplying baseline values in sufficient number and the follow-up procedures necessary for interpretation of positive tests. In other words, it is not simply an office test. Because there is no effective treatment to relax the burden of neural tube defects in the large majority of patients, prevention of disease involves termination of pregnancy at present. In other words, use of the test is value laden and controversial for some sectors of society. Despite its imperfections, the need for an elaborate societal structure to apply it, and its value-laden context the test is considered by many as a necessary procedure to maintain normal standards of practice. Indeed, the American College of Obstetricians and Gynecologists issued a statement advising its fellows to be aware of the availability of MSAFP testing and to discuss such testing with patients. It is natural that confusion about protocol and anxiety about practice and its consequences are prevalent in this context. The American Society of Human Genetics (ASHG) offers here a statement about issues that affect MSAFP testing and the attendant pitfalls.     

International retrospective cohort study of neural tube defects in relation to folic acid recommendations: are the recommendations working?

Objectives To evaluate the effectiveness of policies and recommendations on folic acid aimed at reducing the occurrence of neural tube defects.Design Retrospective cohort study of births monitored by birth defect registries.Setting 13 birth defects registries monitoring rates of neural tube defects from 1988 to 1998 in Norway, Finland, Northern Netherlands, England and Wales, Ireland, France (Paris, Strasbourg, and Central East), Hungary, Italy (Emilia Romagna and Campania), Portugal, and Israel. Cases of neural tube defects were ascertained among liveborn infants, stillbirths, and pregnancy terminations (where legal). Policies and recommendations were ascertained by interview and literature review.Main outcome measures Incidences and trends in rates of neural tube defects before and after 1992 (the year of the first recommendations) and before and after the year of local recommendations (when applicable).Results The issuing of recommendations on folic acid was followed by no detectable improvement in the trends of incidence of neural tube defects.Conclusions Recommendations alone did not seem to influence trends in neural tube defects up to six years after the confirmation of the effectiveness of folic acid in clinical trials. New cases of neural tube defects preventable by folic acid continue to accumulate. A reasonable strategy would be to quickly integrate food fortification with fuller implementation of recommendations on supplements.     

Associated malformations in cases with neural tube defects

Infants with neural tube defects (NTDs) may have other associated congenital defects. The reported incidence and the types of associated malformations vary between different studies. The purpose of this investigation was to assess the prevalence of associated malformations in a geographically defined population. The prevalences at birth of associated malformations in infants with NTDs were collected between 1979 and 2003 on all infants born in the area covered by the registry of congenital anomalies of Northeastern France in 334,262 consecutive births. Of the 360 infants with NTDs born during this period, 20.5 % had associated malformations. Associated malformations were more frequent in infants who had encephalocele (37.5 %) than in infants with anencephaly (11.8 %) or infants with spina bifida (23.7 %). Malformations in the face (oral clefts), in the musculoskeletal system, in the renal system, and in the cardiovascular system were the most common other anomalies. In conclusion the overall prevalence of malformations, which was one in five infants, emphasizes the need for a thorough investigation of infants with NTDs. A routine screening for other malformations especially facial clefts, musculoskeletal, renal and cardiac anomalies may need to be considered in infants with NTDs, and genetic counseling seems warranted in most of these complicated cases.     

Can we afford screening for neural tube defects? The South Wales experience.

Clinical and financial gains and losses accruing from five different options for screening for open neural tube defects were estimated, based principally on the results of detailed monitoring of inputs and outcomes and of process costs in the South Wales Anencephaly and Spina Bifida Study. As well as estimating the overall clinical costs of a screening service it was shown that if the prevalence, including terminations, of open neural tube defects is between 1.25 and five per 1000 births the financial cost of avoiding the birth of a seriously handicapped child who would survive for more than 24 hours is in the range 9000 pounds- 54000 pounds depending on the option adopted and the prevalence of the condition in the target population. Prevalence is the biggest determinant of cost. The data should provide a basis for assessment and discussion of resource priorities in the National Health Service.     

Reduction in Valproic Acid–Induced Neural Tube Defects by Maternal Immune Stimulation: Role of Apoptosis

