The most severe neural tube defect (NTD) between rachischisis and anencephaly

Between rachischisis and anencephaly, anencephaly is generally considered the most severe neural tube defect (NTD).

Anencephaly is a condition where the neural tube fails to close at the base of the skull during fetal development. As a result, the baby is born without a major portion of the brain, skull, and scalp. Babies with anencephaly usually lack the forebrain and the top of the skull. This condition is fatal, and affected babies are typically stillborn or die shortly after birth. Anencephaly represents a profound failure of brain development, resulting in a lack of essential brain structures necessary for life.

On the other hand, rachischisis is a type of NTD characterized by the incomplete closure of the neural tube along the length of the spine, resulting in an open defect in the spinal cord and vertebrae. While rachischisis is also a serious condition and can lead to significant neurological deficits, it may not always be immediately fatal, and outcomes can vary depending on the extent and location of the defect.

In summary, while both rachischisis and anencephaly are severe NTDs, anencephaly is generally considered the most severe due to the absence of essential brain structures, leading to a lack of viability.