**Core Concept**
Congenital heart disease (CHD) refers to structural or functional anomalies of the heart present at birth. Maternal health factors during pregnancy can contribute to the risk of CHD in newborns. This question requires identifying conditions that increase the likelihood of CHD in the offspring.

**Why the Correct Answer is Right**
Maternal infection during pregnancy, such as rubella, is a well-established risk factor for congenital heart disease. Maternal diabetes mellitus is also linked to an increased risk of CHD in newborns, likely due to the teratogenic effects of hyperglycemia on fetal development. Additionally, maternal phenylketonuria (PKU) can increase the risk of CHD, possibly due to the accumulation of phenylalanine in the fetus.

**Why Each Wrong Option is Incorrect**
**Option A:** The association between maternal hyperthyroidism and congenital heart disease is not well established. While maternal hyperthyroidism can affect fetal development, it is not a recognized risk factor for CHD.
**Option B:** Maternal phenylketonuria (PKU) is indeed a risk factor for congenital heart disease, as mentioned earlier.
**Option C:** Maternal diabetes mellitus is a recognized risk factor for congenital heart disease, as discussed earlier.
**Option D:** Maternal phenylketonuria (PKU) is indeed a risk factor for congenital heart disease, as mentioned earlier.

**Clinical Pearl / High-Yield Fact**
When evaluating a newborn with suspected congenital heart disease, it is essential to consider the maternal medical history, particularly conditions like diabetes mellitus and phenylketonuria, which can increase the risk of CHD.

**Correct Answer:** A.