Which maternal health condition can lead to fetal microcephaly if uncontrolled?

Phenylketonuria (PKU) is a metabolic disorder that, if not properly managed during pregnancy, can have significant adverse effects on fetal development, including the risk of microcephaly. PKU results from a deficiency in the enzyme phenylalanine hydroxylase, leading to elevated levels of phenylalanine in the maternal bloodstream. When a pregnant woman with PKU has high levels of phenylalanine, this can cross the placenta and affect the developing fetus, leading to neurological problems such as microcephaly.

Maternal PKU is particularly critical to manage due to the potential for lifelong consequences on the child's cognitive and physical development. A strict low-phenylalanine diet is essential before and during pregnancy to minimize these risks.

While the other conditions listed may impact pregnancy and fetal outcomes, they do not typically lead to microcephaly in the same direct manner as uncontrolled PKU does. For instance, gestational diabetes primarily impacts fetal growth and may lead to macrosomia or metabolic issues rather than microcephaly, and both hypothyroidism and other maternal health conditions like Hopkins syndrome do not have the same established link to microcephaly as uncontrolled PKU.