Teratogenic deregulation of apoptosis during development is a possible mechanism for birth defects. Administration of valproic acid (VA) during first trimester of pregnancy causes neural tube defects (NTDs). Nonspecific stimulation of the mother's immune system has been shown to reduce various teratogen‐induced fetal malformations including NTDs in rodents. This present study investigated the role of reduced apoptosis by maternal immune stimulation in prevention of VA‐induced NTDs in CD‐1 mice. Prevention of VA‐induced NTDs by nonspecific maternal immune stimulation using IFNγ was employed to evaluate the role of reduced apoptosis by IFNγ in this protective mechanism. Apoptosis was quantified using flow cytometry. Terminal Transferase dUTP Nick End Labeling assay was used to localize the apoptosis. Increased apoptosis, suggesting involvement in VA teratogenicity, was observed along the neural tube in both normal and abnormal embryos from VA‐exposed dams. Increased apoptosis in normal VA‐exposed embryos suggests that VA may alter other cellular processes such as cell proliferation and differentiation in addition to apoptosis. Apoptotic levels in embryos with closed neural tubes from IFNγ + VA dams were similar to controls indicating resistance to VA‐induced apoptosis and protection against teratogenicity of VA. In IFNγ + VA exposed embryos with open neural tubes, maternal immune stimulation failed to regulate apoptosis resulting in an NTD. Overall, these results suggest that VA alters several biological processes including apoptosis in the developing embryos to induce fetal malformations. Resistance to VA‐induced apoptosis in embryos resulting from maternal immune stimulation may be involved in protective mechanism.     

Maternal serum alpha-fetoprotein screening for neural tube defects and other disorders using an ultramicro-ELISA

Summary In Cuba and in the German Democratic Republic (GDR) a total of 24,412 pregnant women were tested for maternal serum alpha-fetoprotein (MSAFP) at the 16th to 20th week of gestation. An inexpensive and partly automated ultramicroliter enzyme immunoassay (ELISA) with final volumes of 10l was used to analyze simultaneously 50 samples. The intraassay coefficient of variation (CV) of 5–8% and day/day CVs of 6–10.5% were obtained with a test frequency of 320 assays/day. A cut-off level of twice the median value (MoM) was chosen. An amniocentesis was done in a total of 0.5% (in the GDR) and 0.7% (in Cuba) of the screened women. The prevalence of open neural tube defects (ONTD) was calculated from the present study and was 1.43 in Cuba and 1.34 in the GDR. Through MSAFP screening 88.2% ONTD were detected. There was no therapeutic abortion of a normal fetus. The approximate cost for this program was about 2.36 marks-GDR per patient screened, or about 2,048 marks per ONTD detected.     

Evaluation of birth defect histories obtained through maternal interviews.

Etiologic studies of birth defects often use family history information provided by parents of patients. The validity of this information has not been adequately assessed. Using data from the Atlanta Birth Defects Case-Control study, we evaluated sensitivity, specificity, and positive predictive value of mothers' responses regarding the presence of birth defects in their offspring. A total of 4929 mothers of infants with major structural defects ascertained by the Metropolitan Atlanta Congenital Defects Program and a total of 3,029 mothers of normal infants were asked whether their babies had had a birth defect or a health problem diagnosed during the first year of life. Interviewers and coders of maternal responses were blinded to the case-control status of infants. Sensitivity (the proportion of case mothers who gave responses that could be coded as denoting a major birth defect) was 61%. Specificity (the proportion of control mothers who gave responses that could not be coded as denoting a major birth defect) was 98%. The positive predictive value (the proportion of mothers who gave a major-birth-defect response who in fact had babies with major birth defects) was estimated as 47%. Sensitivity, specificity, and positive predictive value varied by maternal sociodemographic factors such as race and education, as well as by type of defect. These results suggest that family history data obtained through maternal interviews should be cautiously interpreted and, if not properly validated, may alter estimates of recurrence risks.     

The risk of birth defects in dichorionic twins conceived by assisted reproductive technology.

The purpose of this study was to examine whether dichorionic twins conceived by assisted reproductive technology (ART; intracytoplasmic sperm injection [ICSI], in vitro fertilization [IVF], gamete-intrafallopian tube transfer [GIFT]) have a higher risk of birth defects compared to dichorionic twins conceived naturally. We reviewed the medical records of 406 mothers with dichorionic twin pregnancies, who received continuous antenatal care from < or = 20 weeks of gestation and gave birth to infants after > or = 24 weeks of gestation in our institute. Birth defects were diagnosed at the time of hospital discharge according to the International Classification of Diseases, 10th Revision. Occurrence of birth defects was compared between twins conceived by ART and those conceived naturally using logistic regression analysis. Overall, 51 of 812 infants (51/812 = 6.2%) had birth defects. The incidence of birth defects in ART-conceived twins was significantly higher than that of naturally conceived twins with an odds ratio of 6.9 (95% confidence interval [CI] 2.1, 22.5), 3.7 (95% CI 1.2, 12.0), and 4.3 (95% CI 1.4, 14.3) for ICSI, IVF, and GIFT, respectively. The higher frequency of birth defects in ART-conceived twins was still significant after adjusting for higher maternal age in the ART group, with an adjusted odds ratio of 6.7 (95% CI 2.1, 21.9), 3.6 (95% CI 1.1, 11.5), and 3.7 (95% CI 1.2-11.8) for ICSI, IVF, and GIFT, respectively. Dichorionic twins conceived by ART, compared to dichorionic twins conceived naturally, had a much higher risk for birth defects diagnosed at hospital discharge.     

