What is the most likely condition affecting the fetus of a 36-year-old woman with elevated alpha-fetoprotein levels?

Elevated alpha-fetoprotein (AFP) levels during pregnancy can indicate several potential conditions affecting the fetus, and among these, anencephaly is notably associated with high AFP levels. Anencephaly is a severe neural tube defect where the major portions of the brain, skull, and scalp do not develop, resulting in a lack of a major part of the brain. This condition typically leads to a significantly elevated AFP because the fetal tissue is not properly enclosed, allowing more of the protein to enter the maternal circulation.

Anencephaly can be detected through prenatal screening, including ultrasound and AFP testing. Elevated AFP in the context of a 36-year-old woman, who statistically has a higher risk for certain genetic disorders, crucially indicates the need for further diagnostic investigation to assess for neural tube defects, with anencephaly being one of the higher risks linked to increased AFP levels.

Other conditions listed, such as Fragile X syndrome, cystic fibrosis, and trisomy 21, do not usually present with elevated AFP levels in the same way that anencephaly does. Fragile X and cystic fibrosis are genetic conditions that are typically screened for through other methods such as carrier screening, while trisomy 21 generally presents with