Which of the following conditions does not typically lead to microcephaly in a fetus?

Microcephaly is a condition characterized by a smaller than average head size often associated with developmental delays. It is critical to understand the underlying causes of microcephaly in various congenital conditions to identify factors associated with fetal health.

Congenital rubella syndrome, congenital herpes simplex virus (HSV) infection, and congenital cytomegalovirus (CMV) infection are all well-documented causes of microcephaly. These infections can affect fetal brain development during critical periods of gestation, leading to abnormal neurological outcomes, including microcephaly.

In contrast, alpha-thalassemia major, a genetic blood disorder caused by a defect in hemoglobin production, does not directly cause microcephaly. While it can result in other complications such as anemia and hydrops fetalis, it does not have the same direct association with abnormal brain development as the viral infections mentioned. Therefore, alpha-thalassemia major is correctly identified as the condition that does not typically lead to microcephaly in a fetus, differentiating it from the other conditions listed that are associated with this specific outcome.