|Year : 2016 | Volume
| Issue : 1 | Page : 6-10
The prevalence of neural tube defects in North-West Nigeria
Daniel Chukwunyere Nnadi, Swati Singh
Department of Obstetrics and Gynaecology, Usmanu Danfodiyo University Teaching Hospital, Sokoto, Nigeria
|Date of Web Publication||23-May-2016|
Daniel Chukwunyere Nnadi
Department of Obstetrics and Gynaecology, Usmanu Danfodiyo University Teaching Hospital, Sokoto
Source of Support: None, Conflict of Interest: None
Background: Neural tube defects (NTDs) consist of a variety of central nervous system abnormalities, most of which result from a lack of closure of the neural tube. Aims and Objectives: The study aimed to determine the prevalence of NTDs among women delivering in the labor room suites of a tertiary health institution in North-Western Nigeria. Subjects and Methods: This was a 3-year prospective study carried out in the Department of Obstetrics and Gynecology in association with the Department of Pediatrics. All neonates delivered in the labor rooms were examined for NTDs soon after birth. Those diagnosed with NTDs were admitted into the special care baby unit for observation and documentation. Results: There were 10, 163 deliveries and NTDs were present in 22 cases, thus giving a prevalence of 2.2/1000 deliveries. The common types of NTDs were spina bifida 72.7% (16/22), anencephaly 22.7% (5/22), and encephalocele 4.6%. There was a preponderance of females, with a female to male ratio of 1.4:1. Hydrocephalus was the most common associated anomaly 36.4% (8/22). The mothers were mainly within the age range of 20-35 years 59.1% (13/16), parity 2 or more and of low-socioeconomic status. Diagnoses were made by antenatal ultrasonography 50% (11/22) and clinically (50%) after delivery. The perinatal mortality was 81.8% (18/22). Conclusion: The prevalence of NTDs in this study is in consistent with literature. Improvement in maternal nutrition and antenatal folate intake is recommended.
Keywords: Neural tube defects, Nigeria, prevalence
|How to cite this article:|
Nnadi DC, Singh S. The prevalence of neural tube defects in North-West Nigeria. Saudi J Health Sci 2016;5:6-10
| Introduction|| |
The term neural tube defect (NTD) is applied to a variety of central nervous system (CNS) abnormalities, most of which result from a lack of closure of the neural tube. Worldwide, the prevalence of NTDs is approximately 1-5/1000 live-births and the risk of recurrence is 2-3%.  The reported incidence of NTDs varies from country to country and even with regions in the same country.  An incidence of 7.33/1000 births have been reported in India, 0.6-1.3 in the USA, whereas in Nigeria rates of 2.75 to 7/1000 births have been reported. ,,, The highest reported incidence is in Northern china. 
In humans, formation of the neural tube begins in the 3 rd week after fertilization and requires that the top layers of the embryonic germ disc elevate as folds and fuse in the midline. , The phenomenon is complex, involves numerous cell processes, and is often disrupted, resulting in NTDs. The process of neural tube formation is called neurulation, and it is responsible for establishing the brain and spinal cord regions down to the lowest sacral level. NTDs occur because of a defect in the neurulation process. , These defects may occur cranially, causing anencephaly, which is fatal, or caudally, usually in the lumbosacral area, causing spina bifida cystica (myelomeningocoele, meningocoele, and spina bifida occulta).
NTD can be classified based on embryological considerations and the presence or absence of exposed neural tissue, as open or closed. Open NTDs result from defective primary neurulation while defective secondary neurulation gives rise to closed NTDs. In open variety (meningoceles or meningomyelocele), the entire CNS is involved; neural tissue is exposed with associated cerebrospinal fluid leakage.  Closed NTDs are localized and confined to the spine (brain rarely affected).  Neural tissue is not exposed, and the defect is fully epithelized, although the skin covering the defect may be dysplastic. ,,, The most severe are "open" defects in which neural tissue is exposed. , Depending on the level of the lesion, interruption of the spinal cord at the site of the spina bifida defect causes paralysis of the legs, incontinence of urine and feces, anesthesia of the skin and abnormalities of the hips, knees and feet.
Most NTDs are multifactorial in origin, having both genetic and environmental components.  A strong genetic component is indicated by the recurrence risk for siblings of affected individuals.  Mis-regulation of any of a number of different genes may result in an NTD. Other genes like the homocysteine remethylation gene MTHFR for 5, 10-methylene tetrahydrofolate reductase that catalyzes the reduction of folate as part of the methylation pathway, appears to play a role in some NTDs in Dutch and Irish populations. 
Risk factors include family history, it may occur as a number of different syndromes or chromosomal anomalies.  Two additional abnormalities often associated with NTDs include hydrocephalus and the Arnold-Chiari type 11 malformation.  The majority of NTDs are nonsyndromic and are not associated with other congenital malformations. 
