**Core Concept**
Dengue fever during pregnancy can have severe consequences for the fetus due to the transmission of the virus from the mother. The effects can be attributed to the immune response and the release of pro-inflammatory cytokines, which can lead to fetal complications.

**Why the Correct Answer is Right**
The correct answer is related to the fact that dengue virus can cause fetal growth restriction, preterm labor, and low birth weight. This is because the maternal immune response to the virus triggers the release of cytokines, which can lead to vasoconstriction and reduced placental blood flow. This, in turn, can impair fetal growth and development.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while dengue fever can cause maternal morbidity, it is not directly associated with congenital malformations in the fetus.
**Option B:** This option is incorrect because dengue fever does not directly cause chromosomal abnormalities in the fetus.
**Option C:** This option is incorrect because while dengue fever can cause maternal mortality, it is not directly associated with fetal demise.

**Clinical Pearl / High-Yield Fact**
It is essential for obstetricians to be aware of the risk of dengue fever during pregnancy and to take necessary precautions to prevent maternal-fetal transmission. This includes screening for dengue virus in pregnant women and providing antenatal care to prevent complications.

**Correct Answer:** C. Fetal growth restriction