What neural tube defects are associated with increased alpha-fetoprotein levels in maternal serum?

Increased levels of alpha-fetoprotein (AFP) in maternal serum are commonly associated with neural tube defects due to the disruption of the protective barriers in the developing fetus. In the case of anencephaly and spina bifida, both conditions lead to an increased risk of AFP spilling into the maternal circulation.

Anencephaly, which involves the absence of a major portion of the brain, skull, and scalp, results in the lack of a protective covering, allowing AFP to enter the maternal bloodstream. Spina bifida, a defect involving incomplete closure of the spinal column, has a similar effect, particularly in its more severe forms where the protective membranes and skin are compromised. Thus, anencephaly and spina bifida both reflect structural defects that can lead to elevated AFP levels in maternal serum.

The other conditions mentioned in the alternative choices do not typically result in elevated maternal serum AFP. For instance, while meningomyelocele is classified under spina bifida and would lead to increased AFP, conditions like hydrocephalus alone do not contribute to elevated levels of AFP as they are not defects of the neural tube closure. Therefore, the pairing of anencephaly and spina bifida is the correct association with elevated