To the best of our knowledge, no study on NTDs has been carried out in our institution. This study aims to determine the prevalence and types of NTDs identify subgroups that are disproportionately affected and provide information that may help to prevent recurrence.
| Subjects and methods|| |
The study was performed at the Department of Obstetrics and Gynecology in association with the Department of Pediatrics of the Usmanu Danfodiyo University Teaching Hospital, Sokoto a tertiary health institution in North-West Nigeria.
This was a 3-year prospective study conducted in the two labor room suites of the Department of Obstetrics and Gynecology and the special care baby unit (SCBU) of the Pediatrics Department from January 1, 2011 to December 31, 2013. The hospital has 600-bed spaces and provides tertiary and secondary health care services to neighboring states and also runs a residency training program for doctors in the various sub-specialists including surgery, obstetrics and gynecology, internal medicine, pediatrics, among others. All neonates delivered in the labor rooms were examined for congenital abnormalities soon after birth with an emphasis on NTDs. The study group included all live-births along with stillbirths delivered after the 28 th week of gestation. Those diagnosed with congenital anomaly were admitted into the SCBU for observation and documentation and those that had a stillbirth were also noted. Diagnosis of NTDs was based on clinical evaluation, radiographic examination, and echocardiography of the newborn whenever recommended. Data collected included the sociodemographics of the parents, gestational age, sex of the babies; ethnicity, birth order, and consanguinity were documented. The data were recorded in a predesigned proforma. Statistical analysis of the collected data was performed using the SPSS IBM version 20.0 (IBM Corp., Armouk, NY). The results were expressed in frequencies, means, percentages, tables, figures, and charts. The Chi-square test was used for association at P = 0.05 at 95% confidence interval. The hospital's ethical and research committee approved the study.
| Results|| |
During the study period, there were 72 neonates with congenital anomalies of 10, 163 deliveries. NTDs were present in 22 cases, thus giving a prevalence of 2.2/1000 births or 30.6% of all congenital anomalies observed at the institution. There was preponderance of females, with a female to male ratio of 1.4:1. They were mainly open NTDs. The distribution of the NTDs is shown in [Table 1]. The most common type of NTDs was spina bifida (myelomeningocoele, meningocoele, and spina bifida occulta) 68.2% (15/22) and was followed by anencephaly 22.7% (5/22). There was one case of encephalocoele or cranium bifida. Among the cases of spina bifida, myelomeningocoele was present in 36.4% (8/22) of NTDs, meningocoele 27.3% (6/22), whereas spina bifida occulta constituted 9.1% (2/22) as shown in [Table 1]. Hydrocephalus was associated with myelomeningocoele in five cases (22.7%), and with meningocoele in 3 (13.6%) cases. Anencephaly was coexisting with multiple congenital anomalies (MCAs) in 2 (9.1%), whereas there were 3 (13.6%) cases of meningocoele with MCAs. Some of these MCAs include microcephaly, megacolon, and talipes equinovarus. There was no case of a congenital organic syndrome associated with NTDs in this study.
The ages of the mothers vary from 16 to 45 years, and the mean age was 27.3 (standard deviation 7.44) years. Most of the cases of NTDs 59.1% (13/16) were delivered by mothers within the age range of 20-35 years as shown in [Table 2], while teenage mothers (<20 years) accounted for 27.3% (6/22) cases of NTDs, especially those with anencephaly 18.2% (4/22). The relationship between the prevalence of NTDs and parity of the mothers is depicted in [Table 3]. NTDs are more common in the mothers of para 2-4, 59.1% (13/22) and the primipara 27.2% (6/22) and least with the grandmultiparas 18.1% (4/22). The relationship between the maternal parity and prevalence of NTDs is not statistically significant (χ2 = 0.153, df = 2, P < 0.05). History of parental consanguinity was observed in three cases (13.6%) of spina bifida and two cases (9.1%) of anencephaly.
The maternal social class greatly affected the prevalence of NTDs in this study. Majority of the mothers were of low socio-economic class (Housewives) 50% (16/22), while 2 cases 9.1% of spina bifida was observed in the neonates of 2 female medical officers as shown in [Table 4]. Diagnoses of NTDs were made both by antenatal ultrasonography 50% (11/22) and clinically (50%) after delivery as depicted in [Table 5]. Majority of the babies 68.2% (15/22) were delivered vaginally, 27.3% (6/22) by caesarean section (CS), while one diagnosed at 22 weeks gestation had medical termination of pregnancy (4.6%) as shown in [Table 5]. This though was not statistically significant (P value <0.05) as shown in [Table 6]. Most of the babies were delivered at term 90.9% (20/22), there was one case of preterm delivery (4.6%), whereas one was delivered before the age of viability (4.6%). There was antecedent maternal febrile illness on the average of 15 episodes per woman in all the trimesters of pregnancy in 81.8% (18/22) of neonates with NTDs especially among those with spina bifida. This although was not statistically significant (P < 0.05). All the cases of anencephaly and 81.3% (13/16) of spina bifida died during the perinatal period, whereas the remaining was referred to the neurosurgical team for further management.