Light microscopic and ultrastructural observations in advanced stages of induced exencephaly and spinal bifida.

This investigation was performed to demonstrate the morphologic basis of the elevation of fetal proteins in the amniotic fluid of fetuses with neural tube defects. Pregnant rats were treated with hypervitaminosis. A to induce exencephaly or with trypan blue to produce spina bifida aperta. The malformations were studied on days 15-20. On day 15 of gestation, edema developed in the primitive nervous tissue. This was followed by the appearance of quickly expanding hemorrhages throughout the ventricular and intermediate zones. Some capillaries did not rupture but collapsed and showed degenerative changes of the endothelium, probably due to lack of blood perfusion. The ventricular layer in exencephaly and spina bifida aperta was exposed to the amniotic cavity due to non closure of the neural tube. On day 17, this superficial lining of the primitive nervous tissue was disrupted by the expanding hemorrhages and subsequent necrosis. As a result vast amounts of fetal blood and cell debris were extruded into the amniotic fluid. During days 18 to 20, the degeneration of the nervous tissue proceeded rapidly. This process showed the same features in the ventricular cells, the primitive neurons and the neurons. Initially it was characterized by condensation of the nuclear chromatin and the cytoplasm, irregular outlines and breakdown of the plasma membrane. Only part of the cell debris was phagocytozed by macrophages. It is concluded that the leakage of fetal serum and cell debris causes the elevation of fetal protein levels in the amniotic fluid of fetuses with open neural tube defects.     

Significance of the maternal levels of serum alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol in various congenital developmental defects in pregnancy trimester II]

Maternal serum alpha-fetoprotein (MSAFP), human chorionic gonadotropin (hCG) and unconjugated oestriol (uE3) concentrations were measured in maternal serum samples from 21 pregnancies with neural-tube defects, 4 pregnancies with ventral wall defects (VWD) and 1662 unaffected pregnancies in women. These congenital malformations were confirmed by ultrasound scanning. The mean multiplate of the median (MoM) for AFP and uE3 was significantly different from the control values in cases of open NTD (AFP median MoM = 5.95, p < 0.001, uE3 median MoM = 0.2, p < 0.001), while hCG values did not differ from those of matched controls (hCG median MoM = 0.9). The biological basis of altered levels of uE3 in pregnancies with fetal NTDs is unclear.     

Alpha-fetoprotein and albumin in experimentally-induced exencephaly in the rat.

Alpha-fetoprotein and albumin were quantified in the sera and amniotic fluids from control, Vitamin A-treated non-exencephalic and Vitamin A-treated exencephalic rat fetuses. Exencephaly was associated with amniotic fluid alpha-fetoprotein concentrations which were significantly elevated over those of Vitamin A-treated non-exencephalic and of untreated fetuses. Amniotic fluid albumin concentrations also were higher in the exencephalic fetuses than in the non-exencephalic fetuses. Serum alpha-fetoprotein and albumin concentrations were lower in the exencephalic than in the non-exencephalic fetuses. The results are cosistent with simple diffusion across a defective barrier as the cause of elevated amniotic fluid alpha-fetoprotein concentrations in the presence of open neural tube defects. This experimental model of neural tube defects result in changes in amniotic fluid alpha-fetoprotein similar to those changes found in human amniotic fluid alpha-fetoprotein concentrations in the presence of neural tube defects.     

Birth Prevalence of Neural Tube Defects and Orofacial Clefts in India: A Systematic Review and Meta-Analysis

Background

In the last two decades, India has witnessed a substantial decrease in infant mortality attributed to infectious disease and malnutrition. However, the mortality attributed to birth defects remains constant. Studies on the prevalence of birth defects such as neural tube defects and orofacial clefts in India have reported inconsistent results. Therefore, we conducted a systematic review of observational studies to document the birth prevalence of neural tube defects and orofacial clefts.

Methods

A comprehensive literature search for observational studies was conducted in MEDLINE and EMBASE databases using key MeSH terms (neural tube defects OR cleft lip OR cleft palate AND Prevalence AND India). Two reviewers independently reviewed the retrieved studies, and studies satisfying the eligibility were included. The quality of included studies was assessed using selected criteria from STROBE statement.

Results

The overall pooled birth prevalence (random effect) of neural tube defects in India is 4.5 per 1000 total births (95% CI 4.2 to 4.9). The overall pooled birth prevalence (random effect) of orofacial clefts is 1.3 per 1000 total births (95% CI 1.1 to 1.5). Subgroup analyses were performed by region, time period, consanguinity, and gender of newborn.

Conclusion

The overall prevalence of neural tube defects from India is high compared to other regions of the world, while that of orofacial clefts is similar to other countries. The majority of studies included in the review were hospital based. The quality of these studies ranged from low to moderate. Further well-designed, high quality community-based observational studies are needed to accurately estimate the burden of neural tube defects and orofacial clefts in India.