| Major Classifications | Type of Defects | Mode of Diagnosis | Risk of Recurrences |
| Neural Tube Defect (NTD) |
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| Isolated NTD |
| ultrasonography, X-ray, CT/MRI and necropsy | 3% - 5% after 1 affected child |
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| Anencephaly |
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| Spina Bifida (meningocele or meningomyelocele) |
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| Encephalocele |
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| Craniorachischisis |
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| Iniencephaly |
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| Anen-iniencephaly |
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| Syndromic NTD |
| ultrasonography, X-ray, CT/MRI, chromosomal analysis or molecular analysis (Meckel syndrome) and necropsy |
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| With chromosomal abnormality (trisomy 13, trisomy 18, monosomy X, etc.) | chromosomal analysis (cytogenetics, fluorescent in situ hybridization, etc.) | less than 1% plus maternal age wise risk |
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| With multiple malformation: | ultrasonography, X-ray, CT/MRI, and necropsy | sporadic to 25% |
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| Amniotic band syndrome/limb body wall complex | as above | sporadic |
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| Sirenomelia | as above | sporadic |
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| Meckel syndrome | molecular analysis | 25% |
| Chromosomal Abnormality |
| ultrasonography, X-ray, chromosomal analysis & necropsy |
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| Trisomy 18 | chromosomal analysis | less than 1% plus maternal age wise risk |
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| Trisomy 21 | chromosomal analysis | less than 1% plus maternal age wise risk |
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| Monosomy X | chromosomal analysis | less than 1% |
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| Triploidy | chromosomal analysis | sporadic |
| Amniotic band syndrome/limb body wall complex |
| ultrasonography, X-ray, CT/MRI and necropsy | sporadic |
| Hydrops fetalis |
| ultrasonography, X-ray, chromosomal analysis, inborn error of metabolism screening, necropsy and histopathology |
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| Cystadenomatoid malformation of lung |
| sporadic |
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| Twin twin transfusion syndrome |
| sporadic |
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| Umbilical cord knot |
| sporadic |
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| Idiopathic |
| sporadic to 25% |
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| Hydrolethalus syndrome |
| autosomal recessive |
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| Skeletal dysplasia |
| variable |
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| Iniencephaly |
| 3% - 5% after 1 affected child |