| Discussion|| |
The birth prevalence of NTDs in this study is a 2.2/1000 births is low compared to the 7/1000 births previously reported from the middle belt region and the 2.75/1000 births from Kano in North-Western Nigeria. , The differences could be attributed to the denominator (live-births) used in the previous studies, whereas the population sampled in this included both live and stillbirths. It is however comparable to the worldwide range of 1-5/1000 births and thus agrees with the observation that reported incidence of NTDs varies from country to country and even with regions in the same country. , In a prospective review of fetal congenital anomalies in Sokoto, North-West Nigeria, Singh et al. observed that CNS anomalies were the major form of congenital malformation, and spina bifida constituted about 44% of all CNS anomalies.  It has been shown that there is decreased maternal folate level in NTD-affected pregnancies and antenatal folic acid supplementation is routinely offered to women attending antenatal care.  The incidence of NTDs has declined significantly within 30 years and now it occurs in approximately 0.5-2 per 1000 pregnancies worldwide.  High prevalence figures are now observed especially in resource poor countries where majority of pregnancies are not planned and many women book their pregnancy late in the 2 nd trimester when folic acid supplements even when consumed will be too late as the neural tube closes by the 27 th day after fertilization. Preconception care is nonexistent and a large proportion of the population in Sokoto state live in rural areas with high levels of poverty among most women. Concerted efforts at poverty alleviation at community and state levels, improved maternal health status as enshrined in the millennium developmental goals, consumption of food fortified with folic acid and increased intake of folic acid vitamin supplements among other measures will produce a decline in NTDs.
We observed that NTDs were slightly higher in females compared to males and our finding is consistent with the literature. , but a study from Kano in North-Western Nigeria detected equal male to female ratio.  The difference could be attributed to ethnic, racial, and environmental factors that are known to affect the prevalence of NTDs.  Differential rates of spontaneous abortion for male and female fetuses may account for the differences in sex-specific prevalence rates for spina bifida and other NTDs.  Combined data from studies of spontaneously aborted fetuses with NTDs indicated that 32 (56%) of 57 abortuses were male, suggesting that the overall excess of NTD-affected females among stillbirths and live-births may partially result from a higher spontaneous abortion rate for NTD-affected males than for NTD-affected females.  Various environmental risk factors have been suggested for isolated NTD such as maternal diabetes, intake of anticonvulsant drugs, other drugs with antifolate effects (methotrexate), family history of NTDs, maternal obesity, hyperthermia (febrile illness), and lower socioeconomic class. The risk factors observed in this study were a maternal febrile illness in all the trimesters of pregnancy and low-socioeconomic class even though there was no statistical significance. The maternal febrile illness, however, may not be related to the NTDs.
Most of the NTDs observed in this study were present in mothers aged between 20 and 35 years 59.1% (13/22), followed by teenage mothers 27.3%. Our observation is comparable with studies from Jos, and Kano in Nigeria, and from the Northern part of India. ,, This represents the active childbearing period in Nigeria and hence the high prevalence of congenital malformations. In contrast, other studies have observed the prevalence of NTDs more with advanced maternal age (>35 years).  Mothers of parity 2-4 were mostly affected in this study, and this is in agreement with other findings, but some studies observed a higher prevalence among the grand mutiparous women. , However, another study from India showed a high prevalence of NTDs in the primigravida. 
The major congenital anomaly coexisting with NTDS is hydrocephalus, and this was identified in 36.4% of neonates with spina bifida in our study. Hydrocephalus was present in 100% of cases of spina bifida from the study in Kano, whereas in Jos, Nigeria, the major associated anomaly detected with NTDs was talipes equino varus (35.7%). , The majority of the NTDs in this study are isolated and not associated with genetic syndromes. Association with genetic syndromes increases the risk of recurrence in siblings of affected individuals by 25% while isolated NTDs follow multi-factorial inheritance pattern.  Routine ultrasound screening during pregnancy can detect 60-80% of major and 35% of minor congenital malformations.  We have noted that about 50% of the NTDs were diagnosed during the antenatal period by ultrasound scan. Early detection of congenital anomalies is recommended so that the parents could be adequately counselled on the options of termination of pregnancy. The World Health Organization states that each and every pregnant woman should start the first antenatal care within the first trimester of pregnancy.  This however may pose some challenges in resource-poor countries like Nigeria, where many women book their pregnancies late in the gestation. 
| Conclusion|| |
The prevalence of NTDs in Sokoto is within worldwide range, and most common type is spina bifida. Hydrocephalus was the main associated congenital anomaly. Improvement of maternal nutritional status, as well as preconception folate intake, will reduce the prevalence.
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Conflicts of interest
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]
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